Download NEWER TRENDS IN HUMAN NUTRITIONAL REQUIREMENTS

NEWER TRENDS IN HUMAN NUTRIENT REQUIREMENTS
DIETARY STANDARDS AND BALANCED DIETS
B. S. Narasinga Rao
Former Director, National Institute of Nutrition, Hyderabad
Introduction
Human nutrient requirement was defined by the League of Nations in 1935 1.
Attention was paid initially to the major nutrients, and some micronutrients, the
deficiencies of which were encountered among poor population groups in
different parts of the world and some data on human requirements were also
available. Subsequently, in forties National Nutrition Organizations of different
countries recommended desirable intakes of these nutrients by their population
on their habitual diets.
The Nutrition Advisory Committee (NAC) of the Indian Research Fund
Association (IRFA), now Indian Council of Medical Research (ICMR),
recommended Dietary Allowances (RDA) of these nutrients for normal Indians 2.
This Committee also recommended balanced diets corresponding to Indian
habitual diets to meet the RDA of nutrients.
The RDA in different countries is being revised periodically (once in 10 years) as
fresh information on human nutrient requirements accumulated.
The International organizations like FAO, WHO (now also UNU) took up the task
of defining the human nutrient requirements through consultation of Expert
Groups periodically since 1950, so that their proposals would be useful
internationally. These organizations have also been revising requirement of
nutrients periodically. The latest FAO/WHO/UNU recommendation on human
requirements of nutrients and their application was done during 2000-2005.
RDA for Indians has also been revised by the ICMR after 1944 2 through its
Expert Committees in 19583, in 19684, in 19785 and in 19906 the latest revision is
now being undertaken.
Impact of Nutrients on Non-Communicable Diseases (NCD)
During the past couple of decades there have been several changes in the socioeconomic conditions of Indian population, and linkages between nutrients and
non communicable diseases (NCD) like diabetes, cardiovascular diseases
(CVD), cancer etc. have been recognized7 This holds good in case of certain
nutrients which in their metabolic behavior and biochemical functions in fulfilling
their nutritional function offer protection against NCD, which needs to be
highlighted. Recently newer methodologies and more rational approaches have
been developed in case of certain nutrients like, energy, protein, fat, calcium, and
some micronutrients like vitamin C, iron, zinc Newer information has become
11
available in case of certain nutrients like selenium, biotin and pantothenic acid
and pyridoxine and fat soluble vitamins like vitamin E ( TE) and vitamin K. Fresh
data on carotene conversion to retinol which is essential in meeting vitamin A
requirements in terms of provitamin A like -carotene and other carotenes from
horticultural source.
Figure: 1
New Life Styles
Mostly In
Urban Area
Consumption Of
Rich Food With High
Fat Content →High
Energy Intake
Sedentary
Activity
Occupation
Over-Weight
BMI> 25.0
I shall discuss some of
the
newer
developments
on
human requirements of
some of the nutrients,
newer methodologies
that are more rational,
and
interrelationship
between
nutrient
intakes in terms of
prevention of NCD.
Energy Need For
Revising
Requirement
There
have
been
changes in life styles of
our
population,
particularly the urban
population. This has
lead to a tendency
Chronic
towards
more
Diseases:
sedentary life styles
CHD, Diabetes,
with an increase in
Cancer Etc.
intake
of
diets
expensive and rich in fat component. This has led to an increase in energy intake
leading to overweight and obesity among adult as well as children and
adolescents which as we know lead to increased tendency to chronic diseases
such as heart disease and metabolic disorders like diabetes (Figure 1).
Obesity
BMI > 30
This tendency is not as much among the rural population, but it is on the increase
(Figure 1). The rural population is more active with increased moderate and
heavy activity life styles. A recent NNMB survey (1996-97) of a rural population
(Table 2) indicates, that males are mostly (66%) moderately active, 33%
sedentary and very small percentage (1.2%) are engaged in heavy activity. Most
of the females (63%) are sedentary, 37% are moderately active and negligible
number (0.3%) are engaged in heavy activity.
12
TABLE 2: Activity status of Men and Women in a Rural area in India
Men
Women
Activity
status
No
%
No
%
Sedentary
1349
33.3
2765
62.7
Moderate
2650
65.5
1632
37.0
Heavy
48
1.2
14
0.3
Pooled
4047
100
4411
100.0
Source: NNMB: Report of the second repeat survey 1996-97.
Total
No
4114
4282
62
8458
%
48.6
50.6
0.8
100.0
Earlier, energy expenditure of adults was measured on the basis of energy cost
of different activities and time spent in each type of activity. While energy cost of
various activities could be measured accurately, the time spent in each type of
activity, accurately, particularly, during moderate or heavy activity is a difficult
task. Therefore there was certain amount of uncertainty in assessing the energy
expenditure during moderate and heavy activity.
And also the energy
requirement of children (1-10 yrs) was assessed on the basis of energy intake of
healthy normally growing children.
There have been newer developments during the last two decades in measuring
energy requirement of humans more directly and perhaps more accurately. It is
through the doubly labeled water i.e. 2H2 O18 turnover of which is measured by
estimating the excretion of the label in the urine over 10-20 days after
administering the labeled water8 Since doubly labeled water (DLW) is very
expensive, this methodology is rather expensive. Still this method has been used
all over world in different countries among nearly 500 children. It has been used
among adult also to confirm the results of the conventional method.
TABLE 3: Energy Requirement of Children (1 – 10 Yr) Recommended by FAO/WHO/UNU (2004),
New Values as compared to old values (ICMR 1989)
Boys
Girls
Old
New
∆
Old
New
∆
%
%
Age Years Values Values difference
values values difference
difference
Difference
Kcal/d Kcal/d
Kcal/d
Kcal/d Kcal/d
kcal/d
1–2
1096
948
-148
-13.5
1078
865
-213
-19.8
2–3
1301
1129
-172
-13.2
1190
1047
-143
-12.0
3–4
1493
1252
-241
-16.1
1310
1156
-154
-11.8
4–5
1531
1360
-171
-11.2
1458
1241
-217
-14.9
5–6
1778
1467
-311
-17.5
1643
1330
-313
-19.1
Preschool
Age Mean
1440
1231
-209
-14.5
1336
1129
-207
-15.5
6–7
7–8
8–9
9 – 10
1948
2030
2034
2160
1573
1692
1726
1865
-375
-338
-308
-295
-19.3
-16.7
-15.1
-13.7
1750
1858
1792
1848
1428
1554
1595
1678
-322
-304
-197
-190
DLW method used among young children (1-10 yr) has yielded lower values
(Table 3) than those reported earlier (1989). There is therefore a need to revise
the daily energy requirement of this group.
13
-18.4
-16.4
-11.0
-10.3
In keeping with the current trend towards sedentary life styles with minimal nonoccupational physical activity, the daily energy expenditure may be as low as
2128 Kcal for a 60 Kg adult man and 1638 Kcal for an adult woman, with energy
requirement coming down as the body weight decreases (vide Table 4).
TABLE 4: Energy Requirement of adults of different body weights at two levels of
sedentary daily activity
MALE
FEMALE
Body
Body
PAL
PAL
Weight
BMR
Weight
BMR
Kg.
1.53
1.4
1.53
1.4
Kg.
45
1298
1986
1817
40
1031
1577
1443
50
1370
2096
1918
45
1101
1685
1541
55
1443
2208
2020
50
1171
1792
1639
60
1515
2318
2121
55
1241
1899
1737
65
1588
2430
2223
60
1311
2006
1835
70
1660
2540
2324
65
1318
2113
1933
Daily sedentary activity at a normal (PAL1.53) and reduced level (PAL 1.4) of activity.
The revised energy requirement of adults with different body weight engaged in
sedentary and moderate activity is given in Table 4. If this energy intake is
maintained according to the current body weight and excess energy intake is
avoided, the risk of over-weight, obesity and chronic diseases may be avoided.
Dietary guidelines to maintain the intake of energy and other nutrient have to be
formulated.
TABLE 5: Energy intake of preschool children (Kcal/d) of Different Socio-economic
Classes and their Adequacy Compared to Modified Requirement (2004)
a
b
c
Energy Intake
As percent of 1989 As percent of New
Socio economic class
Kcal/d
RDA
values
Urban well to do
1438
104
122
Rural poor
777
56
66
Urban low income
852
61
72
a
b
NNMB Survey; Nutrient Requirements and Recommended Dietary Allowances for Indians
c
1989, ICMR; New Values: adapted from FAO/WHO/UNU Report on Human Energy
Requirements 2004 (vide Table 3)
Current intake of energy by pre-school child of different socio-economic group
are given in Table 5 as compared to the earlier ICMR (1990) 6 and the current
FAO/WHO/UNU (2004)9 values. We may accordingly have to reassess the extent
of energy deficiency among our poor preschool children.
Protein Requirements
Earlier, protein requirement used to be assessed in terms of N requirement
based on minimal N balance or minimal N loss through urine and sweat on a N
free diet. Protein requirement (N x 6.25) was assessed on the basis of minimal N
loss and absorption of dietary protein.
14
The FAO/WHO/UNU consultative group revised human protein requirement in
200210. Instead of determining protein requirement in terms of N needs, this
group estimated human protein requirements in terms of total amino acid
requirement reassessed recently which are much higher (2-3 times) than the
earlier values (Table 6). This International group reassessed human protein
requirement in terms of latest amino acid requirement values i.e. the amount of
dietary protein to be daily consumed to provide the recommended daily amount
of amino acids. The recommended figure in terms of egg or animal protein is 0-6
mg/kg. In terms of vegetable proteins which have a lower
TABLE 6: Revised indispensable amino acids requirement (2003) compared to earlier
estimate (1985)
FAO/WHO/UNU 1985
FAO/WHO/UNU 2003
Amino Acids
mg/kg/d
mg/g protein
mg/kg/d
mg/g protein
Histidine
8-12
16
10
15
Isoleucine
10
13
20
30
Leucine
14
19
39
59
Lysine
12
16
30
45
methionine
10.4
16
Cystine
13
17
4.1
22
Meth + cystine
14
19
15
38
Theonine
7
9
20
23
Tryptophane
3.5
5.0
4
6
Valine
10
13
26
39
Total IIA
84
127
111
271
x
-1
-1
Total Protein
0.60g/kg /d-1
0.66g/kg /d-1
Safe level of
-1
-1
0.75g/ kg /d-1
0.83g/kg /d-1
protein M+ 2SD
“X’ High quality protein like egg, milk etc
Requirement in terms of dietary proteins: safe level adjusted to provide the above quantities of protein x digestibility’
Indian adult requirement on the basis of amino acid content and digestibility of 84%
PD<CA= 99.3 x 85.4
------------ = 84.4
100
2002 FAO/WHO/UNU values of 0.66 kg-1/d-1 = 0.7899/ kg-1/d-1 and this would work out in terms of safe levels of
protein (M + 2SD) would be 0.98 g kg-1/d-1 or nearly 1g/kg a value recommended by the ICMR, 1989 expert group for
a normal man of 60kg and woman of 50 g per day.
digestibility and content of the essential amino acids, a higher level of vegetable
protein needs to be consumed to meet the daily amino acid requirement. These
are shown in Table 7 in terms of dietary protein predominantly of vegetable
source a combination of cereal + legume + milk consumed in India. The required
amount of proteins in this mixture in terms of amino acid can also be fulfilled at
various ages. Since the nutritive values of these proteins are lower than egg, a
higher level of this protein combination has to be consumed to meet the daily
protein need.
Protein requirement of children, adolescents, pregnant and lactating women were
also derived using the same principle of amino acid scores for maintenance
except for providing for tissue deposition under these conditions. The present
ICMR expert group will also be arriving at the protein requirement of adults,
children, pregnant and lactating women in terms of cereal + legume + milk
15
TABLE 7: Protein requirement of different age groups as assessed by amino acid
scoring method in 2003
Protein
Protein
Group
Group
Requirement g/d
Requirement g/d
16-18 Years
Pre School Children
Boys
60.2
1-3 years
15.6 Girls
58.4
4-6 years
20.0 Adults
School Children
Man
60
7-9 years
28.7 Woman
50
10-12 years
39.3 Pregnant woman
72.6 (50 + 22.6)
Adolescents
Lactating women
13-15 Yrs. Boys
51.9 0-6 m
66.5 (50+16.5)
Girls
52.2 6-12m
61.0 (50+11))
The Recommendation is in terms of Indian Dietary Protein composed of cereal + legume + milk
proteins, in the ratio of 8:2.4:1
proteins (8:2.4:1) combination which corresponds to protein from a balanced
Indian diet. These values are also given in Table 6.
Other Macro-Nutrients-Fat and Calcium
Fats
Fat in the diet is an important source of energy besides carbohydrates and
proteins. It is a concentrated source of energy providing 9 Kcal per g. A certain
level of fat in the diet is essential to meet the energy requirement of young
children. On a cereal-based diet, Fat, besides serving as a source of energy and
essential fatty acids (EFA) to meet the body’s metabolic requirement facilitates
absorption of fat-soluble vitamins. There are two sorts of EFAs, one is derived
from (w-6) n-6 fatty acids with two unsaturated bonds essential for the synthesis
of cell membranes and the other is derived from n-3 fatty acids (w-3) which are
recognized only in recent years as essential for certain metabolic functions and
for protecting against certain heart diseases. Fish oil is an important source of
long chain w-3 fatty acids. Certain vegetable oils like Soya, linseed and canola
are also rich in linolenic acid of normal chain length, which gets converted into
long chain w-3 fatty acid in the body.
Besides emphasizing the metabolic importance of EFA of both n-3 and n-6 type
and their hypocholesterolemic and cardiacdiseases protecting properties, there is
a need to limit saturated fatty acids as well as total dietary fat since both are
hyper cholesterolemic and pro-heart diseases. The total fat content in a diet
should not exceed 30 per cent of calories. In the context of fat intake and heart
diseases, mono-unsaturated fatty acids (MuFA) in a dietary fat known to also (viz
Olive oil) play a role in protecting against proneness to heart diseases.
In view of increasing tendency to sedentary Life Styles associated with a higher
intake of energy leading to overweight, obesity and associated ill-health,
individuals should keep the fat intake at a minimum for meeting its minimal
16
TABLE 8: Recommended intake of fat by Indians Expressed as % of energy
Fat/Fatty
Adolescent
Adolescent
n6/n
Adult
Pregnant
Lactating
Acid
13-15
16-18
3
Total fat %
25
30
25
25
30 5-10
Invisible fat
10
10
10
12.5
12.5
“
Visible fat
15
20
15
12.5
17.5
“
SFA %
8-10
8-10
8-10
8-10
8-10
“
MUFA %
10-12
8-10
8-10
10-12
10-12
“
PUFA %
8-10
8-10
8-10
8-10
8-10
“
n-6%
6-8
9.0
11
4.5
6
“
n-3%
1-2
1.4
1.8
1-2
2-3
“
The Recommended fat intakes are based on suggestion made by WHO-NIN workshop 2005.
functions and with adequate n-6 and n-3 fatty acids which will also help in
keeping down the daily energy intake.
Recommended daily fat intake for different ages of Indians is given in Table 8.
Minerals:calcium
Calcium is an essential mineral for bone formation, deficiency of which leads to
reduced bone formation, osteoporosis and bone fracture with an overall
restriction in bone formation (bone size) and growth.
The strange observation is that bone fractures are more frequent among
communities (west) who consume a higher level of calcium (~ 1g a day) since
their intake of milk is quite high as compared to populations in the developing
countries, who consume lower levels of calcium (~500 mg a day) and have lower
fracture rates. Nordein11 has presented evidence resolving this paradox.
According to him, this dramatic difference is due to difference in intake animal
protein and sodium, lower intake of both of which limit the loss of calcium in
urine reducing the calcium requirement.
High dietary calcium intake observed in developing counties i.e. in the range of 1
– 1.5 g a day is not possible without a high milk intake. Therefore, calcium intake
in the developing countries lies in the range of 300 mg – 600 mg a day, derived
mainly from cereals and vegetables, especially green leafy vegetable. Some
millets like Ragi
(Eleusine coracana) and pseudocereals like rajakeera
(amaranthus) are rich sources of calcium. There is evidence that body can adapt
to different calcium intake, thus calcium balance has been observed on both high
level (developed countries) as well as on low levels of calcium (developing
countries). Calcium requirements can be assessed by
 calcium balance on different calcium intake,
 factorial model: Ca accretion as bone mineral determined, isotopically or by
scanning
 clinical trials on response to changes in bone mineral content/density on
different levels of calcium intake.
17
Short-term balance studies will not yield fruitful results and only long-term
balanced studies of months duration can yield consistent results 12, Assessment
of Ca requirement should be based on results obtained in normal subjects rather
than in clinical subjects with depleted bone calcium.
It is felt that the earlier estimates of calcium requirement (1978, 88) of Indians are
lower. This was perhaps influenced by the concept of not being able to provide
higher levels of dietary Ca to our poorer population. There has been some
evidence accumulated based on bone density measurements 13 that the earlier
RDA is rather low and needs to be increased. There has been widespread
occurrence of low bone density and osteoporosis among Indian women of low
income, especially among those subjected to the stress of pregnancy and
lactation without supplementary calcium intake. Therefore, after examining the
evidence on calcium status of Indian population, which has been studied in
recent years, the earlier recommendation has been revised upward and the
revised values of Ca RDA for Indians are given in Table 9. However, it is
suggested that more systematic studies are undertaken on calcium requirements
of Indian population employing isotopic or more recently developed methods.
TABLE 9: Revised Recommended intakes of calcium and phosphorous (mg/d) compared
to 1988 values
New Values RDA
Old Values RDA (1988)
Group
Ca
P
Ca
P
Adults
Men
600
400-600
400
400
Women
600
400-600
400
400
Pregnancy
&
1200
1000-1200
1000
1000
Lactation
Infants
500
750
500
750
Children
1-9 yrs
600
400-600
400
400
10-15 yrs
600-800
600-800
600
600
16-18 yrs
600
500-600
500
500
Calcium/phosphorus ratio is kept at 1.0 for all groups except for infants where it is kept at 1.5.
Micronutrient Requirements
There is a wide range of micronutrients both vitamins and trace elements
including iron, zinc and selenium. All of them have been studied systematically
concerning their essentiality and their human requirements. There are some
observations made during these studies, which need to be highlighted in the
context of their requirement for Indians. These include minerals like iron and zinc,
and vitamins like vitamin A and other provitamin A i.e. ß and other carotenes,
folic acid and vitamin B-12. I would like to highlight these points and other latest
development to concerning their human requirements especially with reference
to Indians.
Iron
Iron is an important mineral whose deficiency is widespread in developing
countries and even in developed countries among women leading to iron
18
deficiency anaemia (IDA). Iron requirement and factors affecting the absorption
of iron from diets based on plant foods are emphasized in the context of fulfilling
iron requirement and preventing iron deficiency anemia among India.
Iron deficiency anaemia is widespread which arises more out of poor iron
absorption from diets based on plant foods than the iron content of these diets.
Iron intake and contamination Iron
Food component of diet, particularly the grains, are estimated as purchased and
iron content of diet based on these grains gets overestimated, to the extent of 2036 % due to contamination iron (Table 10). This contamination iron is not
absorbed. Iron absorption determined on diets containing contaminant iron, using
extrinsic tag technique, has been shown to range from 2.6 – 3.614, with an
average of 3.0 %. However, if iron absorption is determined on similar diets free
from contamination iron, the absorption may be around 5.0 %. Many plant food
based diets without contaminant iron may meet iron requirement of an adult man
even with 5 % absorption on an intake of 20 mg iron.
TABLE 10: Contaminant iron in diets consumed in Different Regions of India
Iron content
Percent
True iron content
Region
mg/day
contamination
mg/day
Andhra Pradesh
29
30
20.3
Maharashtra
48
26
34.0
West Bengal
31
29
22.0
Uttar Pradesh
45
36
28.8
Gujarat
41
20
29.1
Karnataka
57
Mean
41.5
29
29.5
It is recommended that iron content is determined from plant foods free from
contamination iron.
a
TABLE 11: Dietary Iron absorption from Habitual Indian Diets in Different physiological
groups
Mean Iron Absorption (%) from
Groups
Rice based Diet
Mixed Cereal based diet
Wheat/millet based diet
Adult Males
5.0
3.0
2.0
Adult Females
8.0
5.0
3.3
Children
5.0
3.0
2.0
Adolescent males
5.0
3.0
2.0
Adolescent
females (10-18
8.3
5.0
3.3
yrs)
Post Menopause
5.0
3.0
2.0
Females
Pregnancy
13.3
8.0
5.3
Anaemic males
10.0
6.0
4.0
Anaemic females
16.7
10.0
6.7
a
Determined by extrinsic tag technique.
19
Iron absorption from habitual diets in different physiological groups determined
by extrinsic tag technique is given in Table 11.
Methods to improve iron from vegetarian diets:
The second point which needs to be emphasized in the context of meeting iron
requirement on plant food based diets is to consider the possibility of improving
the iron absorption on such diets.
It has been suggested by Hallberg15 based on his African studies, that inclusion
of 100 mg ascorbic acid in diets based on plant foods would improve absorption
of iron significantly. This level of ascorbic acid consumed with the diet would
meet the basic metabolic function of the Vitamin besides improving iron
absorption to a reasonable extent. Hence, it is suggested that a similar level of
ascorbic acid may be included in Indian diets to improve iron absorption. It is
suggested that some more studies are done on Indian diets to show whether a
significant improvement in iron absorption is also achieved from Indian diets by
including 100 mg ascorbic acid in the diet or whether a higher level of ascorbic
acid is required on Indian diets.
One of the reasons for poor iron absorption from Indian diets is they are rich in
polyphenols, tannins etc. An attempt also should be made to reduce dietary
component rich in these inhibitors viz. tamarind (rich in tannins) may play an
important role in inhibiting iron absorption. We have shown that iron absorption
on a typical south Indian meal cooked without tamarind is much higher i.e. 10 %
than on a meal cooked with tamarind that is 3 % (unpublished – Rao BSN and,
Prabhavati, T.N).
TABLE 12: Proposed RDA for Iron in Indians with Revised absorption values
Dietary iron RDA (mg/d)
Requirement
Group
Current
Suggested “x”
mg/d
RDA
RDA
Adult man
0.84
28
20
Adult Women
1.54
30
21
Pregnant women
3.00
37.5
37.5
Lactating woman
1.50
30.0
21
Children : 1-3 years
0.35
11.50
6.4
4-6 years
0.551
18.40
10.2
7-9 years
0.78
26.0
13.2
Adolescents
Boys: 10-12 years
1.02
34.20
16.1
13-15 years
1.243
41.40
27.2
16-18 years
1.485
49.5
28.2
Girls: 10-12 years
0.945
18.9
18.5
13-15 years
1.401
28.0
27.0
16-18 years
1.497
29.9
26.6
“x’ Indian diets contain ~ 7mg/1000 kcal (calculated on the basis of revised values for iron
from Nutritive value of Indian Foods); “x’ absorption of iron in this diet is around 5% in Males
and 8% in women.
20
Currently proposed iron requirement of different physiological groups are given
on diets free from contaminated iron (Table 12) in comparison with earlier (1989)
figures.
Relationship between iron deficiency and other nutrient deficiencies:
There is another interesting feature of anaemia due to iron deficiency. Among
communities in India who suffer from iron deficiency anaemia, there are other
nutrient deficiencies of energy and other micronutrients like vitamins. It is
observed that anaemia cannot be fully corrected and Hb level brought back to
the normal level with iron treatment alone. Apart from haemopoetic nutrients like
folate and vitamin B-12, anaemic subjects have to be supplemented with other
nutrients like Vitamin A, riboflavin, B-6 and energy, to correct their deficiencies, to
cure anaemia fully and to normalize Hb levels16. There appears to be a need for
correcting the coexisting other micro nutrient deficiencies also besides treatment
with iron in correcting IDA fully. The mechanism of interaction between iron and
other micronutrients indicated above in causing IDA is not known. The reported
interaction between anaemia and other micronutrient deficiencies, which coexist
among our poor communities, need to be studied further.
Zinc
Zinc is an essential trace element being a component of large number of
enzymes. Zinc deficiency, unlike other trace elements, has been reported
among different population groups of the world17, 18. Although much work has not
been done on Zn deficiency and its health consequences in India, it is believed
that zinc deficiency may prevail among children of poor income groups
contributing to their poor growth19
Zinc content of Indian food and diets20 have been determined Zinc balance on a
typical Indian diet has been determined particularly at NIN21 besides other trace
elements. Based on zinc intake and absorption, zinc requirement has been
estimated. During this study contamination of diets and excretion was avoided
and zinc was estimated by AAS. Zinc balance was determined at different levels
of intakes of dietary zinc (4 - 12 mg). There was a correlation between intake (x)
and balance (y) Y = 2.51 + 0.35 x. From this equation, the minimal zinc intake
for equilibrium was found to be 7.7 mg/day with a mean absorption of 34.5 %
with endogenous fecal loss of 1.7 mg zinc.
Taking into account the reported sweat loss of zinc of 1.26 mg daily intake of zinc
should be 10.8 mg or 11 mg with absorption of 35 %.
Zinc deficiency if any may be masked by other nutrient deficiencies, which
dominate among our poor population groups. There is a need for systematic
studies on deficiencies (particularly immunological deficiencies) specifically
attributed to zinc deficiency and reversible with zinc supplementation. It is also be
21
possible that other deficiencies may mask manifestations of zinc deficiency and
correction of other deficiencies may throw up zinc deficiency symptoms. There is
a need for more systematic research in the area of zinc deficiency and zinc
nutrition among our population.
Selenium
Selenium is a trace element essential for man, which has drawn attention of
nutritionists only in recent years. It is an antioxidant, which has been shown to
offer protection against oxidation and free radicals in cells. It acts as
selanoprotein in different forms in the body; fifteen selenoproteins recently have
been identified.
As an antioxidant, it has also been shown to offer protection against cancer.
Studies on selenium nutrition and its function are limited and hardly any work is
reported from India. Before taking up studies on nutritional aspects of selenium,
there is a need to study the selenium content of commonly consumed foods.
Dietary content of selenium and its absorption from Indian diets needs to be
determined. Its metabolism, absorption, blood levels, excretion all have to be
determined among Indian subjects of different ages and physiological groups and
socio-economic conditions. Any systematic study on selenium nutrition is
possible only when the above basic data are collected.
Vitamins
A considerable amount of research on chemical, biochemical, physiological and
nutritional aspects of vitamins have been carried out in India since 1918. These
TABLE 13: Vitamins essential for man, deficiency encountered and research done on
their requirement
Deficiency
Requirement
Vitamins
Food content
encounted
studies
Available as
Fat soluble:
Keratomalacia
Yes
provitamin,
Vitamin A
carotene
Vitamin D
Vitamin E
No Def
No
Nil
Vitamin K
No def
No
Nil
Water soluble:
Beri Beri
Yes
Yes
Thiamine
Riboflavin
Angular stomatitis
Yes
Yes
Niacin
Pellagra
Yes
Vitamin B6
?
Yes
Pantothemic acid
No
?
No
Biotin
No
Megaloblastic
Folic acid
Yes
Yes
Anaemia
Megaloblastic
Vitamin B12
?
Yes
Anaemia
Vitamin C
Scurvy
Yes
Yes
22
studies cover both fat-soluble and water soluble vitamins. Studies on the human
requirement of the vitamins have also been carried out since deficiency of
several of these vitamins was encountered among our population. A list of
vitamins covered by Indian research is given in Table 13. Hitherto no attention
was drawn to some fat-soluble and some water-soluble vitamins as no deficiency
of these vitamins was encountered among Indian population. There have also
been no systematic studies on the content of these new vitamins in Indian foods
and also their intake by population groups.
I am not going to discuss about these vitamins whose requirement has already
established, but discuss certain uncertainties, which persist, and newer facts,
which have emerged with regard to meeting the requirement of certain vitamins
like vitamin A vitamin C folic acid and vitamin B-12.
Vitamin A and provitamin A
Although retinol is the chemical form of vitamin A, it is the provitamin A, betacarotene and some other carotenes, which largely fulfill this function of meeting
the vitamin A requirement in developing countries like India. In this context the
question of conversion of beta-carotene from plant sources, to retinol and its
absorption still remains largely unresolved
TABLE 14: Reported carotene: Retinol conversion ratio for recommending carotene
intake to meet Vit.A requirement.
Recommend
Observed
Age
carotene intake
Investigator
Source
carotene
group
to meet retinol
retinol ratio
requirement
WHO (1967) FAO (1985)
Adult
Carrot
6:1
3600
Wilson et al (1937)
ICMR (1978,1988) Rao & Rao
(1970) Lal. Reddy (1970)
Adult
Children
FAO/WHO (2002)
Adults
Furr H.C. (1989)
Adults
Haskell M.J. (1998)
Adults
Sivakumar B.(ICMR (2008)
Adults
GLV
Amaranthus
-carotene
sources
-carotene
sources
-carotene
sources
-carotene
sources
4:1
2400
6:1
2600
16:1
?
22:1
?
8:1
4800
The conversion of plant -carotene to retinol in human intestine is very important
in defining Vitamin A requirement in terms of -carotene i.e. provitamin A.
FAO/WHO when it recommended vitamin A in terms of -carotene assumed a carotene retinol conversion ratio of 6:123 based on observations of Wilson et
al24.on absorption of carotene from carrot in human subjects. The Expert Group
of the ICMR based on the observation of -carotene absorption from
amaranthus, a green leafy vegetable (GLV) at NIN6 recommended a conversion
ratio of 4:1. In the light of recommendation of horticultural approach to combat
23
vitamin A deficiency, there have been a number of community studies 25 in
Indonesia, which have reported the ineffectiveness of plant carotenes as a
source of retinol. This has lead to restudy26, 27 of conversion of carotene from
plant sources to retinol. These and earlier reported figures for conversion of carotene to retinol are given in Table 14. If these high figures are true, it may not
be possible to meet vitamin A requirement through plant carotene source at all.
A critical reevaluation by Shivakumar at NIN28 of studies which reported high
conversion factors and on the basis of more recent studies on carotene
absorption, blood levels of retinol following carotene feeding to human
volunteers, a more reasonable carotene retinol conversion factor of 8:1 has been
recommended. The current ICMR Expert Group may also may recommend this
figure. The consultative group of FAO/WHO/UNU, which revised human
requirement of vitamins, recently29 has agreed to retain the earlier conversion
factor of 6:1 till the ongoing studies suggesting a higher conversion factor are
proven.
The retinol equivalent of carotene will depend upon the absorption of carotene
from foods, which will again depend upon the type of carotene and the food
source of carotene. Absorption appears to be much better with GLV than green
or yellow vegetables. Absorption may be better if green leaves and vegetables
are cooked and facilitated in presence of fat in the diet. Some amount of fat is
essential in the diet to promote absorption of fat-soluble vitamins like -carotene.
There is a need to promote further research on meeting the human vitamin A
requirement from GLV and other yellow or green vegetables. Community studies
need to be carried out to confirm the applicability of horticultural approach to
prevent vitamin A deficiency. In this context, the composition of the diet like the
amount of fat, the sources of carotene, whether the vegetables are cooked or not
may all be important.
Vitamin C
Many metabolic studies have shown that human requirement of ascorbic acid is
only around 20 mg/d. Ascorbic acid has other activities as an antioxidant along
with vitamin E and selenium. It is also known to promote iron absorption from
plant foods (vide section on iron)
Therefore, it is suggested that diets deriving iron from plant source should
contain at least 100 mg ascorbic acid to promote dietary iron absorption and this
amount may also promote antioxidant function. The amount of ascorbic acid to
be present in the diet to promote iron absorption may depend upon the type of
diet i.e. quantity of inhibitors of iron absorption like phytate, it may contain tannins
and other polyphenols. This has to be determined for each type of traditional diet
(vide section on iron). In defining vitamin C requirement, its activity in promoting
24
iron absorption to meet iron requirement may have to be included as one of its
function.
Folate
Folate function and its status have been reassessed in recent years. Folate plays
an important role in single carbon metabolism. Haematological status is also an
indicator of folate status, besides plasma folate level being more than 15µg per
100 ml. The biomarker, plasma homocystein is a very sensitive indicator of folate
status and can be used as an indicator of folate adequacy. Homocystein is also a
risk factor in cardiovascular disease. There is now conclusive evidence that most
neurotube defects (NTD) can be prevented by ingestion of folate.
TABLE 15: Suggested daily intake of folate by different groups
„a‟
b‟
Old values
Revised „
Group
1988
RNI for folate
µg/d
µg/d
Adult man and woman
100
400
Pregnant woman
400
600
Lactating woman
150
500
Infants 0-6 months
80
6-12 months
25
80
Preschool children: 1-3 years
40
160
4-6 years
50
200
School children: 7-9 years
60
10-12 years
70
300
Adolescents: 13-15 years
100
16-18 years
100
400
a
in terms of free folate
b
in terms of total folate in foods
b
FAO/WHO
UNU 2002 µg/d
400
600
500
80
80
160
200
300
400
400
On the basis of current studies, there is evidence that folate in foods is not very
stable and food folate bioavailability may range from 25–50 %. On the basis of
these pieces of evidences, FAO/WHOUNU Consultative Group has recently
recommended a new set of values for folate requirement 29 and RNI (vide Table
15). It is 400µg for an adult 600µg during pregnancy and 500µg during lactation
and it varies from 80µg for the infant to 400µg for adolescents.
ICMR Expert Group in 1989 recommended RDI for folate in terms of free folate in
view of uncertainities of intestinal absorption of polyglutamates and on the basis
of normal requirement of 75µg in Indian subjects, 180µg of free folate for an adult
was recommended. A higher level is needed during pregnancy and lactation.
Since it is difficult to provide free folate from foods only, provision of medicinal
folate during these periods was recommended. For other age groups for infants
and children, daily intake of free folate 25µg to 100µg was recommended (Table
15).
Since all Indian foods contain both free and total folate 30, it is suggested that
folate intake may be recommended in terms of total folate assuming about 50 %
25
absorption of food folate. Suggested figures are given in Table 15, it varies from
80µg for infant to 500µg for a pregnant woman.
Vitamin B12
As a component of several coenzymes, Vitamin B12 has an important role in the
synthesis of nucleic acids. Its metabolism is closely interrelated with that of folic
acid. Deficiencies of Vitamin B12 lead to abnormal haemopiosis resulting in
megalloblastic anaemia as in the case of folic acid deficiency. In addition, vitamin
B12 deficiency may result in neurological manifestations due to subacute
combined degeneration of the spinal cord although rare in India.
Vitamin B12 is present only in foods of animal origin like liver, meat, fish, eggs and
milk. Bacteria can synthesize vitamin B12 and when vitamin B12 is present in
foods of vegetable origin, it is also an indication of bacterial contamination,
microflora present in human large intestine can synthesize vitamin B 12 and
whether man absorbs it is not proven. However, bacterial contamination of foods
and water can contribute small quantities of vitamin B12. Since, liver can store
enough Vitamin B12; it is rather difficult to establish vitamin B12 requirement in
humans.
Depending upon the method employed, the daily requirement of the vitamin has
been shown to be as low as 0.1µg to as high as 1.0µg. Diet survey data
collected by NNMB24 indicate that B12 intake is as low as 0.7µg when only small
amount of flesh foods, eggs or milk products are included in the diet. Very large
segments of our population do not consume any significant vitamin B12 through
diet since their diets can contain hardly any animal foods.
Due to limited access to vitamin B12 in Indian diets, RDI of vitamin B12 has been
placed at a moderate level of 1-0µg per day for an adult by the 1990 ICMR
Expert Group19. It is suggested that foetus in pregnancy need 0.3µg B 12 and the
quantity excreted in breast milk is about 0.3µg. On the basis of this evidence
additional requirement of 0.5µg / day is recommended during pregnancy and
lactation. In infants and children, also RDI has been placed at 0.5µg/day.
In view of limited resources of Vitamin B12 in Indian diets and in absence of any
widespread Vitamin B12 deficiency among Indian population, the above RDI
appears reasonable. However, FAO/WHO/UNU Consultative Group which
recently re-examined Vitamin B12 requirement of humans10 has recommended
2µg Vitamin B12 in adults. This conclusion is based on in intramuscular vitamin
B12 needed to prevent remission of pernicious anaemia. Therapeutic response
cannot be the basis of RDI. This level of intake may be suitable for people
whose traditional diets are rich in animal foods as in the western countries but
not in countries like India.
26
There is in fact some future research needed in India on establishing the
requirement of Vitamin B12 among Indian population whose dietary source of
Vitamin B12 is extremely limited. There is also need to carry out research to
improve the resources of B12 in India with the help of probiotics. From
lactobacteria to produce milk based ferment products like yoghurt, curd which are
widely consumed in India.
Balanced Diets
In the end, I would like to describe an improved balanced diet based on Indian
traditional foods and meals incorporating some of the newly proposed ideas on
recommended dietary intakes of nutrients and non-nutrient health protecting
agents against chronic diseases, which are increasing with the current life-styles.
There is a need to restrict the intake of energy and fats, particularly by those with
sedentary life styles to avoid overweight and obesity.
A typical balanced diet (low cost) and its nutrient content are given in Table 16.
The energy content is kept at 2100 Kcal (for an adult man of 60 kg), total fat 19
% of energy, 13.5 % of it being visible and 8 % fat being non-visible fat, the fatty
acid intake being both w-6 and w-3, the ratio of the two is kept at 5:1. The visible
fat or oil has mono-unsaturated, linoleic acid (w-6) and linolenic (w-3) fatty acids,
in the ratio of 10:6:1
TABLE 16: A typical balanced diet for a sedentary man (60 Kg.) and its nutrient content
„x‟
Food Stuffs
Quantity g/d
Nutrients
Intake per day
Cereals (mixed)
350
Energy (Kcal)
2100
Rice + Wheat
Pulses
60
Protein (g)
60
(Red gram dhal)
Leafy vegetables
50
Calcium (mg)
628
(Amaranthus)
Other vegetables
60
Iron (mg)
15.4
(French beans)
Vitamin A
Roots + Tubers
22634
(pro vitamin A
50
(potato)
(18330)
carotene)
Fruits (mango)
100
Riboflavin (mg)
141
Milk (cows)
200
Thiamine (mg)
1.52
Oils & Fats
Vitamin C (mg)
30
134
(Safflower + Canola)
(Ascorbic acid)
Sugar/jaggery
30
Niacin (mg)
15
One egg
Non Vegetarian
Folic acid/ g
Or
96.3
Substitute 50% of pulses
Free
30g meat
286.2
Total
Substitute 100% of
2 eggs or 50 g
0.3 (veg diet)
pulses
Vitamin B12
meat
1 or >1 (non Veg)
“x’
contains adequate vit B6, pantothenic acid, biotin, vit E and Vit K, selenium antioxidants,
Sod. 3891 g and potassium (g) 2663 and K/Na ratio 6.84, Mg: 920 mg. total fat 44g (19.0
en%)visible 30g (13.1 en%) invisible 14g (6.0 en%)
27
The diet provides adequate other B vitamins like pyridoxine, pantothenic acid and
biotin and fat soluble vitamins like vitamin E and vitamin K. It has enough
selenium (~ 50 µg) magnesium (920 mg). Dietary fiber (50 g) and enough
antioxidants. It has 389 mg sodium and 2663 mg potassium with a K/Na ratio of
84:6.
The diet has 134 mg of vitamin C and can meet both basic requirements and
help to promote iron absorption.
This diet provides 22, 634 µg total carotene of which 18,330µg is -carotene.
Even if the revised 8:1 -carotene to retinol conversion ratio were operative, this
diet would provide enough vitamin A.
Folic acid content is 286 µg total and about 96µg is free and these may
marginally meet the folate requirement. Folate rich food (vegetable) may have to
be introduced in this diet to bring the daily folate intake upto 400µg. So far
vitamin B12 is concerned, vegetarian diets with 200 ml of milk will provide only
0.3µg and 1 µg can be had if only animal food like egg or meat is included.
Dietitians should attempt to modify this diet for varying the energy intake for
individuals of different body weights with different activities.
While judging the adequacy of individuals with currently consumed diet it is
suggested that it should be combined with requirements adjusted for the
individuals according to their body weight.
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2
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