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Unit 11
PROTEIN
Objectives
 To realise that protein is a non-problem in western countries
 To discover that most people in western countries eat too much protein and
that their diet is also high in animal fat, sugar and salt
 To understand the problems associated with a diet that is high in protein
 To be aware of protein synthesis and turnover
 To understand that vegetable protein from a variety of sources is as good
as meat protein and in many aspects is superior
INTRODUCTION
Ever since the discovery of this nitrogen-containing chemical in 1839 by the Dutch
chemist Gerhard Mulder, protein has loomed as the most sacred of all nutrients. The
word protein comes from the Greek word proteios, which means of prime
importance. A nitrogen containing food without which life is impossible.17
Proteins make up a large part of the machinery of the living body. It is a vital part of
every cell in the body, including those in muscles, the heart, liver and kidneys, blood
cells, skin, hair and nails, teeth and bones14.
Too much protein is unnecessary but you do need some. Whenever growth is
occurring, new cells are forming and protein requirements are increased. A child
requires a higher percentage of protein to body weight than an adult. Protein needs
increase also during pregnancy to provide for the needs of the growing baby14.
Once growth stops, protein is still needed to replace cells lost through wear and tear
of normal living - repair and maintenance14.
Protein is also used by the body to make enzymes, antibodies which fight infection,
haemoglobin (which carries oxygen in the blood) and hormones such as insulin 14.
If you are worried about getting enough protein on a plant based diet, you shouldn’t
be. Since proteins are in practically every food we eat, getting enough protein on a
vegetarian diet is easy. Although non-vegetarian diets typically provide more protein,
vegetarian diets are well able to meet and exceed the recommended daily
requirements14.
PROTEINS AND MUSCLES14
Some body builders almost worship protein, believing that an ample supply will
produce the biceps and triceps they desire. It won’t! Muscles do contain protein, but
that does not mean that filling yourself with extra quantities of protein will enlarge
them. Muscles develop when they are used, and the ideal fuel for muscles is
complex carbohydrate, not protein.
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Because the average Australian diet contains at least twice as much protein than the
body’s actual need, the modest amount of extra protein a body builder may need is
adequately supplied. Ordinary physical activity does not require extra protein, as the
muscles use carbohydrates and fat as fuel in preference to protein. Taking extra
protein in the form of amino acid supplements will not produce extra muscle growth.
WHAT ABOUT EXCESS14?
The fashion for high-protein diets has been blamed for the development of big beefy
people. Early puberty may also be partly related to eating large quantities of protein.
One of protein’s problems is the company it keeps. Slabs of steak, hamburger
mince, hearty helpings of meats in stews, cheeses, and breakfasts of sausages,
bacon and eggs will contribute lots of protein but also stacks of saturated fat.
Another problem with excess protein is that urinary excretion of calcium is increased,
which long term, can increase the risk of osteoporosis.
Once the body has met its protein requirements, any excess protein is converted to
body fat14.
AMINO ACIDS, THE BUILDING BLOCKS OF PROTEIN4
Proteins consist of long chains of smaller units called amino acids. After digestion,
proteins are broken down into their separate amino acids. There are 20 common
amino acids that the body uses. All foods contain a mixture of these amino acids.
They are combined in various combinations to make body proteins, much the same
as we make words with letters of the alphabet. They are linked by bonds to form
ribbon-like peptide chains.
Of the 20 amino acids there are 9 essential amino acids. Defined in nutritional terms,
this means that the body cannot make the essential ones, so they must be supplied
from the food we eat.
All amino acids are necessary for good health. The body can manufacture the 11
non-essential amino acids, if the essential amino acids are supplied in adequate
amounts4.
PROTEIN SYNTHESIS AND TURNOVER16
Body proteins are not retained for life but are continually being broken down and
replaced. Some proteins such as enzymes are turned over quickly and may have a
life span as short as a few hours. Red blood cells, by contrast, have an average life
span of about 2 months. Proteins with the lowest turnover rate are those of the
connective tissue which holds the body together. These are collagen and elastin of
tissues such as tendons, muscle sheath and the non-mineral part of the bone.
Protein turnover involves breakdown and resynthesis. This breakdown process is
accomplished by intracellular enzymes which break down the proteins into amino
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acids. These are then added to the pool of amino acids and are available for
resynthesis into protein.
Total protein turnover amounts to 300 gram to 400 gram per day and is substantially
more than the normal daily protein intake which averages about 100 gram a day.
Body protein turnover smoothes out the supply of amino acids supplied by food.
USES OF PROTEIN IN THE BODY4
1. Protein is synthesised in all cells of the body, and is necessary for growth and
maintenance. Each cell selects the specific amino acids it needs to function. Not
all cells manufacture the same proteins. The amino acids are assembled in the
order necessary for the protein required by that cell.
2. Digestive enzymes and cellular enzymes are made of protein. They act as
catalysts, that is, they help reactions take place. There may be as many as 1000
enzymes in a single cell.
3. Proteins play a role in the immune system and the formation of antibodies.
4. Proteins help regulate the body’s fluid, salt and acid balance.
5. Protein can be used as energy, but is not an efficient source:
a. It has to be broken down in the liver to glucose.
b. The extra waste of nitrogen and sulfur has to be cleared by the kidneys.
6. Haemoglobin carries oxygen in the blood and is made up of a long sequence of
amino acids with iron.
7. Hair and fingernails are made of protein; the skin and cell membranes contain
proteins.
8. Proteins are necessary for the transportation of fats and cholesterol in the blood.
9. Collagen is the protein part of the connective tissue.
10. Muscles that move the body are made of protein4.
ANIMAL VERSES VEGETABLE PROTEIN14
Animal protein foods such as meats, fish, eggs and dairy products contain all the
essential amino acids.
Vegetable protein foods are usually low in one or two. However combinations of
vegetable foods can easily supply the entire range of amino acids.
Cereals tend to be low in the amino acid lysine but adequate in the amino acid
methionine. Legumes are adequate in lysine but low in methionine. Therefore, the
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amino acid profiles of the cereals and legumes complement each other so that a
cereal-legume combination provides high-quality protein. It is important that
wholegrains be used rather than refined grains, because the protein quality of a grain
is reduced significantly when it is refined. For example, the protein quality of white
flour is 22% less than that of whole wheat.
Clearly, the quality of protein eaten at each meal is important but not critical since the
endogenous protein (internally derived) supplies a significant amount of essential
amino acids. For the different types of protein (cereal/legumes/vegetable/nut/seed)
to complement each other, they should be eaten during the same day, but not
necessarily within the same meal. This allows for flexibility in food preferences and
removes the concern about whether each meal contains properly balanced protein
sources.
It is recommended that people following a vegetarian diet should include a variety of
plant foods in their meals throughout the day. Vegetarians rarely have a problem
obtaining sufficient protein. However anyone who tries to live on a very restricted
diet, such as fruitarians (who eat nothing but fruit), can become deficient in protein.
As with most things, it is only the extremes which produce problems14.
SOY IS UNIQUE6,10
Soy is a plant protein with a difference. It is the only plant protein that is of high
nutritional quality, and has adequate levels of all the essential amino acids8.
In addition, soy protein contains the isoflavonoid genistein and similar substances
that act as phytoestrogens and inhibit tumor growth1,12, lower blood cholesterol
levels, decrease the risk of heart disease7, stroke11,12, cancer9 and osteoporosis2,3,11.
HIGH PROTEIN DIET (ANIMAL PROTEIN)4
Diets containing high intakes of animal protein contribute to the following problems:
1. High in saturated fat, 40% of the energy value in red meat comes from fat.
2. High in dietary cholesterol, which comes only from animal flesh and products. The
use of animal protein, with its typically high content of saturated fat and
cholesterol, increases the risk of cardiovascular disease.
3. The overall diet is often low in fibre (foods from animal origin contain no fibre.)
4. It is less economical, due to the high cost of meat.
5. If the protein content of diet is high, there will be a loss of calcium through the
kidneys, increasing the risk of osteoporosis15.
6. With a higher intake of protein, there is usually a lower intake of fruit and
vegetables. This can lead to other nutritional deficiencies as the requirements for
many vitamins and minerals are increased with a high protein diet.
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HIGH PROTEIN LIQUID DIETS4
There are several high protein liquid diets available on the market which have proven
popular for slimming and cleansing programs. However, it is difficult to maintain a
balanced nutritional intake on this type of diet. The following statement is from the
Australian National Health and Medical Council5:
“Council noted with concern, overseas reports of deaths resulting from the use of
high protein liquid diets. These were products marketed in both liquid and powder
form, composed essentially of protein or protein hydrolyses, which were intended for
use in weight reduction regimes.
As there are a number of these products on sale in Australia, Council wishes to alert
the public to possible hazards, particularly if they were used as a sole item in the diet.
In particular, persons taking medication, pregnant and nursing mothers, Infants and
children should avoid these products. The alleged benefits of these protein diets
remains unproven and research data on the safety and long term use of protein
products as the principle or only source of nutrients for weight control were
inadequate.
Council recommended the establishment of proper dietary and exercise regimes for
weight reduction as being the only long term effective measures for weight control5.”
PROBLEMS WITH PROTEIN DEFICIENCY4
1.
Kwashiorkor is a disease caused by protein deficiency. It is found mainly in
developing countries where the staple diet is high in energy but low in protein.
Symptoms observed:
a. Tissue wasting
b. Hair becomes reddish, thin
c. Poor resistance to disease
d. Edema – swollen stomach, lower arms and legs
2.
Marasmus (starvation) is generally associated with a total energy deficiency
including protein.
Symptoms observed:
a. Extreme tissue wasting
b. Sunken eyes
c. Hair becomes reddish, thin
d. Poor resistance to disease
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HOW MUCH DO WE NEED16?
The recommended daily intake (RDI) for protein can vary according to the country in
which you live. The RDI for Australia is the same as the World Health
Organisation. Adults, 0.75 grams of protein for each kilogram of body weight16.
WHO Protein RDI – 198513
Adults
Pregnancy
Lactation
Children
0-6 months
6 months +
0.75 gm/kg body weight
add 6 grams per day
add 17.5 grams per day
add 13 grams per day
3-6 months
6-9 months
9-12 months
1-2 years
3-5 years
5-12 years
13-15 years
16-19 years
1.85 gm/kg body weight
1.65 gm/kg body weight
1.50 gm/kg body weight
1.20 gm/kg body weight
1.10 gm/kg body weight
1.00 gm/kg body weight
0.95 gm/kg body weight
0.80 gm/kg body weight13
ADVANTAGES OF PLANT PROTEIN6
1. A number of advantages can be associated with plant proteins. Firstly, the lower
protein intake of vegetarian diets may be beneficial, since an excess of protein,
especially animal protein rich in sulfur amino acids, can cause urinary calcium
losses, increasing the risk of osteoporosis.
2. Excess protein can negatively impact kidney function in persons with previous
renal disease.
3. In plant foods, protein is packaged with fibre, carbohydrates, vitamins and
minerals and a host of phytochemicals, plus the fat content is usually low.
4. Good for the environment6
The use of plant protein is also a vote for the environment. Present methods of
meat production harm the environment. Over grazing can produce soil erosion
and increase the risk of desertification.
Feeding grains and legumes to animals to produce beef, pork and other animal
proteins involves great losses of protein and energy. For example, only 4% of the
calories consumed by beef cattle are returned in beef, while 15% of the energy
consumed by dairy cattle shows up in the milk they produce. Furthermore, it
takes about 7 to 10 kilos of plant protein to produce one kilo of animal protein.
Clearly following a vegetarian lifestyle conserves the world’s food resources.
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Also a plant based diet with an emphasis on whole grains and legumes conserves
land, water and energy resources. It takes up to 10 times less land to feed people
on plant foods than animal products. An acre of land can produce 20 kilos of
protein as beef, or 121 kilos of protein as wheat, or as much as 200 kilos as
soybeans.
Land animal-based intensive agriculture requires relatively large amounts of
water. It takes about 100 times more water to produce 1 kilo of animal protein
(beef) than 1 kilo of plant protein. Most of the water is used to produce animal
feed as the animals themselves consume very little water.
5. Economic reasons6
Plant protein is a lot more economical than meat. Beans, tofu and lentils are
considerably cheaper than steak, fish or chicken.
6. Food safety factors6
Fresh beef, chicken, pork, fish and other animal foods are highly perishable foods,
while grains and legumes can be stored and easily transported with much less
spoilage. The risk of bacterial contamination and food poisoning from eating
animal foods is several orders of magnitude greater than from eating plant foods.
Every year hundreds of Australians become sick and die from animal products
contaminated with Salmonella, E. coli, Campylobacter and other organisms.
PROTEIN CONTENT OF PLANT FOODS6
Food item
Grams of protein
½ cup tofu
10
½ cup cooked legumes
7.5
1 cup cooked pasta
7
1 cup soy milk
8
30 grams almonds
6
1 cup cooked oatmeal/rolled oats
5
1 cup cooked rice
5
1 medium baked potato
5
2 slices wholemeal bread
5
½ cup peas
4
1 tbsp peanut butter
4
1 cup vegetable soup
3
½ cup broccoli
2.5
200 grams soy yoghurt
9
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CONCLUSION
We can safely say that a plant-based diet can meet the protein needs of healthy
individuals, provided the diet contains an adequate level of calories and that it
consists of a variety of unrefined grains, legumes, and vegetables. Dietary surveys
confirm that vegetarian diets contain both the quantity and quality of protein to
maintain optimal health6.
The vegetarian lifestyle has much to commend it. Studies of vegetarians have shown
that they have a lower prevalence of a number of the diseases that are now common
in the affluent societies of Western countries. Such diseases include obesity,
coronary heart disease, hypertension and diet related cancers.
REFERENCES:
1. Aldercreutz H;
SOYBEAN PHYTOESTROGEN INTAKE AND CANCER RISK
Journal of Nutrition 1995; 125(3S) 757S-770S
2. Anderson J, Garner S;
THE EFFECTS OF PHYTOESTROGENS ON BONE
Nutr Res 1997;17(10):1617-32
3. Breslau N;
RELATIONSHIP OF ANIMAL PROTEIN–RICH DIET TO
KIDNEY STONE FORMATION AND CALCIUM METABOLISM
Journal of Clin Endocrinol Metab 1988;66(1):140-146
4. Butler T, Butler D, Stanton H;
VEGETARIAN COOKING DEMONSTRATOR’S MANUAL –
2nd EDITION
Adventist Health Department &
Sanitarium Nutrition Education Service, 1995: E37-E45
5. Commonwealth Department of Health;
1986 NUTRITION POLICY STATEMENTS: 57
6. Craig W;
NUTRITION AND WELLNESS
Golden Harvest Books Berrien Springs Michigan 1999:27-32
7. Department of Health and Human Services, Food and Drug Administration;
FOOD LABELING: HEALTH CLAIMS; SOY PROTEIN AND
CORONARY HEART DISEASE
October 1999
8. Henley E, Kuster J;
PROTEIN QUALITY EVALUATION BY PROTEIN DIGESTIBILITY –
CORRECTED AMINO ACID SCORING
Food Tech 1994;48(4): 74-77
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9. Messina M, et al;
SOY INTAKE AND CANCER RISK:
A REVIEW OF THE IN VITRO AND IN VIVO DATA
Nutr Canc 1994;21: 113-31
10. Sanitarium Nutrition Education Service;
ENJOYING SOY FOR GOOD HEALTH
Sanitarium Health Food Company April 2000
11. Setchell K, Cassidy A;
DIETARY ISOFLAVONES: BIOLOGOICAL EFFECTS AND
RELEVANCE TO HUMAN HEALTH
Journal of Nutrition 1999; 129: 758S-767S
12. Setchell K;
PHYTOESTROGENS: THE BIOCHEMISTRY, PHYSIOLOGY,
AND IMPLICATIONS OF HUMAN HEALTH
OF SOY ISOFLAVONES
American Journal of Clinical Nutrition 1998;68(suppl):1333S-46S
13. Shils N, Young V;
MODERN NUTRITION IN HEALTH AND DISEASE - 7th Edition
Lea & Febiger 1988: 29
14. Stanton R;
EATING FOR PEAK PERFORMANCE
Allen & Unwin Australia Pty. Ltd, North Sydney, NSW
1988: 87-89
15. Swannell R;
OSTEOPOROSIS – A COMMON BONE DISORDER
Good Health January 1979
16. Wahlqvist M. L; FOOD AND NUTRITION - Australia and New Zealand 2nd Edition
Allen & Unwin Pty Ltd Crows Nest NSW 2002: 212-226
17. Campbell C. T; THE CHINA STUDY – 1st edition
Benbella Books, Dallas, 2006: 27,
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