Essential amino acid requirements
dunns99 at erols.com
Thu Dec 16 14:19:16 EST 1999
Martin E. Lewitt wrote:
> In article <38592328.423B at erols.com>, Stuart Dunn <dunns99 at erols.com> wrote:
> >You think I didn't know that? I am not refering to protein digestion. I
> >was refering to the fact that amino acid breakdown produces urea and
> >other acids that are excreted through the urine.
> This is a fascinating area of physiology, since I can tell you would
> like to know more, let me recommend Devlin's "Biochemistry with
> Clinical Correlations". -- Martin
> Personal, not work info: Martin E. Lewitt My opinions are
> Domain: lewitt at swcp.com P.O. Box 729 my own, not my
> Hm phone: (505) 281-3248 Sandia Park, NM 87047-0729 employer's.
Here's the information I said I would give you:
Two of the most pervasive myths about vegetarian diets concern
Myth 1: It is hard to get enough protein on a vegetarian diet
Myth 2: Plant protein does not contain all essential amino acids and
you have to carefully combine plant foods in your diet in order to get
the "right" protein.
Both of these are false and are addressed in the summaries below.
From: molnar at utcs.utoronto.ca (Tom Molnar)
Subject: protein requirements
Message-ID: <D826CD.My8 at bisco.utcs.utoronto.ca>
The question of protein requirements and how to meet it with a
vegetarian diet comes up from time to time. I wish I had the time to
answer the question more fully, but I can't. I don't even have the
time to discuss it much. But I'll forward some notes I made for
myself when I gave a talk on protein requirements.
A few things to bear in mind:
+ I was generalizing, as in everything there are exceptions
+ I have met people who were able to do what I thought was
impossible, to be undernourished -- simply by choosing to
eat nutritionally imbalanced foods
+ Most importantly:
I am not a nutrition expert, I can make mistakes
and my opinions on diet, nutrition, human metabolism,
biochemisty and physiology can be dead wrong.
I probably won't be able to answer any questions that arise from these
notes since I am fairly busy these days.
Sources of info: Nutrition Recommendations: Health and Welfare Canada
Nutritional Biochemistry and Metabolism: M.C. Linder
The McDougall Plan: J.A. McDougall
Review of Medical Physiology: W.F. Ganong
Nutritional data: USDA Handbook #8.
What is protein?
it's one of the three macronutrients commonly identified as a
it represents nitrogen-containing compounds for which amino acids
are the basic structural units.
amino acids are small organic compounds containing at least one
amino group and an organic acid group. The differences between
amino acids lies in the differences between the amino acid side
proteins are the most abundant organic compound of the body. More
than fat, usually. Much more than carbohydrate. About 65% of the
total body protein lies in the skeletal muscles.
proteins function primarily in the growth and repair of body
tissue. Just about every cell in our body has a protein
component, and we are unable to synthesize new cells without the
requisite building blocks. Hair, nails, skin contain
protein. Blood contains plasma proteins; hemoglobin has a protein
component. Proteins are components of some antibodies. Many
hormones are proteins (like insulin). In fact, the protein
content of the average cell is 16% of its total mass.
there are more than 50,000 different proteins in our bodies.
These are all made from about 22 different amino acids. Our
bodies can synthesize 14 of these 22 amino acids, we cannot make 8
of them, and these 8 must come from food. These 8 are called the
essential amino acids. Sometimes we cannot synthesize other amino
acids and therefore they too must come from diet.
How much protein do we need? This has been studied extensively.
The studies try to determine how much protein is used and absorbed
before there is an excess. Usually this is done by determining
nitrogen balance. Nitrogen is a component of protein, and
measurements of nitrogen can be used to determine the amount of
amino acid quantity. By comparing the amount of nitrogen excreted
with the amount of nitrogen ingested, we can determine whether or
not protein is accumulating in the body, remaining at the same
level, or is decreasing. The nitrogen balance test compares
normal daily nitrogen losses (such as sweat, urine, feces, shed
skin, lost hair etc.) with intake. A postive balance means that
more nitrogen is being ingested than excreted, which means there
is tissue growth, such as that in a child. A negative balance
means that more nitrogen is being excreted than ingested, or more
protein is being degraded than synthesized in the body. This
represents a net loss of body protein.
Most of us have heard by now that the average protein requirement
is about 0.8 g dietary protein / kg body weight (about 56 grams of
protein for a 70 kg man). How did they arrive at that figure and
how much protein does the average diet provide? Note that this
figure varies, depending on where you look. In the end, the
variations are not that important since we get enough anyway.
The protein requirement is not really for protein per se, but for
amino acids. We break down all protein we eat into its
constituent amino acids and absorb them that way. That's why
diabetics can't just take insulin orally -- the insulin is a
peptide hormone, and it would be broken down into its amino acid
constituents as it passes through the digestive tract. It doesn't
matter what the source of the amino acid is, beef, egg, or
soybean. We really need to get the 8 essential amino acids from
diet and it doesn't matter where they come from. The often quoted
protein quality has nothing to do with the amino acid quality,
lysine from beans has the same chemical structure as lysine from
The protein requirement in adults is simply a replacement for
obligatory losses. Basically it amounts to keeping a leaky bucket
topped up. We lose protein through skin, sweat, hair, urine and
feces. We turn over a lot of protein in our bodies. We don't
rely on dietary protein to build all the proteins we need,
instead, we are very efficient at recycling our own tissues. In
fact, we recycle between 100 and 300 grams of our own protein
every day. We have an amino acid pool in our body from which we
take out amino acids to build new ones, and to which we add amino
acids by breaking down protein (endogenous and exogenous). We
have to eat regularly to keep adding to this pool, because we
don't have a store for proteins like we do for fats or
carbohydrate. So our protein requirement is just that which
supplies enough amino acids to replace that which is lost.
In the theoretical average 62.5kg person, about 240 g of protein
is synthesized and degraded daily. This process requires about 260
g of amino acid, of this amount about 1/6 must come from diet.
This means that only about 1/6 of the amino acids released by
endogenous protein degradation are not recycled. Where does all
this protein come from? A large part (maybe even more than half)
of it comes from the digestive juices, from the instestinal
mucosal cells, breakdown of muscle and other tissues, etc.
so what then is the requirement?
The minimum requirements for the essential amino acids are
variable, dependent on study. These numbers are more for academic
interest, since the Western diet, vegetarian or not, almost always
provides more than enough amino acids and sometimes far in excess
The specifics are:
Amino acid composition of the average mixed protein diet of
Canadians and comparison with the provisional amino acid
FAO/WHO/UNU 1985 provisional pattern for adults
(converted to mg/g protein by dividing the amino acid
requirement/kg by the recommended intake of egg or milk
protein/kg. For adults the recommended intake was 0.78g/kg)
diet mg/g mg/kg mg/g
Histidine - [8-12] [10-15]
Isoleucine 46.7 10 12.8
Leucine 79.1 14 17.9
Lysine 61.6 12 15.4
Cystine 34.1 13 16.7
Tyrosine 81.8 14 17.9
Threonine 38.4 7 9.0
Tryptophan 12.3 3.5 4.5
Valine 57.6 10 12.8
Taken from Nutritional Recommendations, 1990, Health and Welfare Canada.
Requirement of EAA (per kg body wt), mg/day
(From National Academy of Sciences,
Recommended Dietary Allowances, 9th ed. 1980)
Amino Infant Child Adult
4-6 mos 10-12 yr
Histidine 33 ? ?
Isoleucine 83 28 12 840 for
Leucine 135 42 16 1120 a
Lysine 99 44 12 840 70kg
Methionine & Cystine 49 22 10 700 adlt
Phenylalanine & tyrosine 141 22 16 1120
Threonine 68 28 8 560
Tryptophan 21 4 3 210
Valine 92 25 14 980
min prot req between 0.3 and 0.4 gm/kg
What affects these requirements? Are they always the same?
Definitly not. Our protein requirements can change dramatically
when we are injured or sick.
Now these are the minimum requirements for the amino acids
themselves, and proteins in foods contain variable amounts of
these amino acids. So requirements, expressed in terms of a
protein requirement not an amino acid requirement, have to take
into consideration things like variable quantities of amino acids,
and variable amino acid requirements.
They may double in the short term. Where does the body get this
extra supply when suffering from an illness -- especially if we
don't eat? From muscle, mostly. It may take a month or more to
restore the nutrients used up in the body while it fights off an
The protein requirement can also be affected by the amount of
carbohydrate in the diet. Nonessential amino acids can be made
from glucose, for example. Sometimes a significant amount is
made. Adequate carbohydrate supplies reduces the need for the
liver to synthesize glucose from amino acids. The liver will make
sure the blood sugar is at a minimum level, and it will break down
proteins to supply glucose if the glycogen reserves aren't kept at
an adequate level. Brain tissue and red blood cells use 140 to
150 grams of glucose over the period of a day for example. These
two tissues require glucose and the liver will make sure they get
it, either from food or from converting internal protein to sugar.
Long duration exercise can also lead to the burning of BCAAs. One
of the effects of carbohydrates, then, is to "spare" protein.
So what's the daily protein requirement? Well, the average
theoretical losses amount to about 0.34 g of protein per kg body
weight per day. Clearly a recommendation to replace this loss has
to have an adequate safety margin. With 2 standard deviations
added to this value, it comes to 0.45 g/kg per day of "ideal"
protein. Adding safety margins for digestibility and protein
quality, the requirement is thus in the region of 0.75g/kg.
Different countries have different recommendations. In Canada and
the U.S., the recommendation is about 0.8g/kg, while in Denmark it
is around 2g/kg and in Russia, it is even higher I think. I
believe the British recommendation is around 1.2g/kg, but am not
stating the requirement as a percentage of calories, the Canadian
RNI for protein is about 10% protein by calorie. They recommend
that protein make up 13 to 15 percent of the calories of the daily
diet. But remember, they also recommend that fats be kept to 30%
or less, leaving little room for carbohydrates. This is not what
many consider to be the optimal recommendation. Health and
Welfare Canada use what they view as a pragmatic approach I guess.
Protein levels in the diet: is it high enough?
one of the most common questions vegetarians hear is "So where do
you get your protein?". The answer is "from everything I eat".
It is a commonly held belief that we need lots of protein in our
diet and the foods that supply these proteins are meat, fish and
dairy products. Any diet that excludes these foods must be
deficient in protein. This is false. We've discussed that safe
and adequate level of protein intake for the average male adult is
about 56 grams. This can be just about met by eating nothing else
but 1 cup of rice and 1 cup of beans three times a day. One
package of Loblaw's tofu contains 53 grams of protein (not quite
1.5 cups). As I pointed out, it doesn't matter where the
requisite amino acids come from -- tofu can supply it just as well
as beef can, maybe even better.
an example of a study that compared protein intake is as follows:
Consumption of Essential Amino Acids and Protein by Vegetarians in the
Amino Acid Non-vegetarian Ovolacto-vegetarian Pure-vegetarian
Isoleucine 6.6 5.4 4.0
Leucine 10.1 8.2 6.0
Lysine 8.3 5.4 3.7
Phenylalanine and Tyrosine 10.3 8.8 7.0
Methionine and Cysteine 4.3 3.2 2.7
Threonine 5.0 3.8 2.9
Tryptophan 1.5 1.2 1.1
Valine 7.1 5.6 4.3
Total protein intake 121 97 82
(Linder, pp 90 -- from Hardage, 1966)
So we see that even the vegans in this study got more protein than
what about protein quality? Many people have been taught that
animal proteins are superior to plant proteins because animals
proteins have more essential amino acids per gram of protein, some
animal proteins are better digested than plant proteins and that
the amino acid profiles of animal proteins better match a
theoretical ideal protein than plant proteins.
It is true that animal proteins tend to have more essential amino
acids per gram of protein, in general, than plant protein. But so
what? We get too much protein in our diets anyway. A 12 oz
T-bone steak supplies a whopping 70 grams of protein. Pity our
poor kidneys. It's worthwhile to note that excessive amounts of
the sulphur containing amino-acids (methionine and cysteine) have
having adverse health effects. Generally only animal proteins
contain large quantities of this amino acid. Many studies indict
excessive protein intake by linking chronic diseases to excess
protein in the diet. There is also a limit to the amount of
protein we asimilate at any one time. This limit is around 25
grams. Excess protein is broken down and stored as fat. So are
animal proteins at an advantage? Maybe not. What do we get from a
12 oz T-Bone? Fat and probably sick.
What about the protein quality?
The amount of amino acids per gram of protein is called the amino
acid profile. There is an ideal protein that we use as a
reference to determine the "quality" of a protein and a few foods
Essential amino acid patterns of protein (mg/g)
Food TRY THR ISO LEU LYS MET+CYS PHE+TYR VAL
Ideal 11 35 42 70 51 26 73 48
soy 13 49 44 74 61 27 83 46
azuki 10 34 49 84 75 20 83 51
potato 16 36 40 59 60 29 81 56
h-milk 16 48 57 97 70 40 101 53
c-milk 14 45 60 97 79 34 96 66
eggs 16 49 62 87 67 56 97 72
rice 11 44 39 72 39 44 94 61
wheat 12 29 53 78 25 30 101 49
oats 13 35 42 83 45 57 84 61
This table should dispense once and for all the claim that plant
proteins are inferior to animal proteins because they are missing
or lacking some essential amino acids. All plant proteins contain
all essential amino acids in varying amounts. Anyone who says
that we have to eat a amino acid in particular ratios at each meal
doesn't really understand how the body deals with protein. What
we need to do is to replenish our amino acid pool, and the amino
acids do not, repeat, do not have to come from the same protein.
Not even from the same meal. Soy protein can supply the lysine at
lunch, wheat protein can supply the methionine at dinner.
Although we do not have a store of amino acids per se, we do have
an amino acid pool (circulating amino acids in the blood). The
half-life of amino acids in this pool vary, but the life of the
essential amino acids is at least 4 to 6 hours after digestion.
Protein synthesis goes on all the time and the source of amino
acids is the amino acid pool, and not necessarily the proteins you
absorb immediately following a meal. Eating replenishes the amino
acid pool, and there is enough of a supply that you don't have
worry about eating enough of a particular amino acid at each meal.
It all works out over the day. In the Western world, it is quite
difficult to eat a diet that results in a protein deficiency. In
Third World countries, where there are food shortages, protein
deficiency coupled with insufficient calories does occur with some
Digestibility. We're very good at digesting protein. We can
digest and absorb 70% - 90% of plant protein and 85% - 100% of
animal (or human) protein. Remember, we digest human protein all
the time -- our own tissues. We're very efficient at reclaiming
and recycling our own protein.
An example of the digestibility of foods is:
Food Digestibility of protein (%)
Meats, poultry, fish 85-100
Other legumes 93-85
(Linder pp. 90)
So our digestive system will not allow much protein to slip
through the body undigested. And it doesn't matter a great deal
what the source of the protein is. What does it matter if the
digestibility of wheat is 91% and that of eggs is 97% since the
amount of protein we eat is in excess of our minimum requirements
So what are good sources of protein if you decide to eliminate all
animal products from your diet?
While you get protein from just about all the foods you eat,
legumes and grains can supply significant quantities of protein in
the diet. Foods like TVP, tofu, seitan are concentrated sources
of protein. TVP is almost all soy protein, and seitan is
basically almost all wheat protein (gluten). Legumes, in general,
supply large quantities of protein (12 - 15 grams/cup). Nuts and
seeds also supply significant quantities of protein (like almonds
or pumpkin seeds). Grains like quinoa, amaranth, oats, wheat,
spelt are also very good sources of protein. Vegetables like
brocolli and potatoes supply significant amounts of protein. Even
a banana supplies a gram of protein.
Protein deficiency is not very common in the Western world.
Kwarshiorkor is fairly common in the Third World where it is often
accompanied by a deficiency of calories as well as protein
(marasmus). Protein deficiency as a result of diet, in our
society, can basically only happen during a restricted calorie
diet or by possibly following a very restricted diet such as a
What sorts of problems can longterm excess consumption of protein
lead to? Doctors like McDougall point out that excess protein in
diet can contribute (not cause) to osteoporosis, for example.
Diets high in protein are often also high in purines -- this can
lead to gouty arthritis.
Diets high in the sulpher containing amino acids might put people
at greater risk for cardiovascular disease.
Diets high in protein stress the kidneys, because the kidneys have
to get rid of the protein breakdown by-products, which can be very
toxic if left to accumulate.
How much is too much? Some experts feel that anything higher than
double the daily requirement is too high.
The protein requirements of humans can be readily met by a vegetarian
diet with no particular effort required to combine proteins or to
carefully select foods for each particular meal.
From: brian6 at vaxb.mdx.ac.uk (Lightbulb joke collector extraordinaire and
alt.fan.lightbulbs FAQ maintainer.)
Subject: Protein (all you ever wanted to know about...)
Date: 4 May 1995 07:58:47 GMT
Message-ID: <3oa1fn$e6o at epsilon.qmw.ac.uk>
Extracts from "Vegan Nutrition, a survey of research" by Gill Langley MA
Experts are still not entirely sure how much protein we need, and
estimates have often been revised in recent years. The national and
international organizations which advise on nutrient requirements
suggest standards which are calculated to meet or exceed the
requirements of practically everyone, explicitly taking into account
individual variation, and so these levels have a wide in-built safety
margin. In 1985 the World Health Organization (WHO) published revised
figures as follows:(1)
The WHO protein figures translate into 56g of protein a day for an
11.5 stone (75kg) man, and 48g for a 10-stone (64kg) woman. The
recommendations of the UK Department of Health and Social Security
(DHSS) are slightly higher, at about 68g a day for sedentary or
moderately active men, and 54g a day for women (2). Both these
official recommendations suggest that eating 10% of our daily energy
as protein will provide an adequate amount. The NACNE report (3)
proposes a protein intake of 11%. National and international
recommendations for protein intake are based on animal sources of
protein such as meat, cow's milk and eggs. Plant proteins may be less
digestible because of intrinsic differences in the nature of the
protein and the presence of other factors such as fibre, which may
reduce protein digestibility by as much as 10%. Nevertheless, dietary
studies show the adequacy of plant foods, as sole sources of protein
(see Combining Proteins below), as does the experience of healthy
vegans of all ages.
The main protein foods in a vegan diet are the pulses (peas, beans and
lentils), nuts, seeds and grains, all of which are relatively energy
dense. As the average protein level in pulses is 27% of calories; in
nuts and seeds 13%; and in grains 12%, it is easy to see that plant
foods can supply the recommended amount of protein as long as the
energy requirements are met.
People are not Rats
Tradition has it that plant proteins are of a poorer quality than
animal proteins, because the essential amino acids are present in
proportions which may not be ideal for human requirements. In the
early years of research into protein quality this belief derived from
experiments with laboratory rats, when it became clear that amino acid
supplementation of a plant source of protein improved its biological
value to the point where it would support the growth of weaning
rats. The parameters of these experiments were set in such a way that
differences in the quality of plant and animal proteins were
maximised; the second major problem is that rats and humans have
different nutritional requirements (4).
The weanling rat grows, relatively, at a much faster rate than the
human infant and therefore requires a more concentrated source of
nutrients, including protein. A comparison with human milk makes the
difference quite clear; protein comprises only 7% of the calorie
content of breast milk, while rat milk contains 20% protein. If
weanling rats were fed soley on human milk, they would not
thrive. Using the same logic as was applied in the early experiments,
it could be argued from this that breast milk is also inadequate for
Some early studies further demonstrated the differences in nutritional
requirements between rats and humans. In 1955 (5) an experiment with
three male volunteers showed that the amino acid cystine is able to
substitute for 80-89% of the body's requirement for another essential
amino acid, methionine, whereas in rats the substitution value is only
Although the terms 'first-class' and 'second-class' proteins are no
longer used, in some circles the belief persists that a vegan diet,
containing only plant proteins, may be inadequate. This is because
cereals, nuts and seeds contain less of the amino acid lysine, while
being high in methionine; and pulses are rich in lysine but contain
less methionine. This has given rise to concern that the amino acid
present in lower amounts in each food will limit the availability to
the body of the others, and the suggestion has been made (6), and
adopted quite widely - even among vegans - that complementary protein
foods, such as beans and grains, should be eaten at each meal in order
to enhance amino acid availability. Vegetarians are also sometimes
advised to ensure that they complement vegetable proteins with dairy
foods. Are these precautions necessary?
Protein combining may reduce the amount of protein required to keep
the body in positive protein balance (6), but several human studies
have indicated that this is certainly not always the case. For
example, over a 60-day period seven human subjects were fed diets in
which protein was derived solely either from beans, corn and refined
wheat; beans, rice and refined wheat; or a combination of the plant
foods with the addition of cow's milk (8). All subjects remained in
positive nitrogen balance (a measure of the adequacy of dietary
protein), and there were no significant differences in nitrogen
balance between the subjects eating only plant foods and those whose
diet was supplemented with milk.
Another study looked at the nutritive value of a plant-based diet in
which wheat provided 76% of the protein (9). The aim was to determine
whether this regime could be improved by adding other sources of plant
protein - such as pinto beans, rice and peanut butter. The diets were
entirely vegan, containing only 46g of protein, and were fed to 12
young men over a 60 day period, during which they continued their
normal daily activities. The researchers found that all subjects
remained in nitrogen balance, and that replacement of 20% of the wheat
protein with beans, rice or peanut butter did not result in
significant changes in the levels of essential amino acids in the
Even more startling perhaps were the findings of a 59-day
investigation with six male subjects who consumed diets in which
virtually the sole source of protein was rice (10). At two protein
levels (36g and 48g per day) the diets comprised rice as the sol
source of protein, or regimes where 15 and 30% of the rice protein was
replaced with chicken. The partial replacement of rice with chicken
protein did not significantly affect the nitrogen balance of the
volunteers (in contrast to earlier experiments with rats which showed
that a rice diet did not sustain normal growth). In this human study,
even on the low-protein diet rice as the sole source provided between
2 and 4.5 times the WHO-recommended amounts of all essential amino
acids, except lysine - of which it supplied 1.5 times the suggested
level. On the higher protein diet, rice alone provided between two and
six times the essential amino acid levels suggested by the WHO, and
all subjects were in positive nitrogen balance.
When cornmeal was fed as virtually the sole source of protein to ten
male volunteers during a 100-day study it was found that at an intake
of 6g of nitrogen per day (approx. 36g protein) not all the subjects
were in positive nitrogen balance (11). Yet all the essential amino
acids were eaten in amounts which met or exceeded standard
requirements, with the exception of tryptophan - of which 91% was
provided. These results suggest that on a corn protein diet, non
specific nitrogen is the first limiting factor, not lack of esssential
The 1988 position paper of the American Dietetic Association (12)
emphasized that, because amino acids obtained from food can combine
with amino acids made in the body it is not necessary to combine
protein foods at each meal. Adequate amounts of amino acids will be
obtained if a varied vegan diet - containing unrefined grains,
legumes, seeds, nuts and vegetables - is eaten on a daily basis.
These and other similar experiments show clearly that diets based
solely on plant sources of protein can be quite adequate and supply
the recommended amounts of all essential amino acids for adults, even
when a single plant food, such as rice, is virtually the sole source
of protein. The American Dietetic Association emphasizes that protein
combining at each meal is unnecessary, as long as a range of protein
rich foods is eaten during the day.
1. Food and Agriculture Organization/ World Health Organization/
United Nations University (1985). 'Energy and protein requirements',
WHO Technical Report Series 724. Geneva, WHO.
2. Department of Health and Social Security (1979). Recommended Daily
Amounts of Food Energy and Nutritients for Groups of People in the
United Kingdom. London, HMSO.
3. National Advisory Commitee on Nutrition Education
(1983). Proposals for Nutritional Guidelines for Health Education in
Britain. London, Health Education Council.
4. Vaghefi, S.B., Makdani, D.D. and Mickelsen, O. (1974). 'Lysine
supplementation of wheat proteins, a review', Am. J. Clin. Nutr. 27,
5. Rose, W.C. and Wixom, R.L. (1955). 'The amino acid requirements
of man. XIII The sparing effect of cystine on methionine
requirement', J. Biol. Chem., 216, 763-773.
6. Lappe, F.M. (1976). Diet for a small planet. New York, Ballantine
7. Kofranyi, E., Jekat, F. and Muller-Wecker, H. (1970). 'The
minimum protein requirements of humans, tested with mixtures of whole
egg plus potatoes and maize plus beans', Z. Physiol. Chem., 351,
8. Clark, H.E., Malzer, J.L., Onderka, H.M., Howe, J.M. and Moon, W.
(1973). 'Nitrogen balances of adult human subjects fed combinations
of wheat, beans, corn, milk, and rice', Am. J. Clin. Nutr., 26,
9. Edwards, C.H., Booker, L.K., Rumph, C.H., Wright, W.G. and
Ganapathy, S.N. (1971). 'Utilisation of wheat by adult man; nitrogen
metabolism, plasma amino acids and lipids', Am. J. Clin. Nutr., 24,
10. Lee, C., Howe, J.M., Carlson, K. and Clark,
H.E. (1971). 'Nitrogen retention of young men fed rice with or without
supplementary chicken', Am. J. Clin. Nutr., 24, 318-323.
11. Kies, C., Williams, E. and Fox, H.M. (1965). 'Determination of
first limiting nitrogenous factor in corn protein for nitrogen
retention in human adults', J. Nutr., 86, 350-356.
12. Havala, S. and Dwyer, J. (1988). 'Position of the American
Dietetic Association: vegetarian diets - technical support paper',
J. Am. Diet. Assn., 88, 352-355.
Frances Moore Lappe, author of DIET FOR A SMALL PLANET was one
of the influential voices that originally promulgated the "gospel" of
protein complementarity. After it was found to be unnecessary, she
corrected herself in a later edition of her book.
>From DIET FOR A SMALL PLANET, Tenth Anniversary Edition, Frances
Moore Lappe, p 161-162:
"When I first wrote DIET FOR A SMALL PLANET in 1971, the idea that
people could live well without meat seemed much more controversial
than it does today. I felt I had to prove to nutritionists and
doctors that because we could combine proteins to create foods equal
in protein usability to meat, people could thrive on a nonmeat or
low-meat diet. Today, few dispute that people can thrive on this kind
of diet. In fact, more and more health professionals are actually
advocating less meat precisely for health reasons, reasons I discussed
in 'America's Experimental Diet.'
"In 1971 I stressed protein complementarity because I assumed that the
way to get enough protein (without consuming too many calories) was to
create a protein as usable by the body as animal protein. In combatting
the myth that meat is the only way to get high-quality protein, I
reinforced another myth. I gave the impression that in order to get
protein without meat, considerable care was needed in choosing foods.
Actually, it is much easier than I thought.
"With three important exceptions, there is little danger of protein
deficiency in a plant food diet. The exceptions are diet very heavily
dependent on fruit or on some tubers, such as sweet potatoes or
cassava, or on junk food (refined flours, sugars, and fat).
Fortunately, relatively few people in the world try to survive on
diets in which these foods are virtually the sole source of calories.
IN ALL OTHER DIETS, IF PEOPLE ARE GETTING ENOUGH CALORIES, THEY ARE
VIRTUALLY CERTAIN OF GETTING ENOUGH PROTEIN." (italics author's)
BUT HOW DO YOU GET ENOUGH PROTEIN ?
How important a question this is for many potential vegetarians ! Our
culture seems to be obsessed with obtaining enough protein. And yet
protein is one of the easiest nutrients to get. By an inappropriate
choice of foods, a person might be deficient in vitamins A or C ; but
it is almost impossible to be protein deficient on a calorically
adequate diet. To see why this is so, we need to look at protein
requirements as a percentage of calories.
Protein as a percentage of calories
Protein, fat, and carbohydrate - the three major components of common
all contain calories, in about this ratio : -
1 gram of protein = 4 calories
1 gram of carbohydrate = 4 calories
1 gram of fat = 9 calories
Thus, if a potato weighing 100 grams contains 76 calories and 2.1
grams of protein, we say that it contains 2.1*4 = 8.4 calories as
protein, or about 11% calories as protein. According to the National
Research Council, an adult male requires 2700 calories and 56 grams of
protein per day. The 56 grams of protein represent 224 calories, or
about 8.3% of calories as protein. For the adult female, the figure is
about the same : 2000 calories and 44 grams of protein, or about 8.8%
of calories as protein.
If wheat has 17% of calories as protein, potatoes 11%, broccoli 45%,
corn 15%, and so on, then ALL OF THESE FOODS PROVIDE ENOUGH PROTEIN ON
A CALORICALLY ADEQUATE DIET, EVEN IF YOU EAT NOTHING BUT POTATOES,
WHEAT, AND BROCCOLI. In fact, of the common plant foods, almost all
provide more than 10% of calories as protein. Only the fruits, as a
rule, contain less; but this is not going to be a problem unless one
is trying to live on an all-fruit diet.
* PROTEIN CONTENT OF SOME COMMON *
* PLANT FOODS (100 GRAM DRY PORTION) *
* FOOD CALORIES % OF CALS *
* AS PROTEIN *
* BROCCOLI 32 45 *
* CARROT 42 10 *
* CORN 96 15 *
* POTATO 76 11 *
* SQUASH 19 23 *
* CUCUMBER 15 24 *
* SWEET POTATO 114 6 *
* TOMATO 22 20 *
* PINTO BEANS 349 26 *
* CHICK PEAS 360 23 *
* LENTILS 340 29 *
* PEANUTS 564 18 *
* BARLEY 348 11 *
* RICE 360 8 *
* RYE 334 14 *
* WHEAT 330 17 *
* ALMOND 598 12 *
* WALNUT 628 13 *
* APPLE 56 1 *
* BANANA 85 5 *
* ADULT RDA 2000-2700 8-9 *
"But what about protein complementarity ?"
In 1971, a revolutionary new book came out espousing the virtues of a
meatless diet. It became a million-copy bestseller and convinced many
people to try vegetarianism or become vegetarians. That book was DIET
FOR A SMALL PLANET by frances Moore Lappe.
In her book, Lappe put forward as her central concept the idea of
"protein complementarity" - the idea that vegetarians should eat
different kinds of proteins at a single meal in order to get the same
quality of protein which was found in meat. Countless thousands of
vegetarians thereafter referred to Lappe's charts and tables and
struggled to understand the intricacies of balancing tryptophan,
lysine, methionine, and all the other amino acids. The basic idea was
this: while meat contains all of the amino acids, plant foods were
deficient in one or more of the eight "essential" amino acids.
Therefore, balance plant foods weak in one amino acid but strong in a
second amino acid, with other plant foods strong in the first but weak
in the second. Simple, right ? Well, simple to some people, but not
so simple to others, who eventually gave up the effort and went back
to a meat-based diet out of fear of missing one or another of the
amino acids. And yet the central thesis of this best-selling book,
one which even today many vegetarians believe in, is false. there's no
question that you need all of the amino acids. But virtually all plant
foods have ALL of the essential amino acids; and not only are the
amino acids there, they are present in more than enough quantity to
meet the needs of normal adults, if you are on a calorically adequate
diet. It's true that plant foods have more of the requirements of
amino acids than of others. Rice is strong in tryptophan, methionine,
and valine, and weak in isoleucine and lysine. But rice protein
sufficient to provide 100% of our quantitive protein needs, also
provides 265% of the adult male requirement for lysine and 266% of
that for isoleucine. (It provides 400% or more of all of the others.)
The same is true for virtually all other plant foods. In fact, some
plant foods which do not quite provide the requirement for total
protein, such as sweet potatoes, DO provide the minimum requirement
for ALL of the essential amino acids.
Rats and people
The whole idea of "protein complementarity" got started in 1914 when
Osborne and Mendel published a paper on rat nutrition. They noticed
that baby rats fed on a plant food diet did not grow as fast as other
rats who ate the same diet plus a lysine supplement. Conclusion: these
plant foods needed a lysine supplement.
Unfortunately, the nutritional requirements of rats and humans are
quite different, and this was quickly demonstrated by experiments on
humans. Studies in which humans have been fed wheat bread alone, or
potatoes alone, or corn alone, or rice alone, have ALL shown that
these plant foods contain not only enough protein, but enough of ALL
of the essential amino acids, to support growth and maintenance of
healthy adults. Particularly striking were the experiments involving
rice: not only was the rice protein more than adequate, it was
adequate when only about 2/3 of the calories were provided through the
rice. This means that the actual requirement of protein for most
individuals is actually less than 8% of calories as stated by the
National Research Council; the NRC has padded its figures with a
"safety factor" which many individuals do not need.
A few sample plant foods are shown with their "limiting amino acid"
content in the accompanying table. (Limiting amino acids are the amino
acids the food contains the LEAST of in relation to human nutritional
* LIMITING AMINO ACID CONTENT *
* OF SELECTED "LOW-PROTEIN" FOODS *
* % OF RDA *
* LIMITING IN 56G PROTEIN *
* FOOD AMINO ACIDS FOR 70KG MALE *
* CORN LYSINE 484% *
* TRYPTOPHAN 510% *
* RICE LYSINE 265% *
* ISOLEUCINE 266% *
* WHEAT LYSINE 178% *
* POTATO ISOLEUCINE 241% *
* SULPHUR-CONTAINING AA'S 145% *
* CARROT TRYPTOPHAN 194% *
* SULPHUR-CONTAINING AA'S 190% *
Protein deficiencies ?
There ARE some ways you can become protein deficient, but it's pretty
hard. One way is not to get enough food. We sometimes see people in
famine areas with bloated bellies who ARE suffering from protein
deficiency. they are also suffering from deficiencies of calories,
iron, calcium, and vitamins A through Z. In short, they are "starving
to death," and their problem is not so much lack of protein as it is
lack of everything.
Another way to become protein deficient is to get almost all of your
calories from alcohol and/or sugar. Sugar contains no protein ! Hard
liquor contains virtually no protein (beer contains very small
amounts.) So if you are an alcoholic sugar junkie, you may be in
danger of protein deficiency. Another possible source of deficiency is
that infants may be fed foods which they cannot digest.
Because of the sufficiency, or overabundance, of plant protein, animal
products (milk, cheese, and eggs as well as meat, fish, and poultry)
are completely unnecessary for adequate protein nutrition. Breast
milk, incidentally, which has provided human infants with adequate
protein for hundreds of thousands of years, provides 6% of calories as
protein - far less than that of whole cow's milk, which contains 22%
of calories as protein.
Not only is plant protein sufficient, it is often SUPERIOR to animal
protein. Excessive protein consumption is now strongly linked to bone
weakness and osteoporosis. Studies done on calcium loss have shown
that as protein consumption increases, so does calcium loss. Not only
that, the protein in meat (which is higher in the sulphur-containing
amino acids) causes a GREATER calcium loss than the same quantity of
protein in soya beans ! So for preventing calcium loss and the
possibility of osteoporosis, plant protein is superior to animal
THE WORD ON PROTEIN COMPLEMENTARITY IS: FORGET IT. The whole idea that
this is necessary is a myth. Frances Moore Lappe has now essentially
reversed herself on this issue, saying that getting enough protein "is
much easier than I thought." It's good to get a variety of foods,
because you need all the various vitamins and minerals - not because
of protein. If you get plenty of a variety of plant foods, regardless
of your combining techniques (or lack thereof,) and you get enough
calories (not too difficult for most of us,) it's almost impossible to
be protein deficient. Protein is one of the easiest nutrients to get.
- Written by Keith Akers.
Copy-typed by BRIAN from a leaflet produced by the Vegetarian Society of
Colorado, sent to me by Larry Kaiser of the "Veggie" list.
I hope you are convinced that low protein diets are safe and that plant
protein is just as useful as animal protein.
More information about the Proteins