Download Young vegetarians and omnivores

Young vegetarians and omnivores
Dietary habits and other health-related aspects
Christel Larsson
2001
Department of Food and Nutrition,
Umeå University, Sweden
Doctoral thesis
ISBN 91-7191-983-X
Copyright © by Christel Larsson
Department of Food and Nutrition
Umeå University
SE-901 87 Umeå
Sweden
Printed in Sweden 2001 by
Larsson & Co:s Tryckeri AB, Umeå
Dedicated to the Department of Food and Nutrition.
“The first…
… but not the last!”
ABSTRACT
In the middle of the 1990s many
adolescents became vegetarians. There
was concern among adults about whether
these new young vegetarians got enough
energy and nutrients from their dietary
intake. The aim of this thesis was to
investigate the prevalence of young
vegetarians, the food and lifestyle habits,
dietary intake and nutritional status of
vegetarian and omnivorous adolescents.
consumption frequency of fruits/berries,
alcoholic beverages, sweets/chocolates
and fast foods was seen between
vegetarians and omnivores. However,
female vegetarians more often than female
omnivores consumed dietary supplements.
Furthermore, lifestyle characteristics of
vegetarians were similar those of
omnivores regarding exercise, use of
alcohol and smoking habits.
The prevalence of adolescents eating a
vegetarian school lunch in 124 Swedish
secondary schools was investigated by
interviewing matrons. Information about
prevalence of vegetarians, food and
lifestyle habits, of 2041 15-year old
students from Umeå, Stockholm and
Bergen, was obtained by a questionnaire.
The dietary intake and nutritional status of
thirty 16-20 year-old vegans were
compared with thirty age, sex and height
matched omnivores.
No significant difference in validity of
reported energy expenditure or energy and
protein intakes was found between vegans
and omnivores. Young vegans (16-20
year-olds) were seen to have a higher
calculated intake of vegetables, legumes,
and dietary supplements and a lower
intake of ice creams, cakes/cookies, and
candies/chocolate than omnivores. The
dietary intake was below the average
requirements of riboflavin for 73% of the
vegans, vitamin B12 for all vegans, vitamin
D for 43% of the vegans, calcium for 77%
of the vegans and selenium for all vegans
and 43% of the omnivores. If intake of
supplements was included the intake of
e.g. calcium and selenium was still lower
than the average requirements for 67%
and 73% of the vegans respectively. Low
iron stores were as prevalent among
vegans as among omnivores (20% and
23% with low stores) and three vegans had
low vitamin B12 concentrations in blood.
Five percent of the adolescents (16-20
years) in Sweden were found to eat
vegetarian food at school lunch. In Umeå
there was a significantly higher prevalence
(15.6%) of 15-year-old vegetarians
compared with Stockholm (4.8%) and
Bergen (3.8%). It was also found that
more females than males (15 years old)
chose a vegetarian dietary regime. Even
though the female vegetarians consumed
vegetables significantly more often than
the
omnivores,
the
intake
(32
times/month) was not as often as might be
expected of a vegetarian population. The
male
vegetarians
reported
eating
vegetables not even once a day (25
times/month). No difference in the
The findings imply that food and lifestyle
habits of young vegetarians are different
than what previous studies of vegetarians
have shown. There is a need for future
research of the long-term health effects of
being vegetarian.
Key words: Adolescent, Biological markers, Dietary intake, Diet history, Doubly labeled water, Energy
expenditure, Food habits, Lifestyle, Nutritional status, Questionnaire, Vegan, Vegetarian.
CONTENTS
LIST OF PUBLICATIONS ............................................................................ 9
ABBREVIATIONS........................................................................................ 10
BACKGROUND ............................................................................................ 11
INTRODUCTION ............................................................................................. 11
DIETARY HABITS OF ADOLESCENTS .............................................................. 11
DEFINITIONS OF VEGETARIANISM ................................................................. 12
PREVALENCE OF VEGETARIANS .................................................................... 13
REASONS FOR VEGETARIANISM..................................................................... 14
HEALTH ASPECTS OF VEGETARIANISM .......................................................... 15
DIETARY ASPECTS OF VEGETARIANISM ......................................................... 16
Nutritional recommendations .................................................................. 16
Energy ...................................................................................................... 18
Protein ...................................................................................................... 18
Vitamins ................................................................................................... 19
Minerals ................................................................................................... 20
DIETARY ASSESSMENT METHODS.................................................................. 22
VALIDITY OF REPORTED ENERGY AND NUTRIENT INTAKE............................. 24
BIOCHEMICAL MARKERS OF IRON STATUS .................................................... 26
AIMS OF THE THESIS................................................................................ 28
SUBJECTS AND METHODS...................................................................... 29
SUBJECTS ...................................................................................................... 29
Definitions................................................................................................ 29
Study samples .......................................................................................... 29
Ethics........................................................................................................ 31
METHODS ...................................................................................................... 31
School Lunch Study................................................................................. 31
Adolescent Questionnaire Study.............................................................. 31
Nutritional Assessment Study.................................................................. 32
Diet history........................................................................................... 32
Validation of protein, sodium and potassium intakes ......................... 34
Validation of energy intake and expenditure ...................................... 34
Physical activity assessment ................................................................ 34
Nutritional assessments in blood......................................................... 35
STATISTICAL METHODS ................................................................................. 36
RESULTS AND DISCUSSION.................................................................... 38
SUBJECTS ...................................................................................................... 38
PREVALENCE OF VEGETARIANS .................................................................... 39
FOOD HABITS ................................................................................................ 43
LIFESTYLE RELATED CHARACTERISTICS ....................................................... 47
VALIDITY OF DIETARY INTAKE AND ENERGY EXPENDITURE ......................... 51
DIETARY INTAKE........................................................................................... 55
BIOCHEMICAL MARKERS OF NUTRITIONAL STATUS ...................................... 63
Iron ........................................................................................................... 63
Vitamin B12 .............................................................................................. 65
Vitamin D................................................................................................. 65
GENERAL DISCUSSION ................................................................................... 66
CONCLUSIONS ............................................................................................ 68
ACKNOWLEDGEMENTS .......................................................................... 70
REFERENCES............................................................................................... 72
PAPER I-V
LIST OF PUBLICATIONS
This thesis is based on the following papers, which will be
referred to by their Roman numerals:
I
Larsson C, Johansson G. Prevalence of vegetarians in Swedish
secondary schools. Scand J Nutr 1997;41;117-20.
II
Larsson C, Klock K, Nordrehaug Åstrøm A, Haugejorden O,
Johansson G. Food habits of young Swedish and Norwegian
vegetarians and omnivores Public Health Nutrition
2001;4(5):1005-14.
III
Larsson C, Klock K, Nordrehaug Åstrøm A, Haugejorden O,
Johansson G. Lifestyle related characteristics of adolescent lowmeat-consumers and omnivores in Sweden and Norway
(Accepted for publication in J Adolesc Health 2001).
IV
Larsson C, Westerterp K, Johansson G. Validity of reported
energy expenditure and energy and protein intakes of Swedish
vegan and omnivore adolescents (Accepted for publication in Am
J Clin Nutr 2001).
V
Larsson C, Johansson G. The dietary intake and nutritional status
of young vegans and omnivores in Sweden (Accepted for
publication in Am J Clin Nutr 2001).
9
ABBREVIATIONS
BMI
Body mass index
BMR
Basal metabolic rate
BSE
Bovine spongiform encephalopathy
DLW
Doubly labeled water
EEmea
Measured energy expenditure
EIrep
Reported energy intake
FIL
Food intake level
NNR
Nordic nutrition recommendation
PABA
Para-aminobenzoic acid
PAL
Physical activity level
SD
Standard deviation
TIBC
Total iron binding capacity
10
Background
BACKGROUND
Introduction
This thesis focuses on some of the
nutritional and health impacts of
the dietary regimen and lifestyle of
young vegetarians compared with
young omnivores. In the middle of
the 1990s mass media focused on
animal liberation actions, animal
transportation, cruelty to animals
and young people becoming
vegetarians. There was concern
among parents, school staff and
nutritionally-aware people, that
these new young vegetarians did
not get enough energy and
nutrients from their dietary intake.
A
public
discussion
about
disadvantages and advantages of
becoming a vegetarian at a young
age took place and many
statements
were
based
on
speculation rather than scientific
knowledge. To obtain more
knowledge about the new and
presumably
increasing
phenomenon
of
adolescents
becoming vegetarians, a study of
young omnivores and vegetarians
was
implemented
at
the
Department of Food and Nutrition,
Umeå University.
nutrients and irregular meal
pattern1, 2, 3, 4, 5. Studies have shown
that adolescents have a low and
infrequent
consumption
of
vegetables and fruits 2, 6, while milk
and bread as well as sweets are
consumed daily2, 7. In general, food
intake is quite similar between
male and female adolescents, but
males eat larger amounts of
food2, 3. However, the small
differences seen point to healthier
food intake among females as they
eat vegetables more often and
consume fewer sweets2.
A
high-energy
intake
in
combination with low energy
expenditure leading to overweight
seems to become more prevalent
among adolescents in Sweden1. In
general, adolescents’ dietary intake
of vitamins and minerals are, with
some exceptions, adequate for
normal health and growth1. Dietary
calcium intake has been shown to
be high, while the intake of fiber,
vitamin D, zinc and selenium and,
in females iron, is below the daily
recommendations of the Nordic
nutrition
recommendations
1, 3
(NNR) .
Dietary habits of
adolescents
Snacking and light meals are very
common among adolescents and
contribute with 25-35% of the
daily energy intake1. Questionnaire
studies of Swedish 14-15 year-olds
Dietary
habits
of
Swedish
adolescents
are
in
general
characterized by omnivorous food
intake, adequate intake of most
11
Background
dietary intake, and the most
common types of vegetarians are
shown in Table 18, 9, 10.
found that many adolescents skip
breakfast and the free school lunch,
while most eat dinner in the
evening1, 2, 4. Adolescents who ate
no breakfast (8-11%) were found
to skip the school lunch more often
than those who ate breakfast4, 5. It
was also shown that more males
than females ate school lunch,
otherwise differences of meal
patterns with respect to gender
were small3, 4, 5. Poor meal habits
of adolescents were also found to
be
associated
with
other
undesirable lifestyle factors, such
as smoking and use of alcohol2, 4.
Semi-vegetarians
are
also
sometimes
called
demivegetarians, pesco-vegetarian and
near-vegetarians, and some studies
also include people in this
subgroup who eat poultry or with
rare and infrequent meat intake8, 9.
Defining a person as a vegetarian,
even though the person actually
eats some animal products such as
fish, poultry or pork, may be
controversial, since they are not
vegetarians in the strict sense of the
word, rather non-red-meat eaters.
Other types of vegetarians are
fruitarians who are people who
only eat those parts of the plant that
are cast off or dropped from the
plant and that does not involve any
destruction of the plant itself8, 9. A
macrobiotic diet may be a
vegetarian diet, depending on how
it is followed8, 9. The followers of
Zen macrobiotic diet advance
through ten stages of progressive
dietary
restriction
aiming
ultimately at a diet composed of
cereals only11.
Some adolescents choose to eat
vegetarian food but few studies
have investigated the food intake
of vegetarian, especially vegan,
adolescents.
Definitions of vegetarianism
Vegetarianism is the dietary
practice of people abstaining from
some or all animal products8, 9. The
term vegetarian is often used to
include people who eat all types of
vegetarian diets which, in reality
can be highly variable. Today
vegetarians are divided into several
different subgroups based on their
Table 1 Foods eaten by different types of vegetarians. The plus (+) sign indicates that the diet
comprises the foods. The minus sign (-) indicates that the diet does not comprise the foods.
Type of vegetarians
Foods eaten
Plant foods
Dairy products Eggs
Fish
Meat
Vegans
+
Lacto-vegetarians
+
+
Lacto-ovo-vegetarians
+
+
+
Semi-vegetarians
+
+
+
+
-
12
Background
were vegetarians in 199016. This
prevalence is an increase of 23%
since the previous Gallup for the
Realeat Company Ltd survey in
1988 and a 76% increase since the
first survey in 1984.
A person may consider him or
herself a vegetarian even though
the diet has a frequent content of
animal products when eating out,
although a more appropriate name
would be lacto-ovo-fish-steak only
when I eat out-vegetarian12. It has
been proposed that the criterion for
defining a vegetarian diet should
more emphasize the presence of
vegetables, fruits, grains and other
plant foods rather than the absence
of animal products13. Further, it has
been suggested that people who do
not have a daily consumption of
fruits, vegetables and whole-grain
cereals should not be considered
vegetarians, regardless of their
consumption of animal products13.
In Sweden, as well as in many
other countries, few investigations
of the prevalence of young
vegetarians
have
been
published10, 17. Table 2 shows the
results
from
six
different
prevalence studies of young
vegetarians during 1994-2001.
The increase in vegetarianism has
been stimulated by media focus on
cruelty to animals and more
recently
bovine
spongiform
encephalopathy (BSE) also called
mad cow disease. It has been
reported that women between 1518 years old have the highest
tendency to be vegetarian4, 10, 18,
and that more adolescent females
from high rather than low socioeconomic status areas, have
thought
about
becoming
vegetarian10.
Prevalence of vegetarians
Currently, there is an increasing
trend towards vegetarianism in the
Western world10. The prevalence
of vegetarians among 170 000
British adults was 4.5% in
199514, 15. A British Gallup for the
Realeat Company Ltd, based on a
sample of 4 162 respondents aged
16 years and over (stratified by
region and town) showed that 3.7%
13
Background
Table 2 Prevalence of young vegetarians according to different studies during 1994-2001. The
prevalence of all vegetarians has been reported by all studies but not always the prevalence of
different types of vegetarians.
Country
Study design
Yeara Age
nb
Sex
SVc LVd Ve Allf
(years)
(%) (%) (%) (%)
Australia
Questionnaire, 1994
16
536 female 16
21
(south)10
self reported
416 male
6.0
7.0
vegetarianism.
England18
Weighed diet
1999 15-18
264 female
10
record.
258 male
1.0
Finland,
Questionnaire,
(Helsinki)19, g completed by
school staff.
Sweden4
Questionnaire,
self reported
vegetarianism.
Swedeng, h
Telephone
interview with
school staff.
USAi
Not presented.
a
b
c
d
e
f
g
h
i
1999
14-16
16-20
8 764
6 731
mixed
mixed
-
-
-
4.0
17
1996
15-16
15-16
2 956
3 071
female
male
2.0
1.0
2.0
1.0
<1.0
1.0
5.0
3.0
2001
16-20 76 512 mixed
-
-
0.6
11
2000
17-24
-
-
-
11
4.0
1 141
female
male
Year when the study was conducted.
Number of people studied.
SV = Semi-vegetarians.
LV = Lacto-vegetarians.
V = Vegans.
All types of vegetarians, including: SV, LV, V.
Investigated the prevalence of people eating vegetarian food at school lunch.
Follow-up study with 104 secondary schools of the same sample as in paper I, plus 19
nearby schools 20.
JMA Student Omnibus, January 2000. Survey of students in full time higher education.
Reasons for vegetarianism
There is most often no single
motive for becoming or being a
vegetarian. Among the reasons
given for being so, are often the
following16;
Ethical reasons – ethical issues
revolving around treatment of
animals23.
Environmental
reasons
ecological concern about
environment8, 23.
Health reasons – to obtain and
maintain better health or decrease
symptoms
or
risk
of
21, 22, 23
diseases
.
the
Philosophical
and
religious
reasons – Seventh-day Adventists,
14
Background
health31, 32. Health studies of
groups of vegetarians such as
Seventh-day
Adventists
and
Trappist
monks
show
that
vegetarianism may not only sustain
health, but also improve health33, 34,
35, 36, 37, 38
. These effects may be
attributable to diet as well as to
other lifestyle characteristics, such
as maintaining desirable body
weight, regular physical activity
and refraining from alcohol,
tobacco and drugs23.
Hindus, Buddhists, some so called
New Age groups, groups of Hare
Krishna and Trappist monks
emphasize vegetarianism8, 11, 14, 23.
Economical reasons – when meat
is more expensive than vegetables8,
23
. However, it is rare in Western
countries to become vegetarians for
economical reasons24.
Reasons for eating a vegetarian diet
are
highly
individual
and
changeable. Health may be the
initial motive but ethical issues
may become the most important
factor for continuing to eat a
vegetarian diet or vice versa16.
Today, young vegetarians make
their choices mainly for ethical
reasons, including concern about
animal husbandry and animal
welfare10, 16, 25, 26. Other reasons
why adolescents avoid animal
products include fashion, curiosity,
rebelliousness,
convenience27,
liking animals26 and body weight
concern28. There may also be the
perception that meat is harmful26, 29
and a reaction to food safety
‘scares’ such as the mad cow
disease (BSE), Creutzfeldts Jacob’s
disease, salmonella, and the use of
antibiotics29 and hormones in meat
production30.
Health aspects of
vegetarianism
There is a scientific consensus that
a higher intake of plant foods and
less animal foods promotes
15
Western vegetarians have shown to
be leaner than omnivores and have
a lower risk of obesity 39, 40, 41. The
reduced risk shown among
vegetarians
of
non-insulindependent diabetes may partly be
explained by vegetarians being
leaner than omnivores23, 24, 39.
Blood
pressure,
hypertensive
disorders and other risk factors for
coronary heart disease are also
reported to be lower among
vegetarians, especially vegans, than
among the general population42,
43, 44
. Furthermore, it has been
shown that a vegetarian regimen
reduces mortality from ischaemic
heart disease by about 25% 41, 45, 46.
Even though it has been concluded
that there are no differences in
mortality from common cancers
(stomach, colorectal, lung, breast
and prostate)41, 47, 48 between
vegetarians and omnivores, there
are studies demonstrating an
inverse
association
between
vegetable and fruit intake and
many cancers 49, 50.
Background
Dietary aspects of
vegetarianism
believe that their diets are
somehow guaranteed to be healthy
and
nutritionally
adequate14.
Nutrition often comes low on the
priority list of adolescents, and
poor eating habits sometimes
typify this group no matter if they
are vegetarians or omnivores.
However, previous studies have
suggested
that
adolescents
following a vegan diet are at
greater risk from nutritional
inadequacy than those following a
lacto-ovo-vegetarian diet or an
The
omnivorous
diet27, 56.
consequence of a more restrictive
diet is an increased difficulty in
achieving nutritional adequacy,
which means that greater care must
be taken.
Adolescents who consume a wellplanned vegetarian diet can
generally meet all their nutritional
requirements for growth15, 23.
However, those who follow a
vegan diet need to make sure that
they consume reliable sources of
energy, vitamin B12 and vitamin D,
if sunlight is limited51. Iron, zinc
and calcium intakes may also
deserve special attention although
intakes are usually adequate when
there is a reasonable variety of
foods
and
when
energy
requirements are met23.
Much has been written about adult
vegetarianism and nutrition but few
studies have examined adolescent
vegetarianism10, 51, 52. Nutrient
intake during adolescence is
important for growth, and longterm health promotion53, 54.
Furthermore, since adolescents are
becoming
more
autonomous,
behavioral patterns acquired during
this period are likely to influence
long-term behavior.
Nutritional recommendations
Well-planned vegetarian diets can
effectively meet the Nordic
nutrition recommendations (NNR)
and can be health-supporting.
However, there are distinctions
between the various types of
vegetarian regimens concerning
their impact on nutrient intake,
nutritional status, and overall
health8. The NNR are, with the
exception of zinc, the same for
vegetarians as for omnivores.
Meat avoidance amongst teenage
girls in the UK has, in the mid
1990s, gained in popularity, and
there have been concerns about the
nutritional adequacy of a meat-free
diet in this population group55, 56.
Some omnivores are of the opinion
that young vegetarians, especially
vegans, are generally undernourished whereas some vegans
In the NNR a daily recommended
nutrient intake (RI) is defined as
the average requirements (AR) of a
population plus a safety margin of
16
Background
is important to obtain enough
nutrients to prevent deficiency and
thereby adverse symptoms. When
evaluating nutritional intake of a
group of people, estimated by a
dietary assessment method, it is
appropriate to use the average
requirements (AR) without the
safety margin. Having a nutrient
intake lower than the AR indicates
an increased probability that too
little nutrients are being eaten57, 58.
Number of people
at least two standard deviations
(SD) 57, 58 (Figure 1). The lowest
recommended intake (LRI) of a
given nutrient is defined as the
average requirements (AR) of a
population minus 2 SD. This is the
amount below which there is an
increased probability of deficiency
symptoms. Even if a person’s daily
nutritional intake is lower than the
lowest recommended intake (LRI)
for a while, deficiency need not
follow. However, in the long run it
RI = AR + 2 SD
AR
LRI = AR – 2 SD
Requirement of nutrient intake
Figure 1 Definitions of the lowest recommended intake (LRI), average requirements (AR) and
recommended intake (RI) of a nutrient per day57.
17
Background
day60. Vegetarian diets that are not
properly planned tend to be
characterized by exclusion of
animal
products
without
replacement with nutritionally
equivalent plant foods. Examples
of this are when a person becomes
vegan and excludes milk, and
water becomes the beverage of
choice or when milk based
margarines/butter are excluded,
and
no
spread
is
used.
Furthermore, lettuce and cucumber
sometimes continue to be the major
vegetables instead of, for example,
peas, carrots and broccoli.
However, in cases where the
vegetarian diet has been properly
planned it has been concluded that
energy intakes are adequate8, 15, 61.
It has been suggested that
vegetarians
have
a
better
understanding
of
dietary
requirements than the general
population59. Many vegetarians,
especially vegans, are well
informed on general nutrition but
would
like
more
detailed
knowledge, either for their own
interest or to answer the questions
about their diets that vegans are
inevitably asked14.
Energy
A person’s energy requirements
depend on many factors, such as
age, sex, body weight and physical
activity14. Apart from basal
metabolic rate (BMR), physical
activity has the greatest impact on
energy expenditure, and a correct
energy requirement cannot be
estimated without taking this into
consideration.
Vegetarian diets are most often
composed of less total fat and
protein, but more total complex
carbohydrates than omnivorous
diets, and consequently vegetarians
are likely to consume less total
food energy (calories)46. The high
carbohydrate content of some
vegan diets may also lead to a
significant bulk effect with an
increased risk of not meeting the
energy
requirement8.
Special
attention must be given to meet the
energy needs of vegetarian
adolescents who consume a lot of
low-fat products, and those who
limit the number of meals eaten per
18
Protein
The traditional concern about
vegetarians’ diets has been the
adequacy of protein intake,
especially of the essential amino
acids46. Some authorities suggest a
10% higher protein intake when
plant food is the main protein
source, since protein from plant
sources may be slightly less
digestible14. The digestibility of
proteins may be affected by the
structure of the protein itself, as
well as by other factors such as the
amount of dietary fiber, tannins
and phytates in the food14. The
quality of vegetable protein in the
diet may be improved by
combining food products with
different amino acid profiles. For
example, cereal grains that are low
Background
in the essential amino acid lysine
but adequate in methionine, can be
complemented by legumes having
adequate
lysine
but
little
methionine. However, it is usually
not a problem for vegetarians to
obtain an adequate protein intake
and it is not necessary, as
sometimes
believed,
to
complement amino acids at each
meal14, 61. Good plant protein
sources for vegetarians are a
mixture of grains, legumes, nuts,
seeds and soya foods8, 14, 62. Most
individuals complement proteins
unconsciously e.g. bean-based
soups with a slice of bread,
combining beans and rice or eating
a bean burrito.
Vitamins
The vitamin intake of vegetarians
has been studied by analyzing both
food intake and plasma levels and
most often vegetarians have an
adequate intake of vitamins63, 64, 65.
Vitamin B12 is the most likely
nutrient to be found lacking in a
strict plant-based diet61, since it can
only be derived from animal and
bacterial sources. Plant foods do
not contain the vitamin unless they
are contaminated with B12–
producing bacteria14. For many
years it was thought that fermented
soya foods such as soya sauce,
tempeh and miso contained some
genuine vitamin B12, owing to the
presence of certain microorganisms
8, 14
. It was also believed that edible
seaweeds e.g. Nori and a blue-
19
green algae called spirulina, which
often are contaminated by
plankton,
contained
genuine
vitamin B12. However, vitamin B12
analogues (80-94% found in these
food products) do not have any
bioactivity in the human body, and
there is a possibility that their
presence may actually block the
body’s ability to use genuine
vitamin B1214, 23. A better and more
reliable dietary source of vitamin
B12 for vegans is nutritional
yeast8, 14. The yeast produces no
genuine
vitamin
B12
itself
(although
several
inactive
analogues), but contains active B12
derived from the B12–enriched
molasses medium on which it is
grown14. Other reliable sources of
B12 are fortified products, such as
yeast extracts, oat beverages, some
soya beverages, margarines and
lately mineral water in Sweden.
Intestinal bacteria in humans
produce active B12, but mostly in
the colon where it cannot be
absorbed, rather than in the small
intestine where it would have had a
chance of being absorbed14.
Furthermore, to be absorbed
effectively from food, vitamin B12
has to be linked to a so-called
intrinsic factor. The most common
cause of vitamin B12 deficiency in
the general and older population is
lack of this intrinsic factor, rather
than an inadequate dietary
intake14, 23. Vitamin B12 is stored in
the liver, which normally contains
sufficient amounts (2-5 mg) for a
period of three to six years, even in
Background
the total absence of a food source14.
For this reason, although official
recommendations are expressed as
a daily amount, it is not actually
necessary to consume the vitamin
every day. However, a long lasting
vegan
diet
ought
to
be
complemented with either vitamin
B12 supplement or vitamin B12
fortified foods to ensure adequate
intake8, 14.
Plant foods, except plankton66 and
some mushrooms67, 68, 69 e.g.
chantarellus tubaeformis and
shiitake, do not contain vitamin D,
but some soya drinks, margarines
and breakfast cereals acceptable for
vegans are fortified with vitamin
D2 (ergocalciferol, obtained from
yeast and other fungi)14. Vitamin
supplements,
which
contain
vitamin D2, are also suitable for
vegans. However, food sources of
vitamin D may be of minor
significance, since vitamin D is
produced from the action of ultraviolet B light on sterols in the skin.
A cloudy summer day will be
enough to stimulate formation of
vitamin D in the skin and most
people need little or no extra
vitamin D from food14. However,
the effective light wavelength is
probably not present in winter
sunlight between October and
March in northern Sweden. Thus
winter time supplies of vitamin D
depend on dietary sources or on the
previous
summer’s
exposure
creating adequate stores in the
liver. Even though the vitamin D
needs may be achieved by
exposure to ultra-violet light,
people (especially children) living
in
northern
countries
are
recommended to obtain vitamin D
from the diet or supplements
during winter time to prevent
deficiency58.
20
Minerals
Several studies have found mineral
intake to be adequate in
vegetarians, with the possible
exceptions of iron and zinc46.
Nonheme-iron is the type of iron
found in a strict vegetarian diet
while an omnivorous diet contain
both nonheme-iron and heme-iron.
Only 1-8% of the nonheme-iron in
plant foods, while up to 22% of the
heme-iron in meat is absorbed14. A
low intake of iron in the diet is
partly compensated for by
increased absorption rate, but in
chronic dietary deficiency the body
stores run down resulting in iron
deficiency. Approximately 20% of
the world population have iron
deficiency70, 71 and low iron status
is also relatively widespread in
Sweden, especially among female
adolescents. Symptoms of iron
deficiency anemia include e.g.
tiredness, headache and poor
concentration. A study of 179
vegetarians showed that 19% were
classified
as
having
iron
deficiency72. Another study of 50
vegetarian women (18-45 years)
and 24 age-matched omnivores
showed that a similar proportion
(18%)
of
vegetarians
and
Background
other organic acids such as malic
acid in e.g. plums and apples and
citric acid in citrus fruits8, 14. Zinc
absorption may be promoted by
protein from fish and eggs if those
foods are included in the vegetarian
diet, or by fermented food76.
omnivores (13%) had serum
ferritin concentrations <12µg/L
and no significant difference in
hemoglobin concentrations73.
Zinc is important for protein
metabolism, cell growth and repair,
and immune function74. Because of
low bioavailability the NNR gives
a 25-30% higher recommendation
of zinc for vegans58. Good plant
sources include grains, nuts and
legumes23. A suboptimal serum
zinc level has been shown among
24% of 79 lacto-ovo-vegetarians
and 18% of 29 omnivores (14-19
years)75.
Vegetarian diets, especially vegan
diets, most often contain less
calcium than omnivorous diets78. It
has been suggested that vegetarians
are likely to need less calcium than
omnivores since the vegetarian diet
is moderate in protein as well as in
sodium (salt)79. High protein intake
has been shown to lower the
acidity (pH) of the urine with an
increased urinary excretion of
calcium as a consequence80. On the
other hand, a recent study showed
no association between the intake
of
protein
and
calcium
81
absorption .
Vegetarians
consuming a diet low in calcium
have a more efficient absorption of
calcium compared with people
with adequate intake78. It is not
known, however, if this improved
absorption compensates fully for a
low calcium intake, or to what
extent a lower protein, and sodium
intake of vegans reduce their
calcium requirements. Thus, it is
important for those who avoid
dairy products to ensure an
adequate calcium intake from the
diet, by eating enough calcium rich
plant foods, using calcium-fortified
foods
or
supplements.
Furthermore, it is important not to
Although iron and zinc are found
in a fairly large number of plant
foods, their bioavailability is
questionable due to interference of
antagonists8. Dietary strategies to
enhance
the
content
and
bioavailability of iron and zinc in
vegetarian diets include decreasing
intake of antagonists as well as
increasing intake of promoters14, 72,
76, 77
. Examples of an antagonists
are tannins from e.g. tea which
reduces
the
absorption
of
nonheme-iron, as well as phytates
found in nuts, cereals, seeds and
legumes which reduce the
absorption of both iron and zinc.
Phytate in plant foods can be
decreased by yeast fermentation of
whole-wheat flours when baking
bread. Examples of promoters,
which can increase absorption of
nonheme-iron are vitamin C and
21
Background
Food records aim to collect data at
the time of eating during one or
several days. The subject describes
every food item eaten by taking
notes, and portion sizes are either
estimated by piece and household
measures, or weighed before being
eaten. A most significant problem
is the tendency of subjects to eat
less the more the days of
continuous diet recording go on,
indicating a tendency to change
dietary habits, more likely to ones
that are healthier than usual. This is
one of the reasons why the method
might not be suitable to use in a
comparison study of the nutritional
aspects of a vegetarian and
omnivorous diet. The method may
also be difficult to use on e.g.
adolescents who eat a lot of food
outside home and lack time and
motivation to make a careful food
record. It may also be difficult to
persuade adolescents to participate
in a food record exercise since
several days of recording are
needed, up to twenty days for some
nutrients85. The necessity to repeat
the number of measured days is a
problem for food records when
good estimates of individual
nutrient intakes are to be obtained.
This is a serious impediment when
investigating adolescents.
have a too high intake of protein
and sodium79, 82.
The selenium content of foods
varies widely and in plants it is
largely dependent on the amount of
selenium in the soil78. In Sweden,
selenium intakes tend to be low as
the soil contains little selenium and
locally grown crops therefore are
poor sources83. In a Swedish study,
a vegan diet contained very low
amounts of selenium compared
with a lacto-vegetarian and an
omnivorous diet, mainly because
mostly locally grown rather than
imported products were eaten64. In
contrast, in another Swedish study,
a lacto-vegetarian diet contained
rather high values of selenium
compared with that of an
omnivorous diet. This may be
explained by the fact that the
vegetarians ate imported cereals,
legumes and nuts which seemed to
be the major sources of selenium63.
Dietary assessment methods
The most common dietary
assessment methods in nutritional
surveys are food records, 24h
recalls, diet histories and food
frequency questionnaires84. Each
method has its own advantages and
disadvantages. Which one to use
depends upon e.g. the aim of the
study, availability of time, money
and the number and properties of
the subjects.
24h recalls aim to give
information about the dietary
intake during the preceding 24
22
Background
demand and time of participation
will be less with diet histories
compared with both 24h recalls
and food records, since several
days of food record or 24h recalls
are needed to obtain a valid dietary
intake. Therefore diet histories may
be more suitable to use on e.g.
adolescents. Furthermore, the
method is retrospective and will
not change the dietary habits of the
subjects. The method may also be
suitable for vegetarians who eat
uncommon food products and
dishes since they will have the
opportunity to describe the dietary
habits in detail.
hours. The subject is interviewed
about what type and amount of
food items have been eaten and
portion sizes are estimated in piece,
household measures or with
pictures of different portion sizes.
The major advantage of 24h recalls
is that it is quick and simple for
both interviewers and subjects.
However, to obtain information
about day-to-day variation in
nutrient intake several 24h recalls
and skilled interviewers are
needed. The method is dependent
on accurate memory, food
description and estimates of
portion sizes. Unfortunately, this is
the method that yields most
underreporting86. The method may
not be suitable for e.g. young
people who have an active life and
are difficult to persuade to
participate in an interview at short
notice, especially when the
interviews have to be repeated
several times.
Diet histories, introduced by
Burke et al87, aim to give
information about habitual intake
during a period of time e.g. one
month or six months. Most often it
involves a questionnaire, an
interview and sometimes a food
record. The information collected
includes usual meal pattern,
frequency of consumption and
estimated portion size. The method
requires skilled interviewers and is
more demanding for the subjects
compared with a 24h recall.
However, in the end the total
23
Food frequency questionnaires
aim to estimate the frequency of
consumption of different food
items during a period of time e.g.
three months or one year84, 88. The
questionnaire may be selfadministered or used in an
interview and is sometimes focused
on specific groups of food and
sometimes the total food intake.
However, the total food intake is
almost impossible to cover. The
questionnaire may be semiquantitative by including questions
about portion sizes with fixed
definitions of, for instance, small,
medium, or large portions84. The
major advantages of a food
frequency method are that it could
be low in cost, quick and
representative84. The method may
be suitable for adolescents since it
is simple and quick, which
increases the possibility of
Background
assessment methods there is a need
to validate each method used. The
validation may be either relative
with another dietary method89 or
absolute with biological markers
such as doubly labeled water
(DLW) and nitrogen excretion in
24-h urine collections 90, 91, 92.
obtaining a high participation rate.
However, the most significant
problems with questionnaires are
the uncertain validity, the difficulty
in developing a relevant and
representative questionnaire and
problems of obtaining the total
food intake. This is especially a
problem
when
the
same
questionnaire is completed by
subjects with different types of
diets
e.g.
omnivores
and
vegetarians.
Validity of reported energy
and nutrient intake
The doubly labeled water (DLW)
method, is used, for instance, to
make an accurate assessment of
energy expenditure of a free-living
person93, 94, 95 and to validate
reported energy intake. The
principle of the DLW method is
that deuterium equilibrates with
body water, and oxygen-18 with
both water and the bicarbonate
pool of the body96. The measured
energy expenditure (EEmea) is used
to validate reported energy intake
(EIrep) and the EIrep/EEmea ratio
should equal 1.0 if there is a true
estimate of reported energy intake
of a person in weight stability. The
energy expenditure divided by
BMR gives a physical activity
level (PAL) and the energy intake
divided by BMR gives a food
intake level (FIL)93, 97. Both PAL
and FIL are multiples of BMR and
ought to be >1.2 to be consistent
with long-term survival57. The
DLW method can be used on
anyone and is suitable for studying
busy people in a free-living
situation, e.g. adolescents who may
be difficult to persuade to
The dietary methods described are
dependent on a food composition
database to convert foods into
nutrient content. Both the dietary
methods and the food composition
database are developed to assess an
omnivorous diet. When assessing
vegetarian diets it is important to
know about commonly used
vegetarian food products and to
include these in the interview
and/or questionnaire. Problems
often arise when vegetarian food
products are not included in the
food composition database. If
possible the recipes or information
about nutrition content in the
vegetarian products ought to be
entered in the database.
Valid information about dietary
intake may be difficult to obtain,
especially from young people,
where the adolescent has irregular
meal habits and is not involved in
the preparation of the food. Since it
is difficult to obtain valid
information
with
dietary
24
Background
participate in a study if it is too
demanding and time consuming.
urine during 24 hours and obtain a
complete collection.
Estimating the validity of reported
nitrogen (protein), sodium and
potassium intake involves one or
several 24-h urine collections i.e.
collection of the total amount of
urine excreted during 24 hours98, 99.
The amount of nitrogen, sodium
and potassium excreted in 24-h
urine is analysed and used as
biological markers for nitrogen
(protein), sodium and potassium
intake, respectively. Bingham et
al92, showed that 81% of nitrogen
intake is excreted in urine, thus
excreted nitrogen divided by a
factor 0.81 should be equal to
nitrogen intake. Sodium excretion
in urine and potassium excretion in
urine and feces are the biological
markers for sodium and potassium
intakes, respectively100, 101, 102.
Johansson et al100 showed that 77%
and 73% of the potassium intake
from an omnivorous and a lactovegetarian diet respectively, was
excreted in urine. One major
problem in validating the intakes of
protein, sodium and potassium is
the inconvenience for subjects to
collect, often several, 24h urine
samples. This may lead to the
situation where only wellmotivated volunteers take part in
validated studies and thus, that
people that are not well-motivated
will not be studied or take part in
studies with low compliance. For
instance, it may be difficult to
persuade adolescents to collect
The completeness of a 24-h urine
collection
is
estimated
by
analyzing the content of paraaminobenzoic acid (PABA) in
urine. The principle of the method
is that a subject ingests three 80 mg
tablets of PABA, one in the
morning, one at midday and one in
the evening during the day of urine
collection, and a similar amount
(240 mg) of PABA ought to be
found in the 24-h urine collection if
it is complete. Bingham et al92
showed that 93 ± 4% of the PABA
was excreted in urine and ±2 SD
from the mean excretion resulted in
the interval 85-101% of PABA
recovery. A 24-h urine collection
with a PABA recovery between
85-101% may be classified as a
complete 24-h urine collection.
Unfortunately, it has been shown
that
complete
24-h
urine
collections are very difficult to
obtain90, 103. Therefore, to make use
of incomplete 24-h collections a
linear regression compensation
method for collections with PABA
recoveries between 50-85% has
been developed103. This method is
indispensable
when
studying
people, e.g. adolescents, who find
it difficult to make complete 24-h
urine collections.
25
Background
Biochemical markers of iron
status
The four to five grams of elemental
iron present in a normal adult can
be
divided
into
three
compartments; functional iron
compartment (74%) with the
essential metabolically active iron,
in iron-requiring proteins and
enzymes e.g. hemoglobin and
myoglobin104.
Storage
iron
compartment (25%) with ferritin as
the major storage protein, and the
liver and bone marrow as the
greatest storage tissues of the
human body. The link between the
storage and functional iron
compartments is the smaller
transport iron compartment (<1%),
consisting of transferrin. The
transferrin iron is delivered to
tissues via transferrin receptors
expressed on virtually all cells of
the body.
S-ferritin is a more reliable
quantitative laboratory measure of
iron
status
compared
with
77
hemoglobin . The main drawback
of serum ferritin is the false
elevation that occurs with chronic
inflammation or infection and
therefore the level of different
immune cells are also usually
estimated in the same blood
sample. The function of ferritin in
serum is unknown but in most
individuals the concentration of Sferritin parallels the total amount of
storage iron, and it is the only iron
status index that can reflect a
deficient, normal or excessive iron
status105. S-ferritin levels fall early
during iron deficiency, before the
characteristic
changes
in
hemoglobin, S-iron and total iron
binding capacity (TIBC).
Hemoglobin is the oxygen
carrying pigment of red blood
cells105.
Each
hemoglobin
molecule is a conjugate of a protein
(globin) and four molecules of
heme, which contains iron.
Measurement of the hemoglobin
concentration is the most widely
used screening test for iron
deficiency.
However,
the
hemoglobin concentration in serum
is a crude, non-specific index of
iron status77 and the hemoglobin
concentration falls only in the later
stage of iron deficiency (Figure
2)105.
S-iron is a measure of the number
of atoms of iron bound to the
transport protein transferrin105.
Each molecule of transferrin can be
bound to one or two atoms of iron.
Iron deficiency results in a fall in
S-iron levels.
TIBC is related to the total number
of free iron binding sites on the
transport protein transferrin105. Iron
deficiency is associated with a rise
in TIBC from the increase in the
number of free iron-binding sites.
26
Background
S-iron, TIBC and transferrin
saturation are particularly useful
for
differentiating
between
nutritional deficiencies of iron and
iron deficits arising from chronic
infections,
inflammation,
or
chronic neoplastic diseases105.
Transferrin
saturation
is
calculated by dividing the S-iron
content with TIBC and multiplying
by 100 to give a percentage
value105. Transferrin saturation is a
measure of the iron supply to the
erythoid bone marrow. Since Siron decreases and TIBC increases
in a situation of iron deficiency, the
transferrin saturation decrease.
Replete
iron stores
Depletion of
storage iron
Depletion of functional iron
Transport iron
Hemoglobin
S-ferritin
S-iron
Transferrin
saturation
TIBC
Figure 2 Changes in hemoglobin, serum ferritin, serum iron, transferrin saturation and total
iron binding capacity (TIBC) at different levels of iron status. Iron status is ranging from
replete iron stores, depletion of storage iron, and depletion of functional iron. Revised drawing
from Suominen et al, 1998106.
27
Aims of the thesis
AIMS OF THE THESIS
The general aim of the present thesis was to describe the prevalence of
vegetarians, the food habits, the dietary intake and the nutritional status of
young vegetarians and omnivores, and health-related lifestyle characteristics.
The following objectives were elaborated:
To investigate the prevalence of students (16-20 year olds) choosing to eat
various types of vegetarian school lunches in Swedish secondary schools
(School Lunch Study, paper I).
To compare food habits between different types of vegetarians and
omnivores among 15-year-old adolescents in Sweden and Norway, and to
determine the prevalence of vegetarians (Adolescent Questionnaire Study,
paper II).
To describe lifestyle related characteristics of 15-year-old low-meatconsumers and omnivores living in Sweden and Norway (Adolescent
Questionnaire Study, paper III).
To validate a physical activity interview and a diet history interview for
estimating energy expenditure, and energy and protein intakes in young
Swedish vegans and omnivores, 16-20 years old. The validity was
estimated by comparison with measured energy expenditure and
biological marker for nitrogen intake (Nutritional Assessment Study,
paper IV).
To assess the dietary intake and nutritional status of a group of Swedish
vegans in the 16 to 20 year old age range living in Umeå, using a
validated diet history method and blood samples. Furthermore, and to
compare the results with sex-, age- and height-matched omnivores
(Nutritional Assessment Study, paper V).
28
Subjects and methods
SUBJECTS AND METHODS
Subjects
Definitions
In this thesis adolescents were
categorized into vegans, lacto(ovo)-vegetarians (including lactovegetarians
and
lacto-ovovegetarians),
semi-vegetarians
(lacto-ovo-fish-vegetarians)
and
omnivores depending on their
dietary intake. The category ‘semivegetarians’, includes adolescents
eating sausage, poultry and pork
never or seldom during the last 12
months. The term ‘vegetarian’ or
‘low-meat-consumer’ comprises;
vegans,
lacto-(ovo)-vegetarians
and semi-vegetarians. All other
subjects were defined as omnivores
and most ate meat, fish, eggs and
dairy products on a daily basis.
particular interest. In addition, 116
schools were randomly selected
from the whole country for
inclusion in the study. Of the 116
randomly selected schools eight
had to be replaced since no
information on the students’
dietary intake at lunch was
available. The eight new schools
were randomly selected using the
same procedure as for the other
schools.
The participants in the Adolescent
Questionnaire Study (II, III) were
recruited during autumn 1996 from
Umeå and Stockholm in Sweden
and Bergen in Norway (Figure 4).
The Swedish subjects were
recruited by a random sample of
ninth-grade classes (15-16 year
olds) in municipal senior secondary
schools. Classes with more than 15
students were selected as the
sampling
unit,
rather
than
individuals, since the school setting
simplified data collection, and
improved the possibility of a high
response rate. Students from 22
classes in nine out of the ten
schools in Umeå, and 22 classes in
17 out of the 50 schools in
Stockholm were included. All
classes selected in Sweden and all
students present on the day of the
survey were willing to participate
in the study. In Bergen a random
Study samples
In the School Lunch Study (I) the
study sample was taken from the
total number of upper secondary
school students in Sweden, which
was 312 375 students in 19951996. The total sample was 75 210
adolescents in the 16-20 year old
age group eating school lunch in
124 Swedish secondary schools
(Figure 3). All eight municipal
upper secondary schools from
Umeå, Skellefteå, Sölvesborg and
Vänersborg were selected (Figures
3-4), since these towns were highly
influenced by the “Straight Edge”
philosophy which, because of its
emphasis on vegetarianism, was of
29
Subjects and methods
All (8) municipal schools from
Umeå, Skellefteå, Sölvesborg
and Vänersborg (7 840
students)
All Swedish upper
secondary schools
(312 375 students)
Eight schools randomly
selected as replacement
Eight schools with no
information was excluded
116 randomly selected
schools (67 370 students)
Sample of 124 schools
(75 210 students)
Figure 3 Sample procedures in the School Lunch Study, 1996.
sample of 11 schools was drawn
from a total of 24 schools in the
municipality.
Three
schools
refused to participate and were
replaced by a random selection of
three new schools from the
remaining 13. In total 2 041
students participated, 578 from
Umeå (response rate 95%), 504
from Stockholm (response rate
91%) and 959 from Bergen
(response rate 83%).
Umeå had 4 212 students in upper
secondary schools and the
adolescents were recruited by
advertisements and visits to
schools. The subjects had to be in
good health with no chronic
diseases and aged between 16 and
20 years. Thirty vegans were
recruited and thereafter 30
omnivores were matched by sex,
age (± 6 months) and height (± 3.5
cm). Of the 60 subjects
participating in the Nutritional
Assessment Study (V) 32 subjects,
selected at the end of year 1997,
conducted an energy expenditure
measurement with doubly labeled
water (IV).
In the Nutritional Assessment
Study (IV, V) the study sample
was taken from the municipality of
Umeå. At the time of the selection
in 1997-1998, the municipality of
30
Subjects and methods
Skellefteå (I)
(I)
Umeå (I-V)
Bergen (II, III)
Stockholm (II, III)
Vänersborg (I)
Sölvesborg (I)
Figure 4 Map of Nordic countries, indicating the study areas of papers I-V.
Ethics
The study was approved by the
Research Ethics Committee of the
Medical Faculty, Umeå University.
All participants (matrons and not
students in paper I) received verbal
as well as written information on
the purpose and the content of the
study and the participation was
voluntary. In the Adolescent
Questionnaire Study (II, III)
permission was obtained from the
school authorities and in Sweden
the principal of each school and
teacher of each class gave their
consent to the study. Each
participant in the Nutritional
Assessment Study (IV, V) gave
written informed consent.
Methods
School Lunch Study
In the School Lunch Study (I) a
telephone interview with the dining
hall matron of each school was
performed during March and April
in 1996. The matrons were asked
to give information about how
many students were eating vegan,
lacto-ovo-vegetarian or lacto-ovofish-vegetarian food at school
lunch.
Adolescent Questionnaire Study
In the Adolescent Questionnaire
Study (II, III), a questionnaire was
used to obtain information about
food and lifestyle related habits.
Each student was asked to
complete a questionnaire in a
31
Subjects and methods
classroom setting. A pilot-study
was performed in 1996 with 44
ninth-grade students from a village
close to Umeå and 30 ninth-grade
students in Bergen. The Swedish
questionnaire had 207 questions
and the Norwegian questionnaire
165 questions, and there were 106
identical
questions.
The
questionnaires were divided into
eight sections concerning:
diet for the 12 months preceding
the survey, and the questionnaire
asked
diet-related
questions
pertaining to that period of time.
Nutritional Assessment Study
Diet history
In the Nutritional Assessment
Study (IV, V) a diet history
interview was used to obtain
information about typical eating
patterns for the preceding three
months (Figure 5). The structure of
the diet history was elaborated in
two pilot interviews before being
conducted between August 1997
and June 1998. Twenty-eight of the
subjects, 14 vegans and 14
omnivores participated in the diet
history during the autumn semester
and 32 subjects (IV), 16 vegans
and 16 omnivores during the spring
semester to obtain seasonal
variations in dietary intake. The
reported food, beverage and dietary
supplement intakes were entered
into the dietary analysis program
“Stor MATs 4_03e”, which uses
the Swedish Food composition
data base (version 2_97). For
composite foods and dietary
supplements that were reported but
not listed in the food data base,
recipes and information on
nutritional content were entered. A
nutrient intake below the average
requirements (AR), according to
the NNR58 (Figure 1), was defined
as a nutrient intake indicating an
increased risk of deficiency in the
present thesis.
• Background information and
family structure (14 Swedish, 12
Norwegian questions).
• Food habits (84 Swedish, 71
Norwegian questions).
• Dental health (9 questions).
• Smoking and drinking habits (8
Swedish, 11 Norwegian questions).
• Physical activity (21 Swedish, 2
Norwegian questions).
• Attitudes to school (15 Swedish, 10
Norwegian questions).
• Relation to friends and family (19
Swedish, 13 Norwegian questions).
• Attitudes to diet and health (37
questions).
Answers to the food frequency part
of the questionnaire were used to
classify
subjects
as
either
vegetarians/low-meat-consumers
or omnivores, according to the
previously mentioned definitions.
Subjects
were
considered
vegetarian/low-meat-consumers if
they had followed a vegetarian like
32
PHYSICAL ACTIVITY ASSESSMENT (IV)
• 32 subjects.
• One interview per subject.
• Estimated physical activity during 14 days.
33
BLOOD SAMPLE
• 60 subjects.
• One sample for
vitamin D in
Nov-Dec 1998.
VALIDATION OF ENERGY (IV, V)
• 32 subjects got DLW.
• Seven urine samples per subject.
• Energy expenditure measurement during 14 days.
Figure 5 Study design of the Nutritional Assessment Study (IV, V), Umeå 1997-1998.
NUTRITIONAL ASSESSMENT (V)
• 60 subjects.
• Three fasting blood samples per subject.
• Assessment of iron, vitamin B12 and folate.
DIET HISTORY (IV, V)
• 60 subjects (1st in August 1997).
• Two 1-2h interviews per subject.
• Food intake of the preceding three months.
VALIDATION OF PROTEIN,
SODIUM AND POTASSIUM (IV, V)
• 60 subjects.
• Four 24-h urine collection per subject.
Subjects and methods
Subjects and methods
Validation of energy intake and
expenditure
After the diet history, validation of
protein, sodium and potassium, and
nutritional
assessment
were
completed,
total
energy
expenditure of 32 subjects (IV)
was measured during 14 days by
the DLW method (Figure 5)107.
Each subject collected three
baseline urine samples before
ingesting an oral dose of 0.12 g 2H
and 0.25 g 18O per kg estimated
body water96, 108. Single spot urine
samples were taken 24 h after the
dose was administrated and
thereafter on days 4, 8 and 14.
Carbon dioxide production rate
was calculated using a multipoint
method96 and the respiratory
quotient of the diet was taken as
0.85.
Validation of protein, sodium and
potassium intakes
After the subjects had participated
in the diet history interview (IV, V)
he/she started the first 24-h urine
collection (Figure 5). In total each
participant completed four 24-h
urine
collections
and
the
completeness of the collections
was verified using PABA92. Each
24-h urine collection was analysed
for PABA, nitrogen, sodium and
potassium. Sodium and potassium
in urine were determined by flame
atomic absorption spectrophotometry (Perkin Elmer model 5000),
according to routine clinical
laboratory procedures. Nitrogen in
urine was determined by the
Kjeldahl technique (Tecator 1002,
Perstorp Analytical, Bristol) and
PABA
was
measured
colorimetrically92. The biological
marker for sodium intake was
taken as sodium excretion in urine
and the biological markers for
nitrogen (protein) and potassium
intakes were taken as excreted
amounts divided by 0.81 for
nitrogen, 0.77 for potassium of
omnivores and 0.73 for potassium
of vegans. A linear regression
compensation method103 was used
for incomplete 24-h collections
with PABA recoveries between 5085%. Urine collections containing
85-110% of PABA were classified
as complete and those containing
less than 50% of PABA and over
110% of PABA were rejected.
34
Physical activity assessment
Physical activity interviews with
the 32 subjects were conducted
(IV) 14 days after ingestion of the
oral dose of DLW (Figure 5).
Respondents were questioned
about their physical activity during
the last two weeks, in a 30- to 60minute interview. The activities
were categorized according to six
activity grades with a given
definition and physical activity
ratio109; sleep (1.0), very light
activity (1.4), light activity (1.7),
moderate activity (3.0), heavy
activity (4.0) and very heavy
activity (6.0). A mean PAL was
then calculated and since PAL is
claimed to be independent of age,
Subjects and methods
weight and sex110 total energy
expenditure could be calculated by
multiplying PAL by the estimated
BMR.
iron deficiency anemia if P-iron
was <7.2 µmol/L (<40 µg/100mL),
TIBC was 73.4 µmol/L (410
µg/100mL), transferrin saturation
was <15%, and P-ferritin was <10
µg/L.
Nutritional assessments in blood
Three fasting venous blood
samples were taken one week apart
from 60 subjects (V). Hemoglobin,
S-ferritin, S-iron, TIBC, transferrin
saturation and immune cell
concentrations were measured in
all three blood samples to classify
the iron status as “normal”, “early
negative iron balance”, “iron
depletion”, “iron-deficient erythropoiesis” or “iron deficiency
anemia”, according to definitions
by Herbert111. A person was
classified as having an early
negative iron balance if plasma
iron (P-iron) was <21.5 µmol/L
(<120 µg/100mL), TIBC was
53.7–64.5
µmol/L
(300–360
µg/100mL), transferrin saturation
was 30%, and plasma ferritin (Pferritin) was <25 µg/L. A person
was classified as having iron
depletion if P-iron was <20.6
µmol/L (<115 µg/100mL), TIBC
was 64.5 µmol/L (360 µg/100mL),
transferrin saturation was 30%, and
P-ferritin was 20 µg/L. A subject
was classified as having irondeficient erythropoiesis if P-iron
was
<10.7
µmol/L
(<60
µg/100mL), TIBC was 69.8
µmol/L
(390
µg/100mL),
transferrin saturation was <15%,
and P-ferritin was 10 µg/L. A
person was classified as having
Vitamin B12 and folate was
measured in the first of the three
blood samples taken. A fourth
blood sample of the 60 subjects
was taken during November and
December 1998 for measurement
of
1,25-dihydroxy-D-vitamin
levels in serum. An adequate blood
concentration of vitamin B12,
folate, and 1,25-dihydroxy-Dvitamin was defined as a
concentration within the reference
interval used by the Clinical
Chemistry
Department,
The
University Hospital of Northern
Sweden, Umeå, Sweden. For Svitamin B12, the reference interval
of 95–568 pmol/L was used; for Sfolate, 3.4–47 nmol/L, and for S1,25-dihydroxy-D-vitamin, 26–156
nmol/L.
All blood samples were analyzed
according to standard methods
used at the Clinical Chemistry
Department,
The
University
Hospital of Northern Sweden,
Umeå, Sweden. Hemoglobin was
measured immediately on a
specimen collected into ethylenediaminetetracetic acid (EDTA)containing
tubes
using
cyanmethemoglobin
and
an
absorbance measurement. Iron was
35
Subjects and methods
measured by a colorimetric assay,
ferritin by an immunoturbidimetric
assay, and TIBC by an alkaline
buffer/reductant solution from
Roche Diagnostics, Indianapolis,
IN, USA. Vitamin B12 and folate
were analyzed by Quantaphase II
B12/Folate Radio Assay from
BioRad, Diagnostics Group, Alfred
Nobel Drive, Hercules, CA, USA.
A radio-isotopic assay and
chromatographic procedure from
Nichols Institute Diagnostics,
USA,
was
used
for
the
determination of 1,25-dihydroxyD-vitamin levels in serum, San
Juan Capistrano, CA, USA.
Statistical methods
Comparisons between dietary
groups and statistical analyses were
made by using the Mann-Whitney
U-test,
Pearson’s
chi-square,
Fisher’s exact test, the Wilcoxon
Signed Ranks Test and 2 factor
ANOVA (Table 3). A two-tailed
P-value of <0.05 was considered
statistically
significant.
All
statistical analyses were performed
using SPSS, versions 6.1, 9.0.1 or
10.0 (SPSS, Pty Ltd, Chicago, IL,
USA).
36
• … background and validation data…
• … the validity of the energy and protein intakes…
• … background and validation data, food and nutrient intake
and nutritional status…
• 2 factor ANOVA…
• Wilcoxon Signed Ranks Test…
• Mann-Whitney U-test…
IV
V
37
• … physical, health, family, social habit and exercise data…
• … physical, health, family, social habit, exercise, alcohol and
tobacco data…
• Mann-Whitney U-test…
• Pearson’s chi-square or Fisher’s
exact test for 2x2 tables…
III
Table 3 Statistical methods used in paper II-V.
Paper
Statistical method
… for comparisons of…
II
• Mann-Whitney U-test…
• … food consumption frequency…
• Pearson’s chi-square or Fisher’s
• … attitudes, dietary knowledge and meal habits…
exact test for 2x2 tables…
Subjects and methods
… vegans and omnivores of
each gender.
… vegans and omnivores of
each gender.
… between…
… dietary groups of each
gender and for each of the
vegetarian groups, as
compared with the omnivores.
… low-meat-consumers and
omnivores of each gender.
Results and discussion
RESULTS AND DISCUSSION
Subjects
compared with 251 girls and 342
boys living in Umeå, mean age
16.8 (range 15.9-18.2 years),112 and
concerning energy expenditure
compared with 374 Swedish 15year-old adolescents113.
The subjects in the Adolescent
Questionnaire Study may be
regarded as representative since
ninth grade is compulsory, and
since it was a random sample of
classes and schools and the mean
response rate was high (90%). Also
the internal response rate of each
question was high with >90% for a
majority of the questions. Classes
or schools, rather than individuals,
were used as sampling units, which
probably
reduced
precision
because of clustering, and it is
possible that there were differences
in ethical considerations between
classes or schools. However, the
schools selected were distributed
throughout the municipalities and
may, therefore, be regarded as
representative of senior secondary
schools.
The samples in the Adolescent
Questionnaire Study and the
Nutritional Assessment Study are
different
regarding
selection
method, number of subjects, what
was required of the subjects and
amount of information obtained. In
the Nutritional Assessment Study
the sample is less representative
than the sample in the Adolescent
Questionnaire Study. On the other
hand in the Nutritional Assessment
Study more was required of the
participants and the information
collected is, therefore, much more
detailed.
The subjects participating in the
Nutritional Assessment Study were
not random and might therefore not
be representative for the general
population. However, the subjects
were regarded as representative
concerning height, weight and
body mass index (BMI) when
The more detailed information
collected and the more required of
subjects participating in a study,
the higher the drop-out rate is most
likely to be, which will lead to a
less representative sample (Figure
6).
38
Results and discussion
•
•
•
Non-random selection.
Small number of subjects.
A lot required of the subject i.e.
high risk of drop-outs.
Less
representative
sample
Paper IV and V
More
representative
sample
•
•
•
Random selection.
Large number of subjects.
A little required of the subject
i.e. small risk of drop-outs.
Paper I, II and III
Figure 6 Factors with impact on how representative a sample will be, relevant to the papers in
the present thesis.
Prevalence of vegetarians
The School Lunch Study (I)
investigated how many students
aged 16-20 years were eating
vegetarian food at school lunch in
1996. Assuming that students
eating vegetarian food at school
lunch really are vegetarians, the
prevalence of vegetarians was
5.0% in Sweden (I) (Table 4). Two
percent were eating lacto-ovo-fishvegetarian food, 2.9% lacto-ovovegetarian food and 0.1% vegan
food. There was a higher
occurrence of students eating
vegetarian school lunches in the
town of Umeå (11.4%) than in
Sweden in general (5.0%).
old vegetarians in Umeå was
15.6% in 1996, compared with
4.8% in Stockholm and 3.8% in
Bergen (Table 4). In Umeå, lacto(ovo)-vegetarians (8.8%) were the
most common type of vegetarians
but in Stockholm and Bergen semivegetarians were more common
(2.6% and 2.3%, respectively).
There were a higher percentage of
females among vegetarians in
Umeå and Stockholm (P<0.01) but
no gender difference was found in
Bergen (Figure 7).
In the Adolescent Questionnaire
Study (II), the prevalence of
vegetarians was investigated by
classifying people as vegetarians
according to self-reported dietary
intake. The prevalence of 15-year39
1996
Questionnaire completed by subject, categorized 1996
by reported food intake.
Telephone interview with school matrons.
1996
Yeara
g
f
e
d
c
b
a
40
Questionnaire completed by subject, categorized 1996
by reported food intake.
Year when the study was conducted.
Number of people investigated.
SV = Semi-vegetarians.
LOV = Lacto-vegetarians and lacto-ovo-vegetarians.
V = Vegans.
All types of vegetarians: including SV, LOV, V.
Prevalence of students eating vegetarian school lunches.
Norway, Bergen (II)
Sweden, Stockholm (II) Questionnaire completed by subject, categorized 1996
by reported food intake.
Sweden, Umeå (II)
Sweden, Umeå (I)
Telephone interview with school matrons.
Sweden (I)g
g
Study design
Country, city
Table 4 Prevalence of young vegetarians in Sweden and Norway, 1996.
451
501
15.4
253
15.5
15.5
244
263
15.7
15.7
293
3 450
67 370
nb
15.6
16-20
16-20
Age
(years)
Results and discussion
male
female
male
female
male
female
mix
mix
Sex
2.2
2.4
0.8
4.1
0.8
6.1
2.2
2.0
SVc
(%)
1.4
1.3
1.2
2.5
4.6
13
7.1
2.9
LOVd
(%)
0
0.2
0.4
0.4
1.1
5.5
2.1
0.1
Ve
(%)
3.6
4.0
2.4
7.0
6.5
25
11
5.0
Allf
(%)
Results and discussion
Prevalence (%) of vegetarians
30
25
25
20
Females
15
10
Males
6.5
7.0
5
2.4
4.0 3.6
0
Umeå
Stockholm
Bergen
Figure 7 Prevalence (%) of 15-year-old vegetarian females and males in Umeå (Nfemales=293,
Nmales=263) and Stockholm (Nfemales=244, Nmales=253) in Sweden and Bergen (Nfemales=451,
Nmales=501) in Norway, 1996.
The information obtained in the
School Lunch Study concerns only
what was eaten for school lunch
and thus not what was eaten during
the rest of the day. There is a
possibility that some of the
adolescents were eating vegetarian
food at school lunch but
omnivorous food for other meals.
However, since students in most
cases (92%) had to notify the
matron that they would like
vegetarian food every day of the
semester, often by having a
certificate from a parent, school
nurse or doctor, it is likely that the
majority of the students were true
vegetarians.
The subjects in the Adolescent
Questionnaire
Study
were
classified into different dietary
groups based on the response to the
food frequency questions rather
than according to their own
perception. This provided a
measure of prevalence which
prevents misunderstanding of how
different types of vegetarians are
defined. Worsley et al 1998
concluded that the prevalence of
vegetarians became higher when
vegetarianism was self-reported
than if classified according to food
intake10. Sources of errors of
different methods used for
classifying vegetarians need to be
considered. The classification in
the Adolescent Questionnaire
41
Results and discussion
2001. However, the prevalence of
11% of students eating a vegetarian
school lunch is most likely not as
well correlated with the prevalence
of true vegetarians as the result in
the study of 1996. The reason for
this is that it has become more
common to serve a free-choice
vegetarian food alternative for both
vegetarians and omnivores at
school lunch. In 1996 only 14% of
the schools reported serving
vegetarian food for everybody,
compared with about half of the
schools participating in 2001. The
increased serving of free-choice
vegetarian food made it much more
difficult
for
the
matrons
interviewed in 2001 to give a valid
number
of
students
eating
vegetarian food who were also true
vegetarians. Therefore, the results
of the follow-up study most likely
overestimate the prevalence of
vegetarians. However, it can be
concluded that more vegetarian
food is eaten for lunch in Swedish
schools, since 98% of the schools
in 2001 serve vegetarian food at
school lunch, compared with 88%
of the schools in 1996 (I). An
increase in the number of schools
serving vegan food was also seen
from 27% in 1996 (I) to 64% in
2001.
Study relied on the response on
food intake of a limited number of
animal products. The major reason
for not including specific questions
about vegetarianism in the
questionnaire was due to the intent
to investigate adolescents in
general. This made it inappropriate
to ask questions specific to
vegetarians. Also the questionnaire
was very extensive. Instead of
calling the subjects vegetarians it
may be more correct to call them
low-meat-consumers. However, of
the 150 subjects that were defined
as low-meat-consumers 65 subjects
spontaneously noted at the end of
the questionnaire that they were
either vegan, lacto-vegetarian or
semi-vegetarian.
Few studies of the prevalence of
vegetarian adolescents in Sweden
have been made. To be able to
conclude that a change in
prevalence has occurred, studies
with similar design as well as
definitions of vegetarians need to
be compared. A journalist, A.
Asker, made a follow-up study in
2001, with the same methodology
as in the School Lunch Study20. Of
the 124 schools participating in
1996, 104 participated in the
follow-up study. In addition 19
other schools nearby the remaining
20 schools from 1996 were
included in the follow-up study.
The results of the follow-up
indicated that there was an increase
from 5% to 11% of students eating
vegetarian meals between 1996 and
42
The School Lunch Study found a
similar prevalence of vegetarians
(5%), as a Swedish questionnaire
study of 15-16 year-olds20. The
results of that study showed a
prevalence
of
5%
female
Results and discussion
vegetarians in Umeå (15.6%)
compared with Stockholm (4.8%)
and Bergen (3.8%) and a majority
were females (72.5%).
vegetarians and 3% males
vegetarians. Thus, both the
Swedish questionnaire study and
the Adolescent Questionnaire
Study (Figure 7) indicate a
relationship between gender and
vegetarianism, with young females
more often choosing vegetarian
food than young males. This agrees
with other previous studies, which
have reported that young as well as
adult females are more likely to be
vegetarians than young and adult
males4, 10, 18.
Food habits
The Adolescent Questionnaire
Study (II) investigated the food
habits
among
15-year-old
vegetarians and omnivores in
Umeå, Stockholm and Bergen.
Besides meat and other animal
products, female vegetarians less
often consumed potatoes, soft
drinks,
chips/peanuts,
cakes/cookies, fried and barbecued
food while more often consuming
rice/pasta, vegetables, coffee, tea,
microwave-heated food and dietary
supplements than did the female
omnivores (Table 5). However,
there was no difference between
the female groups in consumption
frequency of e.g. fruits/berries, ice
cream and sweets/chocolates. Male
vegetarians showed no major
differences
in
food
intake
compared with male omnivores,
except for eating animal products,
margarine,
ice
cream,
cake/cookies, and fried and
barbecued food less often (Table
5).
One of the reasons for the high
prevalence of vegetarians in Umeå
might be the active Straight Edge
music groups during the 1990s. For
example the Straight Edge
philosophy emphasizes vegetarianism and spreads its message
via music. Another reason may be
that the young vegetarians in Umeå
got a lot of publicity in the media
and there was an intense public
debate about vegetarianism, animal
welfare etc.
In conclusion, the prevalence of
adolescents aged 16-20 years
eating a vegetarian school lunch in
Sweden was 5% in 1996. There
was more than three times higher
prevalence
of
15-year
old
43
Results and discussion
1
2
3
4
5
6
7
*
**
***
4.6
4.3
3.7
5.5
0.7
4.2
18
5.2
35
7.5
11
15
3.4
20
24
2.6
6.1
4.4
6.2
2.1
7.6
9.7
3.2
1.6
6.8
5.1
7.4
13
6.1
15
9.5
7.4
2.1
Vegans
(n=22)
Female omn.
(n=880)
Female veg.
(n=108)
0***
0***
0***
2.7***
0.4*
3.2**
16**
3.3***
28**
5.1***
14***
12***
2.7*
32***
23
3.8
5.0
4.2
6.6
4.2*
15***
5.9***
1.7**
2.0
4.1***
5.4
5.9**
13
2.4
11***
4.1***
11*
6.2*
Lacto-(ovo)veg. (n=73)
5.7
5.5
4.4
5.9
1.0
5.4
17
5.8
42
8.3
10
16
5.0
17
17
3.8
11
6.5
7.6
5.1
7.6
16
2.3
2.2
9.9
7.6
10
15
12
17
12
9.6
1.9
Semi-veg.
(n=55)
0***
0***
0***
2.5***
0.4*
3.8**
17
6.4
35*
5.1*
9.5
14
5.0
25
19
3.3
9.7
6.5
6.3*
1.7
11
15
0.7
2.1
8.6
4.9**
7.2*
16
8.7
13*
5.1***
12
5.5
Omn. total
(n=1891)
Sausages
Pork chops/spare ribs/bacon
Poultry
Fish
Seafood (except fish)
Eggs
Cheese
Soft cheese
Milk
Sour milk and yogurt
Rice/pasta
Potatoes (boiled, baked, mashed)
Fried potatoes
Vegetables (except potatoes)
Fruits and berries
Porridge
Cereals
Bread (all kinds)2
Margarine3
Coffee4
Tea4
Soft drinks
Diet soft drinks
Alcoholic beverages
Chips, peanuts
Ice cream
Cakes, cookies
Sweets, chocolates
Fast foods
Fried food
Barbecued food5
Microwave-heated food6
Dietary supplements7
Male omn.
(n=976)
Food item
times/month1
Male veg.
(n=41)
Table 5 Food consumption frequencies of young vegetarians (veg.) and omnivores (omn.) in
Umeå, Stockholm and Bergen, 1996.
5.2
4.9
4.1
5.7
0.8
4.9
18
5.5
39
7.9
11
16
4.3
19
21
3.3
8.5
5.5
7.0
3.7
7.7
13
2.9
1.9
8.4
6.4
8.8
14
9.1
16
11
8.5
2.0
0***
0***
0***
7.2*
1.0
4.3
20
6.1
39
7.5
11
18
3.0***
25**
23
4.6
7.4
4.4*
5.5**
2.3
11
8.6**
1.3
1.7
4.3***
4.0**
4.5***
12
4.4**
13
6.4***
11
4.4*
0***
0***
0***
0***
0***
3.7**
18
3.9*
32**
4.7**
15***
9.3***
3.1**
31***
20
2.5**
6.1
5.0
6.5
4.5
13**
8.5***
1.6
1.9
5.5***
6.2
8.2
15
4.3
11***
3.0***
12
5.3***
0***
0***
0***
0***
0**
0***
0***
0***
0***
0***
14*
9.6**
4.7
37***
26
5.1
3.6*
5.1
7.8
3.1
22**
7.9*
0.9
2.8
7.0
4.9
3.6***
16
3.1
13
3.6***
11
12***
Unless otherwise indicated, figures show frequency rate (times/month) of consumption of a given
food item. Comparisons between dietary groups were made separately for both gender and for each
of the vegetarian groups, as compared with the omnivores, by the Mann-Whitney U-test.
The data given present slices of bread per day.
Grams per slice of bread.
Cups per month.
During the summer months.
Both ready foods that are bought in the supermarket and home-made food.
Number of pills per week.
Significantly different from omnivores (P≤0.05).
Significantly different from omnivores (P≤0.01).
Significantly different from omnivores (P≤0.001).
44
Results and discussion
legumes, vegetables, nuts/seeds,
juice, and dietary supplements and
a lower intake of cereals, ice
cream, and candy/chocolate than
the male omnivores.
Also it was shown that vegans (II)
consumed potatoes, cereals, soft
drinks,
cakes/cookies
and
barbecued food less often than did
omnivores (Table 5). They ate
rice/pasta and vegetables, drank tea
and took dietary supplements more
often than their omnivorous peers.
A methodological problem of a
food frequency questionnaire (II) is
that every single food item cannot
be included. Therefore, the result
that male vegetarians excluded
animal products without making
significant
changes
in
the
consumption frequency of other
food items may be explained by a
higher consumption of food items
not included in the questionnaire.
Our questionnaire illustrates the
conflict of interest between getting
enough detailed information on the
one hand, and not making a too
lengthy and tiresome questionnaire
on
the
other.
Another
methodological problem is that it is
usually more difficult to remember
what was eaten for subjects with
irregular food habits. In addition,
the format of the question/answer
categories may not be suitable for
subjects with irregular food habits.
Because the students were asked to
complete
an
extensive
questionnaire during a short time,
there is a risk that towards the end
they
were
becoming
less
focused114.
Young vegetarians (II) generally
wanted to find out more about
healthy eating than did the
omnivores and they preferred to
get the information from school
and the media. The stricter the
vegetarian diet the stronger was the
subject’s
wish
for
more
information on healthy eating.
The 16-20 year old vegan
adolescents in the Nutritional
Assessment Study (V) had a very
heterogeneous dietary intake. Food
groups, such as pizza/pies/pastries,
nuts/seeds,
cereals,
porridge,
coffee,
tea,
and
dietary
supplements, showed a high SD,
especially among female vegans.
The female vegans had a higher
intake of rice, legumes, vegetables,
whole-wheat bread, and dietary
supplements, and a lower intake of
ice cream, cake/cookies, and
candy/chocolate
than
female
omnivores (Table 6). The male
vegans had a higher intake of
45
Results and discussion
Table 6 Reported daily intake (g/day) of 30 vegans and 30 omnivores in Umeå, Sweden
1997–1998a.
FOOD GROUP (g/day)
FEMALES
MALES
Median (25th, 75th percentile)
Vegans
Omnivores
Vegans
Omnivores
(n=15)
(n=15)
(n=15)
(n=15)
Meat, and meat dishes
Fish, and fish dishes
Seafood, and seafood dishes
Eggs (not in food dishes)
Milk/sour milk/yogurt/cream
Cheese
Pizza/pies/pastries
Potatoes (not in food dishes)
Pasta/macaroni (not in food dishes)
Rice (not in food dishes)
Legumes
Vegetables (not potatoes)
Fruit/berries (not in food dishes)
Nuts/seeds
Cereals
Porridge
Whole-wheat bread
White bread
Butter/margarine
Coffee
Tea
Juice
Soft drinks/fruit drinks
Alcoholic beverages
Chips/popcorn
Ice cream
Cake/cookies
Candy/chocolate
Dietary supplements
a
*
**
***
0***
0***
0**
0***
0***
0***
12 (5, 25)
53 (24, 96)
83 (62, 96)
46* (21, 83)
255*** (136, 400)
292*** (167, 329)
128 (103, 322)
2 (0, 6)
0 (0, 16)
0 (0, 57)
103* (45, 143)
17 (6, 33)
15 (4, 28)
0 (0, 69)
40 (0, 181)
93 (45, 331)
237 (10, 275)
39 (0, 134)
4 (3, 11)
0***
7* (2, 33)
10* (6, 34)
1* (0, 7)
98 (78, 114)
14 (11, 25)
1.0 (0, 7)
4 (0, 6)
476 (416, 692)
26 (17, 37)
10 (5, 20)
52 (37, 87)
51 (36, 73)
21 (12, 27)
4 (0, 8)
90 (54, 139)
182 (132, 222)
0 (0, 2)
4 (2, 18)
14 (1, 36)
45 (16, 95)
45 (20, 87)
13 (10, 19)
0 (0, 21)
26 (0, 114)
13 (3, 103)
248 (213, 238)
26 (9, 151)
8 (5, 13)
11 (5, 24)
19 (11, 43)
37 (17, 70)
0 (0, 1)
0***
0***
0
0**
0***
0***
11 (0, 26)
125 (94, 142)
78 (54, 116)
72 (21, 113)
352*** (219, 401)
320*** (184, 404)
127 (49, 216)
5** (1, 11)
0* (0, 10)
32 (0, 71)
150 (93, 225)
87 (27, 199)
28 (27, 45)
0 (0, 0)
26 (0, 107)
148** (86, 411)
297 (0, 172)
29 (0, 172)
23 (10, 43)
0*** (0,0)
11 (7, 31)
21*** (12, 33)
1* (1, 6)
141 (120, 174)
24 (14, 34)
0 (0, 0)
2 (0, 6)
722 (564, 1176)
25 (16, 52)
11 (6, 31)
103 (60, 130)
63 (43, 100)
34 (23, 58)
11 (0, 16)
51 (19, 88)
72 (51, 136)
0 (0, 1)
25 (0, 53)
29 (7, 78)
51 (2, 266)
63 (18, 124)
19 (11, 43)
0 (0, 43)
7 (0, 69)
39 (0, 96)
284 (190, 508)
107 (5, 327)
7 (2, 43)
6 (3, 21)
20 (9, 45)
50 (35, 71)
0 (0, 1)
Data are given as medians (25th percentile, 75th percentile). Statistical comparisons between
groups with different diets were done using the Mann–Whitney U–test.
Significantly different from the data on same sexed omnivores (P<0.05).
Significantly different from the data on same sexed omnivores (P<0.01).
Significantly different from the data on same sexed omnivores (P<0.001).
Even
though
the
female
vegetarians
(II)
consumed
vegetables significantly more often
than the omnivores, the intake (32
times/month) was not as often as
might be expected of a vegetarian
population. The male vegetarians
(II) did not even eat vegetables
once a day (25 times/month).
Thirty-three percent of the
vegetarians (II), compared with
53% of 106 American vegetarians
aged 12-20 years (81% females),
reported eating vegetables more
than once a day28. Thirty-one
percent of the Swedish vegetarians
ate vegetables 6-7 times/week
while 27% of the American
46
Results and discussion
vegetarians
reported
eating
vegetables once a day. The
consumption frequency does not
give any information about the
amount of vegetables eaten, but the
vegans (V), both females and
males, showed a higher intake
(g/day) of vegetables compared
with omnivores. This confirms the
findings from Donovan and
Gibson’s study of Canadian 14-19
year-old adolescents where lactoovo-vegetarians had a higher intake
of vegetables than 29 omnivores27.
There was no significant difference
in fruit and berry consumption
among vegetarians (II) nor vegans
(V) compared with omnivores.
This was also shown by Donovan
and Gibson27 but does not verify
the results of the above mentioned
American study28, which showed
that vegetarians were twice as
likely to consume fruits.
Lower intake of candy and
chocolate (g/day) was seen among
vegans compared with omnivores
(V). The same was found by the
previously mentioned Canadian
and American study27, 28. However,
there were no statistical differences
in consumption frequency of candy
and chocolate among vegetarians
and omnivores (II).
The stricter the vegetarian diet, the
more often dietary supplements
were used (II). This finding is
consistent with the results of
another
questionnaire
study
comparing health practices of
vegetarians and omnivores115. A
higher
intake
of
dietary
supplements was also shown
among vegans compared with
omnivores (V). A possible
explanation for these findings is
that the stricter vegetarians are
more concerned about not getting
adequate amounts of nutrients from
their diet.
Lifestyle related
characteristics
In conclusion, the food habits of
vegetarians found in the present
studies (II, V) indicate that the
vegetarianism of adolescents in
Sweden may be a different
phenomenon
from
the
vegetarianism shown by previous
studies. This is indicated by the
fact that in our studies there was a
lower vegetable consumption
frequency than expected, and a
similar
fruit
consumption
frequency as the omnivores’.
In the Adolescent Questionnaire
Study (III) lifestyle related
characteristics of 2 041 low-meatconsumers and omnivores (15year-olds) from Umeå, Stockholm
and Bergen were compared. There
were no reported differences in
weight or calculated BMI between
low-meat-consumers
and
omnivores of either sex. Nor were
there any differences in time spent
on physical activity or level of
activity
(high/moderate/low)
(Table 7). The consumption
47
Results and discussion
common
among
low-meatconsumers as omnivores (III)
(Table 7). This is similar to what
was shown in an American
questionnaire study of 321 students
aged 12-20 years, which showed
that
physical
activity
(>3
times/week) was reported by 55%
of the vegetarians and 57% of the
omnivores, and alcohol and
tobacco use (at least weekly) by
23% and 22% respectively28. In
contrast to the results in the present
study (III), Slattery et al found
from interviews that young
American adults, eating meat or
poultry less than once a week,
reported more physical activity and
were less likely to drink alcohol
than omnivores116. Dwyer et al also
found that vegetarians aged 15-35
years were less likely to use
alcohol and tobacco117. The health
perception data reported by lowmeat-consumers (III) is in contrast
to the results of an American study,
which found that a larger number
of vegetarians than omnivores
strongly believed themselves to be
healthy115. These findings indicate
that
the
young
low-meatconsumers in the present study
have a different lifestyle compared
to findings from previous studies
of vegetarians, and that adherence
to a low-meat diet may not
correlate with other health
promotion
practices
among
adolescents in Sweden and
Norway.
frequency of alcoholic beverages
was similar among vegetarians (II)
(Table 5 and 7) and vegans (V)
(Table
6)
compared
with
omnivores of both genders.
However, the vegan males had a
lower intake (g/day) of alcohol
compared with male omnivores.
There was no difference in
frequency of smoking between
low-meat-consumers (III) and
omnivores but more female lowmeat-consumers used smokeless
tobacco (Table 7).
Female
low-meat-consumers
reported (III) more sick-days
during the previous year, attached
less importance to “being healthy“,
and believed they had the ability to
affect their own health to a greater
extent than female omnivores did
(Table 8). Female low-meatconsumers also reported more
often that they had been depressed
during the last week than did
female omnivores. Male low-meatconsumers reported more often
than male omnivores that they had
been tired without reason, often
had headaches, and had been
depressed during the last week.
There was no difference in
frequency of spending time with an
organization/club between lowmeat-consumers and omnivores.
Physical
activity,
alcoholic
beverage
consumption
and
smoking were reported to be as
48
Results and discussion
Table 7 Exercise data and alcohol and tobacco use of 15-year-old low-meat-consumers and
omnivores in Umeå, Stockholm and Bergen in 1996.
EXERCISE1
Female
Female
Male
Male
low-meatOmnivores low-meat- Omnivores
consumers
consumers
(n = 108)
(n = 880)
(n = 41)
(n = 976)
Physical activity (hours/week)2
2.9 ± 2.7
3.2 ± 3.0
4.8 ± 3.4
4.3 ± 3.5
Physical activity3
High (≥4h/week)
34
35
62
49
Moderate (2-3h/week)
26
28
18
25
40
37
20
26
Low (≤1h/week)
Alcoholic beverage3
Often (≥4/month)
20
15
15
18
Regularly (1-3/month)
28
33
23
26
Seldom (<1/month)
52
52
62
56
Smoking3
Daily
21
17
10
15
Sometimes
18
17
24
14
Never
61
66
66
71
Smokeless tobacco3
Daily
0*
0
12
5
Sometimes
10
2
17
14
Never
90
98
71
81
1
Comparisons between low-meat-consumers and omnivores were made separately for both
genders using Pearson’s chi-square and the Mann-Whitney U-test.
2
Mean ± S.D.
3
Response frequencies (%) of the different answer alternatives.
*
Results significantly different from those for omnivores (P<0.05).
49
Results and discussion
Table 8 Health data for 15-year-old low-meat-consumers and omnivores in Umeå, Stockholm
and Bergen in 1996.
HEALTH DATA1
Female
Female
Male
Male
low-meat- omnivores low-meat- omnivores
consumers
consumers
(n = 108)
(n = 880)
(n = 41)
(n = 976)
Sick-days during a year2
9.9* ± 12
8.3 ± 12
5.5 ± 6.3
6.6 ± 9.0
Perception of health3, 4
Very good / excellent
25
36
52
62
Good
45
40
44
27
Moderate
23
21
4
10
Poor
7
3
0
1
Importance of being healthy3, 4
Very important
64**
79
65
71
Quite important
27
18
31
22
Neither important nor unimportant
8
3
0
5
Unimportant
1
0
4
2
Ability to affect own health3, 4
Yes
94*
86
83
86
No
6
14
17
14
Tired without reason3-5
Yes
49
52
64*
42
No
51
48
36
58
Often have a headache3-5
Yes
37
34
38*
17
No
63
66
62
83
Sleep badly3-5
Yes
25
23
23
14
No
75
77
77
86
Unable to concentrate3-5
Yes
58
55
59
42
No
42
45
41
58
Stomach disorder3-5
Yes
22
23
32
15
No
78
77
68
85
Depressed3-5
Yes
54**
37
36**
14
No
46
63
64
86
1
Comparisons between low-meat-consumers and omnivores were made separately for both
genders using Pearson’s chi-square (or Fisher’s exact test for 2x2 tables) and the MannWhitney U-test.
2
Mean ± S.D.
3
Results pertain to Umeå and Stockholm, with 90 female low-meat-consumers, 447 female
omnivores, 23 male low-meat-consumers and 493 male omnivores.
4
Response frequencies (%) of the different answer alternatives.
5
During the last week.
*
Results significantly different from results for omnivores (P<0.05).
**
Results significantly different from results for omnivores (P<0.01).
50
Results and discussion
promotion
adolescents
Norway.
The
result
that
low-meatconsumers (III) did not spend time
with an organization/club more
often than the omnivores, verifies
the findings of another study
showing vegetarians not joining
clubs more often than others118.
The reason given in that study was
that vegetarians already were part
of a subculture that resides within
various other subcultures such as
the environmental movement.
However, Draper et al showed that
vegans are more likely to belong to
an organization directly connected
with their diet compared with other
types
of
vegetarians
and
29
omnivores . The explanation
given was their numerical minority
and that by joining an organization
they increased the possibility to
link up with like-minded people14.
The results of the present study
imply that many young low-meatconsumers are part of a subculture
and link up with like-minded
people in an unorganized way.
practices
among
in Sweden and
Validity of dietary intake
and energy expenditure
In the Nutritional Assessment
Study (IV, V) we compared the
validity of reported intakes of
energy, protein, sodium and
potassium, obtained from a diet
history method between 30 vegans
and 30 omnivores (Table 9).
Furthermore, a physical activity
interview method was validated
(IV) with the DLW method for 16
vegans and 16 omnivores. There
was no significant difference in
validity of reported energy intake
or energy expenditure between the
16 vegans and 16 omnivores (IV),
when using a diet history and
physical activity interview. The
following results are presented as a
mean value with a 95% confidence
interval. The diet history interview
had a bias towards underestimating
the energy intake [-1.93 MJ/day
(-2.89 to -0.97 MJ/day)], and the
physical activity interview had a
bias towards underestimating
energy expenditure [-1.44 MJ/day
(-2.37
to
-0.52
MJ/day)].
Furthermore, there was no
significant difference in validity of
reported protein intakes between
the dietary groups. The diet history
interview of 32 subjects (IV),
showed good agreement for
nitrogen (protein) intake and
In conclusion, young low-meatconsumers had physical activity,
smoked (III) and drank alcoholic
beverages (III, V) to the same
extent as the omnivores. The study
indicates that the lifestyle of young
low-meat-consumers differs from
the lifestyle found in previous
studies of vegetarians. Contrary to
findings from other studies,
adherence to a low-meat diet may
not correlate with other health
51
Results and discussion
agreement for reported nitrogen
and sodium intake and urinary
excretion of nitrogen and sodium.
The difference between reported
nitrogen intake and excreted
nitrogen was +0.31 g/day (-0.23 to
0.85 g/day) and the difference for
sodium was -198 mg/day (-538 to
141 mg/day). However, the diet
history method underestimated
potassium intake [-419 mg/day
(-689 to -149 mg/day)] compared
with the biological marker.
urinary nitrogen excretion, and the
difference was -0.40 g/day, (-1.10
to 0.29 g/day). The Nutritional
Assessment Study (V) with 59
subjects showed no significant
difference in the validity of
reported nitrogen or potassium
intake between the dietary groups.
However, for female vegans the
sodium excretion was higher than
sodium intake compared with
female omnivores (Table 9). The
diet history method showed good
Table 9 Validation of reported intakes of energy, nitrogen, sodium, and potassium in 30
vegans and 29 omnivores aged 16-20 years using the doubly labeled water method and 24-h
urine collections, in Umeå, Sweden 1997–1998a.
VALIDATION DATA
FEMALES
MALES
Vegans
Omnivores
Vegans
Omnivores
(n=15)
(n=15)
(n=15)
(n=14)
FILb
1.41 ± 0.39
1.56 ± 0.37
1.66 ± 0.21
1.71 ± 0.25
PALc
1.41* ± 0.22 1.84 ± 0.44
1.87 ± 0.39
2.05 ± 0.33
d
EIrep/EE mea
0.84 ± 0.25
0.92 ± 0.19
0.87 ± 0.19
0.85 ± 0.16
[Nrep x 0.81]/Nmeae
1.00 ± 0.32
0.98 ± 0.13
1.14 ± 0.27
1.04 ± 0.14
Narep/Nameaf
0.78* ± 0.42 1.02 ± 0.21
1.02 ± 0.32
1.15 ± 0.26
[Krep x 0.73 or 0.77] /Kmeag
0.90 ± 0.30
0.88 ± 0.19
1.02 ± 0.27
0.92 ± 0.18
a
Data are presented as means ± SD. The 2-factor ANOVA was employed with diet and sex as
the two factors for statistical comparisons between groups with different diets and sex.
b
Food Intake Level = reported energy intake divided by estimated basal metabolic rate.
c
Physical Activity Level = reported energy expenditure divided by estimated basal metabolic
rate of 32 subjects (16 vegans, 16 omnivores and 44% females).
d
Reported energy intake, of 32 subjects (16 vegans, 16 omnivores and 44% females) divided
by energy expenditure, as measured by the doubly labeled water method.
99
e
Reported nitrogen intake (Nrep) times the urine excretion factor of nitrogen 0.81 divided by
measured nitrogen in urine (Nmea).
f
Reported sodium intake (Narep) divided by measured sodium in urine (Namea).
g
Reported potassium intake (Krep) times the urine excretion factor of potassium, 0.73 for
100
vegans and 0.77 for omnivores divided by measured potassium in urine (Kmea).
*
Significantly different from the data on female omnivores (P<0.05).
52
Results and discussion
studies of different dietary methods
show that higher validity is
obtained
with
diet
history
compared with diet records when
used on adolescents (Table 10).
Thirdly, other dietary assessment
methods would be difficult to use
on adolescents, e.g. food records or
24h recalls, since these methods
require repetition, sometimes up to
20 days, in order to obtain good
individual estimates. Therefore
these methods may be too
troublesome and inconvenient for
many adolescents. In general, diet
histories have proven to yield the
most realistic energy intake
compared with other methods86.
The 32 subjects (IV) reported a
13% lower energy intake, 10.9 MJ
compared with the measured
energy expenditure 12.6 MJ
(P<0.05) (Table 9). Potassium
intake was underestimated by 7%
(P<0.05) while the nitrogen and
sodium intake showed good
agreement with 24-h urine
excretion.
A diet history method was chosen
rather than any other dietary
assessment method for three main
reasons. Firstly, the aim was to
obtain information on typical
eating patterns over a long time
period.
Secondly,
validation
Table 10 Comparison of different dietary methods food intake level (FIL) and physical
activity level (PAL) in studies of adolescents. Data is presented as mean ± standard deviation.
Dietary method
No.
Sex
Age
FILa
PALb
EIrep/EEmeac
subjects
F/M
(year)
Diet history89
5
F
18.0
1.69d
1.71d
1.01 ± 0.32
d
5
M
18.0
1.98
2.13d
0.94 ± 0.16
7-d food record89 5
F
18.0
1.31d
1.71d
0.77 ± 0.20
5
M
18.0
1.37d
2.13d
0.68 ± 0.31
7-d food record119 25
F
15.0
1.39 ± 3.30 1.79 ± 0.22 0.78 ± 0.16
25
M
15.0
1.56 ± 3.61 1.89 ± 0.16 0.82 ± 0.18
1.39d
1.78d
2w food record120 28 (nonobese) 14F, 14M 14.4
0.80 ± 0.19
d
27 (obese)
14F, 13M 14.7
0.80
1.57d
0.54 ± 0.23
a
Food Intake Level = reported energy intake/BMRest.
b
Physical Activity Level = measured energy expenditure/ BMRest.
c
Reported energy intake / Measured energy expenditure.
d
The basal metabolic rate used is based on mean age and weight of the subjects and calculated
from standard equations of Schofield 1985121.
53
Results and discussion
Bratteby et al reported no
significant bias in estimated energy
intake in validation studies of the
diet history method used on 15and 18-year-old subjects in the UK,
USA and Sweden122. However,
underestimation of energy intake
compared with energy expenditure
by the DLW method has been
shown repeatedly, ranging from
12% to 31%123, 124. The main
advantage with diet histories is that
it gives information on habitual
intake and thereby decreases the
problem with day-to-day variation.
Furthermore, it requires a fairly
limited effort by the subjects which
increases the possibility of
achieving a high co-operation rate,
compared with repeated recalls or
records. A disadvantage with the
diet histories is that they have a
high subjective impact because the
information is based on the
competence
of
the
person
performing the interview and the
subjects’ memory, cognition and
motivation in reporting true dietary
intake102. Other drawbacks are, that
irregular food habits may easily be
under- or overreported or forgotten,
and portion sizes may be under- or
overestimated.
collections with >110% PABA
recovery were rejected. The reason
for exclusion of collections with
<50% PABA recovery was that the
compensation method is not
recommended for cases of PABA
recovery levels below 50%. This
recommendation is due to the fact
that the probability of the subject
taking only two of the three PABA
tablets is greater below 50% PABA
recovery103. Furthermore, the
compensated part of the urinary
variable should not be larger than
the collected part, since it
potentially could cause too large an
error in the equation. The higher
exclusion limit of 110% PABA
recovery compared with 101% was
chosen since there are food items
common in the Swedish diet
containing benzoic acids. The
Swedish
National
Food
Administration has reported a 5002000 mg/kg of benzoic acid in
lingonberry, cloudberry (hjortron)
and arctic raspberry (åkerbär), and
smaller amounts (10 mg/kg) in
several other fruits and berries125.
Sour milk products and yogurts
containing jam with preserving
agent have also been found to
contain benzoic acid (100 mg/kg).
A large number of the 24-h urine
collections were incomplete (168
of 240 collections i.e. 70%) (V).
Only 40 collections i.e. 17% (IV,
V) were classified as complete and
25 (10%) collections with <50%
PABA recovery and 7 (3%)
In conclusion, diet history and
physical
activity
interviews
showed similar underestimation
and validity when used with young
vegans as when used with young
omnivores.
This
enables
54
Results and discussion
requirements for vegan males even
when
intake
from
dietary
supplements was included (Table
12, Figure 8). Only 65 % and 98%,
respectively, of the selenium and
calcium average requirements was
obtained
from
diet
and
supplements, respectively (Figure
8). The male omnivores had an
intake above average requirements
of all nutrients except one male
who had a lower intake (including
supplements)
of
selenium
compared
with
average
requirement (Table 12).
comparisons to be made between
the vegans and omnivores.
Dietary intake
The Nutritional Assessment Study
(V) investigated the dietary intake
by diet history of 30 vegans
compared with 30 omnivores. The
diet history showed that the vegans
had a lower dietary intake
(including supplements) than the
omnivores of protein, saturated fat,
cholesterol, disaccharides, niacin,
vitamin D, calcium, phosphorus,
and selenium (Tables 11-13). On
the other hand, they had a higher
intake than the omnivores of
energy from carbohydrates, and a
higher intake of polyunsaturated
fat, monosaccharides, dietary fiber,
vitamin C, vitamin E and
magnesium. In addition, the male
vegans had a lower intake than the
male omnivores of alcohol,
riboflavin, folate, sodium and zinc
(Tables 11 and 12). The female
vegans had a lower intake than the
female omnivores of total and
monounsaturated fat, and a higher
intake of vitamin B12 and folate
(Tables 11 and 13).
A large proportion of male vegans
had a lower intake than average
requirements for riboflavin and
vitamin B12 intake from diet, but
this proportion decreased if intake
from dietary supplements was
included (Table 12, Figure 8).
Calcium and selenium intakes from
diet
were
below
average
55
A significantly larger number of
female vegans had a lower dietary
intake (excluding supplements)
than average requirements of
vitamin A (6 subjects) and
riboflavin (10 subjects) compared
with female omnivores (Table 13).
A significantly larger number of
female vegans also had a lower
dietary intake of vitamin B12,
vitamin D and calcium, both when
including
and
excluding
supplements,
compared
with
average requirements (Table 13).
At group level the intake of
vitamin B12, vitamin D and calcium
from the diet of vegan females was
below average requirements but a
smaller proportion had an intake
lower than average requirements
when
intake
from
dietary
supplements was included (Table
13, Figure 9). The vegan females
had too low food intake of
selenium and 79% of the average
requirement was obtained from diet
Results and discussion
about half the intake in a typical
omnivorous diet. Good sources for
vegans are broccoli, soya beans,
enriched grains, algae, mushrooms.
However, vegans who are not
consuming whole or enriched
grains and green leafy vegetables
may obtain inadequate amounts of
riboflavin.
and supplements (Figure 9). The
selenium intake from diet alone
was
also
below
average
requirement (91%) for a large
proportion of female omnivores,
but intakes of all other nutrients
were above average requirements
at group level.
Vegetarians ate more dietary
supplements
than
omnivores
(Tables 5 and 6), and the
consumption increased the stricter
the vegetarian diet was. Several
other studies of vegetarians have
also shown a higher intake of
dietary supplements compared with
omnivores52, 115, 126. A large
proportion of the young vegans (V)
in the present study needed dietary
supplements of riboflavin, vitamin
B12, vitamin D, calcium and
selenium to obtain an intake above
the average requirements.
The dietary riboflavin intake was
below average requirement for 11
male vegans and 10 female vegans
(V). A study of 76 vegetarians
(mean age 27 years) showed that
73% of the males and 60% of the
females had a non-acceptable low
urinary riboflavin content40. A tenday diet record of 50 of these 76
vegetarians showed that the mean
riboflavin intake was 56% of the
recommended dietary allowance40.
Riboflavin is widely distributed
among the plant and animal
kingdom78. Although green leafy
vegetables are rich in riboflavin,
meat and dairy products supply
The vitamin B12 intake from diet
was insignificant among vegans
(V) since plant foods most often
lack the active form of vitamin B12.
Vegans have shown to be
dependent on supplements to get
an adequate intake60, 127. Most
vegans (80%) in the study ate, with
greater or lesser frequency, dietary
supplements containing vitamin
B12.
The dietary intake of vitamin D
among female vegans (V) was
below average requirement since
their diet did not include enough
plankton, certain mushrooms or
fortified vegan food items such as
soya drinks and margarines to add
up to 2.5 µg. There is no average
requirement given for vitamin D in
the NNR58, but a daily intake
above 2.5 µg has been shown to
prevent deficiency symptoms of
rickets and osteomalacia.
56
The low calcium intake of vegans
(V) compared with the average
requirement may be explained by
the vegans excluding dairy
products without replacing them
with enough calcium-rich vegan
Results and discussion
Concern has been raised among
parents and other adults about the
nutritional adequacy of the diet
when young vegetarians exclude
animal products without replacing
them with equally nutritious
vegetarian products132, 133. The
vegans in the present study (V)
were not “excluders” in a
consistent manner, since they were
well motivated and interested in
finding out about their diet and
health. But because of the small
non-random sample, we cannot
draw the conclusion that excluders
do not exist among the young
vegetarian population in Sweden.
food, such as calcium-fortified
soya drinks, legumes and some
green vegetables82. However, it is
likely that the average requirement
of calcium is higher for omnivores
than for vegans, since the higher
intake of protein and sodium in a
omnivorous diet increases the
amount of calcium lost in the
urine82, 128, 129.
A likely explanation for the low
intake
of
selenium
among
omnivores and vegans (V) is the
low content of selenium in the
Swedish soil and thus in Swedish
crops and animals. Another
explanation may be that the data of
selenium content in different food
items are underestimated. Reports
have shown that the selenium
content in beef and dairy products
is significantly higher than the
information given by the food
composition data base130, 131. The
latter explanation implies that there
is not a real low selenium intake
among omnivores.
In conclusion, the dietary intake of
vegans varied considerably and did
not comply with the average
requirements
for
riboflavin,
vitamin B12, vitamin D, calcium
and selenium intakes of a large
proportion of vegans. However,
this was compensated for by
dietary supplements for these
nutrients except calcium for males
and selenium for males and
females.
57
Results and discussion
Table 11 Reported intake of macronutrients including supplements. Mean ± SD of 30 vegans
and 30 omnivores aged 16-20 years in Umeå, Sweden 1997–1998a.
ENERGY AND
FEMALES
MALES
MACRONNRb Vegans Omnivores NNRb
Vegans Omnivores
NUTRIENTS
(n=15)
(n=15)
(n=15)
(n=15)
13.9e 12.2 ± 1.7 13.2 ± 2.0
Energy (MJ)
9.6c 8.9 ± 2.18
9.5 ± 2.0
11.2d
15.7f
***
51 73***± 14 120 ± 22
Protein (g)
47 55 ± 17
80 ± 18
g
10–15 10***± 1.0 15 ± 1.7
E% protein
10–15 10***± 1.5
14 ± 1.3
*
100 88 ± 15
Fat (g)
73 58 ± 23
75 ± 22
100 ± 22
<30 27 ± 2.6
E% fatg
<30 24***± 5.5
30 ± 3.8
29 ± 4.2
Carbohydrates (g)
310 340 ± 79
430 460 ± 66 426 ± 75
310 ± 62
55–60 63***± 3.2 55 ± 4.0
E% carbohydratesg
55–60 66***± 5.3
56 ± 3.8
Alcohol (g)
14 3.9 ± 4.4
19 2.1*± 3.1 7.0 ± 7.9
4.9 ± 7.0
g
E% alcohol
<4.5 1.4 ± 1.6
<4.5 0.5*± 0.7 1.6 ± 1.8
1.6 ± 2.3
***
<33 25***± 5.5 46 ± 9.3
Saturated fat (g)
<24 15 ± 6.8
34 ± 10
*
42 32 ± 6.5
Monounsaturated fat (g)
30 20 ± 12
27 ± 8.0
37 ± 8.7
25 21***± 3.8 12 ± 3.7
Polyunsaturated fat (g)
18 15***± 6.5
8.6 ± 2.9
–
Cholesterol (mg)
– 2.3***± 2.4 230 ± 76
2.1***± 2.9 330 ± 58
*
–
Monosaccharides (g)
– 65 ± 28
48 ± 16
64**± 19
47 ± 17
**
–
Disaccharides (g)
– 72 ± 29
100 ± 29
77***± 20 140 ± 40
Sucrose (g)
54 69 ± 28
75 73 ± 21
69 ± 22
88 ± 36
***
38
Dietary fiber (g)
28 34***± 11
21 ± 6.3
44 ± 10 25 ± 8.0
a
Data are given as mean ± SD. Statistical comparisons between groups with different diets
were done using the Mann–Whitney U–test.
b
Recommended intake according to the Nordic nutrition recommendations 199658 except
for energy.
c
Energy expenditure (MJ), as measured by the doubly labeled water method, of seven of the
female vegans.
d
Energy expenditure (MJ), as measured by the doubly labeled water method, of seven of the
female omnivores.
e
Energy expenditure (MJ), as measured by the doubly labeled water method, of nine of the
male vegans.
f
Energy expenditure (MJ), as measured by the doubly labeled water method, of nine of the
male omnivores.
g
Percent of total energy intake that is energy derived from protein, fat, carbohydrates or
alcohol respectively.
*
Significantly different from the data on same sexed omnivores (P<0.05).
**
Significantly different from the data on same sexed omnivores (P<0.01).
***
Significantly different from the data on same sexed omnivores (P<0.001).
58
***
**
*
e
d
c
b
a
59
Average requirements, according to the Nordic nutrition recommendations. Average requirement of vitamin D was taken as 2.5 µg and lowest recommended intake was used for
vitamin E and potassium.
Statistical comparisons were employed using Pearson’s chi-square test between groups with different diets, of number of subjects below average requirements.
Retinol equivalents.
Niacin equivalents.
Alpha tocopherol equivalents.
Significantly different from the data on same sexed omnivores (P<0.05).
Significantly different from the data on same sexed omnivores (P<0.01).
Significantly different from the data on same sexed omnivores (P<0.001).
Table 12 Dietary intake (mean ± SD) of vitamins and minerals of 15 male vegans and 15 male omnivores, in Umeå, Sweden 1997–1998.
Micronutrient
ARa
No. < ARa, b (excluding supplements) No. < ARa , b(including supplements)
Mean ± SD (including supplements)
intake of males
Vegans
Omnivores
Vegans
Omnivores
Vegans
Omnivores
(n=15)
(n=15)
(n=15)
(n=15)
(n=15)
(n=15)
750
2
0
2
0
Vitamin A (RE)c
1080 ± 264
1280 ± 365
Thiamine (mg)
1.1
3
0
2
0
2.9 ± 2.0
2.4 ± 0.7
Riboflavin (mg)
1.4
11***
0
4
0
2.3** ± 1.9
3.0 ± 0.9
15
3
0
0
0
Niacin (NE)d
34*** ± 7.8
48 ± 9.5
Vitamin B6 (mg)
1.3
0
0
0
0
3.6 ± 1.2
3.2 ± 0.9
1.4
15***
0
4
0
Vitamin B12 (µg)
22 ± 35
6.4 ±1.3
140
0
0
0
0
Folate (µg)
633*** ± 158
944 ± 2460
Vitamin C (mg)
30
0
0
0
0
226*** ± 61
113 ± 44
2.5
2
0
0
0
Vitamin D (µg)
4.9*** ± 1.9
8.6 ± 2.5
4.0
0
0
0
0
Vitamin E (α-TE)e
21*** ± 5.4
11 ± 4.6
Iron (mg)
8.5
0
0
0
0
22 ± 6.7
20 ± 8.1
Calcium (mg)
600
12***
0
10***
0
592*** ± 189
1700 ± 443
Phosphorus (mg)
450
0
0
0
0
1370*** ± 288
2180 ± 408
Magnesium (mg)
–
572* ± 100
462 ± 112
Sodium (mg)
–
3800* ± 856
4660 ± 1110
Potassium (mg)
1600
0
0
0
0
4200 ± 864
4100 ± 696
Zinc (mg)
5
0
0
0
0
14* ± 6.4
18 ± 6.1
30
15***
2
11***
1
Selenium (µg)
23*** ± 14
47 ± 17
Results and discussion
***
**
*
e
d
c
b
a
60
Average requirements, according to the Nordic nutrition recommendations. Average requirement of vitamin D was taken as 2.5 µg and lowest recommended intake was used for
vitamin E and potassium.
Statistical comparisons were employed using Pearson’s chi-square test between groups with different diets, of number of subjects below average requirements.
Retinol equivalents.
Niacin equivalents.
Alpha tocopherol equivalents.
Significantly different from the data on same sexed omnivores (P<0.05).
Significantly different from the data on same sexed omnivores (P<0.01).
Significantly different from the data on same sexed omnivores (P<0.001).
Table 13 Dietary intake (mean ± SD) of vitamins and minerals of 15 female vegans and 15 female omnivores, in Umeå, Sweden 1997–1998.
a
a, b
a ,b
Micronutrient
Mean ± SD (including supplements) AR No. < AR (excluding supplements) No. < AR (including supplements)
intake of females
Vegans
Omnivores
Vegans
Omnivores
Vegans
Omnivores
(n=15)
(n=15)
(n=15)
(n=15)
(n=15)
(n=15)
6*
1
5
1
Vitamin A (RE)c
1030 ± 698
1330 ± 713 700
Thiamine (mg)
0.9
3
0
3
0
3.6 ± 6.4
1.8 ± 0.6
Riboflavin (mg)
1.1
10**
1
5
1
3.3 ± 6.4
2.2 ± 0.9
12
4
3
1
0
Niacin (NE)d
26* ± 8.4
33 ± 10
Vitamin B6 (mg)
1.0
0
0
0
0
4.5 ± 6.6
2.3 ± 0.9
1.4
15***
0
8**
0
Vitamin B12 (µg)
17* ± 41
5.4 ± 2.7
120
0
1
0
1
Folate (µg)
577*** ± 263
251 ± 130
Vitamin C (mg)
30
0
0
0
0
197*** ± 100
127 ± 91
2.5
11***
0
7**
0
Vitamin D (µg)
3.6* ± 2.8
6.0 ± 2.7
3.0
0
0
0
0
Vitamin E (α-TE)e
17*** ± 7.7
15 ± 3.0
Iron (mg)
10
2
5
2
4
18 ± 9.0
15 ± 9.6
Calcium (mg)
11***
0
10***
0
741*** ± 711
1330 ± 372 600
Phosphorus (mg)
0
0
0
0
1040*** ± 306
1540 ± 378 450
Magnesium (mg)
–
453** ± 121
332 ± 92
Sodium (mg)
–
2590 ± 986
3040 ± 614
Potassium (mg)
0
0
0
0
3460 ± 1240
3160 ± 921 1600
Zinc (mg)
5
1
0
1
0
11 ± 6.5
12 ± 4.3
30
15
11
11
11
Selenium (µg)
24* ± 22
35 ± 36
Results and discussion
50
100
150
200
0
100
150
200
61
Figure 8 Nutritional intakes from diet and supplements, as percentage of average requirements of 16-20 year olds a) 15 male vegans and b) 15 male
omnivores. Average requirement of vitamin D was taken as 2.5 µg and lowest recommended intake was used for vitamin E and potassium57, 58. The
intakes of the nutrients that reaches 200% of the average requirements indicates that the intakes were above 200% of average requirements.
Percent (%) of average requirement
50
b) Male omnivores
From supplements.
From diet.
Thiamine
Vitamin A
Thiamine
Vitamin A
Percent (%) of average requirement
Niacin
Riboflavin
Riboflavin
Vitamin B6
Vitamin B6
Niacin
Folate
Vitamin B12
Vitamin C
Vitamin C
Vitamin B12
Vitamin D
Vitamin D
Folate
Iron
Calcium
Vitamin E
Calcium
Phosphorus
Vitamin E
Phosphorus
Potassium
Iron
Zinc
Potassium
Zinc
0
Selenium
Selenium
a) Male vegans
Results and discussion
50
100
150
Vitamin D
Vitamin C
Folate
Vitamin B12
Vitamin B6
Vitamin D
Vitamin C
Folate
Vitamin B12
Vitamin B6
Thiamine
Vitamin A
0
100
150
Percent (%) of average requirement
50
b) Female omnivores
200
62
Figure 9 Nutritional intakes from diet and supplements, as percentage of average requirements of 16-20 year olds a) 15 female vegans and b) 15
female omnivores. Average requirement of vitamin D was taken as 2.5 µg and lowest recommended intake was used for vitamin E and potassium57, 58.
The intakes of the nutrients that reaches 200% of the average requirements indicates that the intake were above 200% of average requirements.
From supplements.
From diet.
Thiamine
Vitamin A
Riboflavin
Percent (%) of average requirement
Niacin
Riboflavin
Niacin
200
Iron
Calcium
Vitamin E
Calcium
Phosphorus
Vitamin E
Phosphorus
Potassium
Iron
Zinc
Potassium
Zinc
0
Selenium
Selenium
a) Female vegans
Results and discussion
Results and discussion
Biochemical markers of
nutritional status
Iron
Female vegans (V) had a higher
hemoglobin concentration than
female omnivores, but there was no
difference in the S-ferritin level
(Table 14). Among males there
were none insufficient iron stores
but the prevalence of low iron
stores among females was 20% for
vegans and 23% for omnivores.
These results are in contrast with a
study of 79 lacto-ovo-vegetarians
(14-19 years) showing a higher
number of vegetarians (29%) with
low plasma ferritin (<12µg/L)
compared with omnivores (17%)75.
Similar results are shown in
another study of 35 vegetarians and
32 omnivores (mean age 23 years)
which showed that 6 vegetarians
and 1 omnivore were anemic134.
Despite the intake of low absorbed
iron and a high intake of dietary
fiber and possibly phytate, the
vegans in the present study (V) had
similar iron status as the
omnivores, which confirms the
findings of other studies71, 73, 135, 136.
Thus, there are conflicting results
regarding iron status of vegetarians
compared with omnivores.
The iron in a vegan diet is
nonheme
with
a
lower
bioavailability than the heme-iron
in an omnivorous diet. However,
the female vegans (V) were shown
to have a higher nutritional density
of iron in their diet compared with
omnivores and also a higher
density of vitamin C. This may
partly explain why there was no
difference in iron status between
vegan and omnivores. A study in
Australia showed that all iron
consumed by vegetarians was
nonheme-iron
and
for
the
omnivores 90% was nonhemeiron137.
Research
indicates
nonheme-iron absorption from a
lacto-ovo-vegetarian diet to be
70% lower than from an
omnivorous diet, but an associated
decrease in fecal ferritin excretion
suggests a physiological adaptation
to increase the efficiency of iron
absorption138.
63
16 ± 6.0
67 ± 8.4
25 ± 11
30 ± 30
452 ± 208
10 ± 4.1
101 ± 39
15 ± 5.4
60* ± 7.7
26 ± 9.1
24 ± 15
287** ± 220
23** ± 10
122 ± 34
7.0–27
35–70
20–50
10–82
96–568
3.4–47
26–156
Serum iron (µmol/L)
TIBC (µmol/L)c
Transferrin saturation (%)
Serum ferritin (µg/L)
Serum vitamin B12 (pmol/L)
Serum folate (nmol/L)
Serum 1,25-dihydroxy-
26–156
3.4–47
96–568
10–200
20–50
35–70
9.0–32
135–168
107 ± 026
18*** ± 6.6
196*** ± 91
56 ± 24
32 ± 7.7
60 ± 5.4
19 ± 4.2
148 ± 7.5
91 ± 23
12 ± 8.1
443 ± 149
61 ± 32
34 ± 7.9
57 ± 3.5
19 ± 4.5
146 ± 6.9
64
D–vitamin (pmol/L)
a
Data are given as means ± SD. Statistical comparisons between groups with different diets were done using the Mann–Whitney U–test.
b
According to the Clinical Chemistry Department, The University Hospital of Northern Sweden, Umeå, Sweden.
c
Total iron binding capacity.
*
Significantly different from the data on same sexed omnivores (P<0.05).
**
Significantly different from the data on same sexed omnivores (P<0.01).
***
Significantly different from the data on same sexed omnivores (P<0.001).
120 ± 7.4
127* ± 5.0
119–153
FEMALES
MALES
Reference rangeb Vegans (n=15) Omnivores (n=15) Reference rangeb Vegans (n=15) Omnivores (n=15)
Hemoglobin (g/L)
NUTRITIONAL DATA
Table 14 Nutritional assessment in blood of 30 vegans and 30 omnivores aged 16-20 years, in Umeå, Sweden 1997–1998a.
Results and discussion
Results and discussion
Vitamin B12
The vegans (V) had an average
serum concentration of vitamin B12
within the reference range (Table
14). Three out of 30 vegans (V)
had
serum
vitamin
B12
concentration lower than the
reference range, which is a lower
prevalence than found in other
studies52, 65. A study of 93
Australian vegetarians (mean age
29 years) showed that 15 had
serum vitamin B12 levels below
normal65. None of the vegetarians
were vegans and the subjects had
practiced their diet for a mean of
7.3 years. Another study of 36
Canadian
lacto-ovo-vegetarians
(mean age 27 years) showed that
almost one third of them had serum
vitamin B12 levels below the lower
limit of normality52. It was also
found that 9 of the 10 vegetarians
with low vitamin B12 levels in that
study had been vegetarians for
more than three years. The vegans
in the present study (V) had been
vegans for 1.7 years (range 0.5-3.5
years) and vegetarians for 2.8 years
and the comparatively low
prevalence of low vitamin B12
serum levels could probably partly
be explained by the subjects’ few
years as vegans and the use of
vitamin B12 supplements. Two of
the vegans classified as having low
vitamin B12 concentrations in the
present study (V) did not take any
supplements. One did, which
indicates an absorption problem
caused by e.g. lack of intrinsic
factor rather
intake14, 23.
than
inadequate
In early B12 depletion, a low level
of the vitamin is seen in serum.
However, a lower serum level than
normal does not necessarily
indicate deficiency. The next stage
is a decrease in stores of vitamin
B12 in the body’s cells, for example
the red blood cells. This stage of
vitamin B12 depletion may be
followed by biochemical changes,
such as rise in methylmalonic acid
in the blood. Finally, clinical
symptoms
of
vitamin
B12
deficiency
and
megaloblastic
anemia occur. However, among
vegans neurological symptoms139
are more likely to occur before
symptoms of anemia since most
often vegans have a high
consumption of folate that protects
them from anaemia139, 140. In diets,
where folate intake is adequate,
lowered vitamin B12 intake leads to
depleted plasma vitamin B12
concentrations with a concomitant
increase
in
homocystein
141
concentration . The detection of
increased homocystein levels is a
way to determine vitamin B12
deficiency.
65
Vitamin D
The vegans (V) had an average
serum concentration of 1,25dihydroxy-D–vitamin within the
reference range (Table 14). The
dietary intake of vitamin D was
lower among vegans compared
Results and discussion
(20%) as among female omnivores
(23%). Three vegans had low
serum vitamin B12 levels but
further analyses are needed to be
able to conclude that vitamin B12
deficiency exists among them.
Serum 1,25-dihydroxy-D–vitamin
levels were adequate for both
vegans and omnivores but this does
not exclude a possible inadequate
vitamin D status.
with
omnivores,
but
they
presumably
obtained
enough
vitamin D from supplements and
via endogenous production for the
conversion of 25-dihydroxyvitamin
D to sufficient levels of 1,25dihydroxy-D–vitamin. However,
we cannot exclude the possibility
that some of the vegans may have
inadequate vitamin D status since
serum 25-dihydroxyvitamin D
levels were not measured.
General discussion
The concentration of serum 25hydroxyvitamin D is the most
accurate measure of vitamin D
status, since 1,25-dihydroxy-Dvitamin may be normal in a
vitamin D deficient state105. The
serum 1,25-dihydroxy-D-vitamin
concentration is, however, often
used in Swedish clinical work to
monitor the vitamin D status of
patients with chronic renal failure
and distinguish between vitamin Ddependent and vitamin D-resistant
rickets142. Before vitamin D
supplementation of some food
items was started in the 1940s,
vitamin D deficiency was fairly
common in the Scandinavian
countries143. A recent study
showed that female omnivores (915 years) living at high latitude,
where there is only little sunlight in
the winter, had a high prevalence
(13.4%) of severe hypovitaminosis
D in midwinter (FebruaryMarch)143.
In conclusion, low iron stores was
as common among vegan females
Vegetarianism can be seen as a
dietary fad, an ethical choice or a
political statement. Therefore
eating vegetarian food may not
necessarily mean having a healthy
diet, as well as eating omnivorous
food may not always be adequate
for all nutrients. It all depends on
what foods and amounts are
included in the diet. It is important
for adolescents in general and
vegetarians in particular to receive
more knowledge, both theoretical
and practical, about how to
combine and prepare a healthy diet.
Schools and parents have an
important role to play by
increasing knowledge and make
well-planned food available. The
present interest in vegetarianism
among adolescents is a great
opportunity
to
fulfil
this
assignment
among
both
vegetarians and omnivores.
The papers in this thesis provide
information which indicates that
the new generation of vegetarians
66
Results and discussion
suggests that healthy vegetarianism
improves health.
have different dietary and lifestyle
habits compared with what
previous studies of vegetarians
have shown. For vegetarian
adolescents, especially vegans, it is
essential to be well motivated and
take an active interest in the new
dietary regime, and to appreciate
the fact that it is not simply a
matter of excluding food items.
Excluded animal products should
be replaced with equally nutritious
vegetarian products. If there is no
interest in nutrition and no
nutritious vegetarian food available
at home or in school, a poor eating
pattern may be the consequence.
Some schools choose not to serve a
vegan lunch alternative for various
reasons, but vegans will most
likely not stop eating vegan food
just because it is not served for
school lunch. Rather, the vegan
will probably eat a less nutritious
lunch or nothing at all. It is
possible for young vegans to have
an adequate dietary intake, but
vitamin B12 supplements are
needed and care needs to be taken
to ensure sufficient intake of
nutrients, especially selenium and
calcium. More over, research
This thesis has contributed with
new valuable knowledge about
young vegetarians and omnivores,
but there is still much more to find
out. One interesting area for
research is studies on long-term
effects of, for example, the risk of
osteoporosis. The vegans in the
present thesis showed a lower
intake of calcium, and the energy
expenditure indicated less physical
activity compared with omnivores,
which may result in a lower bone
mineral density. To monitor the
prevalence
of
vitamin
B12
deficiency in long-term vegetarians
is also of high priority. Therefore,
biochemical analyses of B12, folate,
homocystein and methylmalonic
acid should be performed to be
able to establish the causes of a
possible deficiency. Iodine is also a
nutrient interesting to study among
vegans since dietary sources are
limited, especially if iodinated salt
is not used. Another aspect of great
interest is to understand the
motives of young people for
adopting vegetarianism.
67
Conclusions
CONCLUSIONS
The prevalence of adolescents (16-20 years) eating vegetarian food at
school lunch was 5% in Sweden 1996. There was a much higher
occurrence of adolescents eating vegan food (2%), lacto-ovo-vegetarian
food (7%) and lacto-ovo-fish-vegetarian food (2%) in the town of Umeå
compared with Sweden overall (I).
There was a significantly higher prevalence of 15-year-old adolescent
vegetarians in Umeå (15.6%) compared with Stockholm (4.8%) and
Bergen (3.8%) in 1996. A high proportion of the adolescents choosing a
vegetarian dietary regime were females (72%) (II).
Even though the female vegetarians (15 year olds) consumed vegetables
significantly more often than the omnivores, the intake (32 times/month)
was not as often as might be expected of a vegetarian population. The
male vegetarians reported eating vegetables not even once a day (25
times/month). There was no difference between the intake of fruits/berries,
sweets/chocolates and fast foods by vegetarians compared with omnivores
(II). However, female vegetarians more often than female omnivores
consumed dietary supplements.
The lifestyle of young low-meat-consumers differs from the lifestyle
shown in previous studies of vegetarians, as they reported being less
healthy and having similar exercise, alcohol consumption, smoking
frequency and tobacco use as the omnivores. Contrary to findings from
other studies, adherence to a low-meat diet may not correlate with other
health promotion practices among adolescents in Sweden and Norway
(III).
There was no significant difference in the validity of reported energy
expenditure or energy and protein intakes between vegans and omnivores
when using physical activity and diet history interviews. This indicates
that it is possible to make a comparison between the vegans and omnivores
(IV).
68
Conclusions
Young vegans had a higher calculated intake than young omnivores of
vegetables, legumes, and dietary supplements, and a lower intake of ice
cream, cake/cookies, and candy/chocolate. Vegans had a higher
prevalence of dietary intakes below average requirements of riboflavin,
vitamin B12, vitamin D, calcium and selenium compared with omnivores.
Average intakes of calcium and selenium remained below average
requirements even after inclusion of intake from dietary supplements (V).
There was no difference in iron status among young vegans and
omnivores, 20% of the vegans and 23% of the omnivores had low iron
stores. Both vegans and omnivores had adequate levels of 1,25-dihydroxyD–vitamin but three out of 30 vegans had low vitamin B12 concentration in
blood (V).
69
Acknowledgements
ACKNOWLEDGEMENTS
This thesis is not the result of one person’s work. On the contrary a lot of
people have contributed in one way or another to bring this work to what it is
today. I am grateful to all of you. In particular I wish to express my sincere
and warm gratitude to the following:
Gunnar Johansson without whom this project would not have been
possible. Thank you for introducing me to vegetarian research, for
invaluable scientific tutoring and for sharing your knowledge.
Brittmarie Sandström for excellent guidance and professional advice.
Charlotte Nygren for constructive support and for your trust in my ability.
Ola Haugejorden, Kristin Klock, Anne Nordrehaug Åström and Klaas
Westerterp for fruitful feedback on the manuscripts.
Ulla Rönnlund for being a wonderful mentor. It has been a privilege to
work with you.
Agneta Hörnell for fruitful feedback and constructive advice during the
final part of this thesis.
Seppo Salonen for skilful computer help and never ending patient
support.
Linda Hagfors for valuable help regarding data entry and for creating a
warm atmosphere in our room.
Teachers and staff at the Department of Food and Nutrition: To each one
of you I wish to express my deepest appreciation for your friendship and
encouragement.
AB PT Datatech Systems Sweden for professional computer support and
for undertaking the hard and challenging work with solving our Teleform
problem.
Elisabet Forsum for generously introducing me to the world of doubly
labeled water technique.
70
Acknowledgements
Allan Hackett for your wonderful support and reading the manuscripts
during my stay in Liverpool.
Lars Dahlgren for fruitful discussions about qualitative methods and for
showing interest in our work. I look forward to our continuing
collaboration.
Maria Hedström, Maria Larsson, and Inger Öhlund for valuable help
regarding data entry.
All the participating subjects, without whom this project would not have
been possible, for showing interest and donating your time.
Bertil Winther for proofreading my first paper and inspiring me to learn
more about the American language.
My family Gunnel and Ingvar Larsson, Marita, Helge, Elina and Filip
Winther for your never-ending support and encouragement during all
these years. Even though you were far away you were always close at
heart.
Last but not least, my deepest gratitude goes to my partner Peter
Tanskanen for standing by my side and providing me with support when
times were tough. "May you sail on the sea of success, and land on the
shore of happiness".
Financial support for this work was given by the Faculty of Social Sciences,
Umeå University, the Swedish Foundation for Healthcare Science and Allergy
Research, the Swedish Nutrition Foundation, Research Foundation of Bertil
Eriksson, Fund of Uppsala Hemsysterskola, JC Kempes Memorial Fund,
Patentmedelsfonden för odontologisk profylaxforskning, the Swedish
Institute, COST Action-99, Knut and Alice Wallenberg’s fund, NEON and
Foundation of Engelbrekts Barnavårds & Husmodersskola.
Umeå, 2001
……………………………
71
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