In recent decades, vegetarianism has shed its image as an offbeat
lifestyle choice and attracted many Americans who want to take advantage
of the benefits offered by plant-based eating. These people are
adopting a vegetarian diet to improve their health, avoid the chemicals
used in animal foods, reduce food costs, conserve natural resources,
adhere to religious disciplines, and respect animal life. More than
7 million Americans now eat a vegetarian diet for these reasons
Despite these gains, the US remains a leading consumer of meat;
and the rationale for vegetarian eating must continue to be made
to the American public. A typical US diet – including, for
example, eggs and bacon for breakfast, a hamburger and glass of
milk for lunch, and a meat dish for dinner – can supply more
than 200 grams of protein a day, or about four times the highest
recommended intake. These eating habits carry serious consequences
for the health of individuals and the ability of countries to feed
the greatest number of people from the available food-production
This article will present some of the key arguments in favor of
a vegetarian diet, giving health-care providers the information
to help their patients (and themselves) make healthful dietary choices.
Myths about Protein
Protein is one of the most misunderstood areas of nutrition, resulting
in myths about the function of protein in the body, the dietary
sources of this nutrient, and the potential consequences of consuming
too little protein. These myths may be so entrenched in our collective
psyche that we find it difficult to let them go, even though scientific
research shows them to be false.
What follows are some of the common misconceptions about protein:
Are Our Only Source of Complete Protein
The American Dietetic Association and Dietitians of Canada report
in a position paper that they have reviewed the scientific data
concerning key nutrients for vegetarians and concluded that a vegetarian
diet can meet recommendations for all of those nutrients, including
protein. The two groups state that "appropriately planned
vegetarian diets are healthful, nutritionally adequate, and provide
health benefits in the prevention and treatment of certain diseases."1
A Vegetarian Diet
Will Make You Protein-Deficient and Sick
Scientific literature in the US has revealed what other cultures,
such as the Hindu and the Japanese, have known for thousands of
years: We do not need meat or dairy products to sustain human life
and health. The healthiest civilizations are those that consume
little or no meat and lead essentially vegetarian lifestyles. There
is some evidence that people who eat primarily plant-based diets
have longer, relatively healthier lives than do we in the West.
Plant consumption has demonstrated a prophylactic effect against
various illnesses associated with lifestyle.
In contrast, meat-eaters may be prone to illnesses of the digestive
and excretory systems and disorders resulting from generalized swelling
and histamine response. The saturated fats in meat have been linked
to breast and colon cancer and cardiovascular disorders.
It is Impossible
to Consume Too Much Protein, Because Any Excess Will Be Stored in
Protein is not stored in muscles, and excessive intake can be harmful.
One potential problem is kidney damage. Excess protein causes excess
urea, a byproduct of protein metabolism. The kidneys must work overtime
to filter urea if it builds up in the bloodstream, and the stress
can lead to kidney damage. This problem is especially serious for
older people, whose kidneys function less efficiently, and people
with preexisting kidney damage.
Other potential effects of an excessive protein intake include:
(1) dehydration, which may result when one's water consumption is
not sufficient for the kidneys to filter urea out of the bloodstream;
(2) a buildup of ammonia, another nitrogen byproduct of protein
metabolism, in the intestinal tract2; and (3) calcium deficiency,
which may occur even when we consume ample calcium-rich milk. Milk
is difficult to digest, and much of its calcium never gets into
the bloodstream. Milk is also high in phosphorus, which binds to
calcium and makes it less absorbable. Much of this calcium is then
excreted in the urine.
Is Low in Calories, While Carbohydrates Are Fattening
Animal protein is in fact extremely high in calories because it
usually contains a lot of fat. An average 16-ounce steak, for example,
has about 1,500 calories. There is little doubt that excess meat
consumption is one of the major causes of obesity in the US.
Humans Were Made to Eat Meat
Physiologically, we are vegetarians. Carnivorous animals have very
short intestinal tracts so that meat remains in the body for only
a short time. Humans, by contrast, have long digestive tracts. Some
portion of ingested meat may stay in the body for three to four
days, during which it begins to decompose and putrefy at our 98.6°
body temperature. This putrefaction may be one of the major causes
of colon and prostate problems.
There is no question that protein is an essential nutrient. It helps
to build, maintain, and repair just about every part of the body.
It makes up our hair, fingernails and toenails, muscles, cartilage,
and tendons, along with many hormones, antibodies, and enzymes.
Chemically, proteins are long-chain molecules made up of amino acids.
There are approximately 22 of them in the protein we use. These
same amino acids make up all protein in nature, be it plant, animal,
or human. There are eight amino acids that the adult body cannot
manufacture: valine, leucine, isoleucine, lysine, threonine, tryptophan,
methionine, and phenylalanine. These essential amino acids must
therefore be obtained from the diet. For children, histidine also
is an essential amino acid; it is important for growth and development.
Because protein is so critical, we must ensure that we consume sufficient
quantities. Otherwise, the body will break down more molecules than
it can build up, resulting in overall deterioration. Pregnant women
must be especially careful to avoid such a situation, as it will
affect both their health and their unborn babies' as well.
How much protein is enough? Ideally, the most precise way to determine
a person's protein needs would be to measure his or her nitrogen
input versus nitrogen output in a given day. Protein is the only
nutrient that supplies the body with nitrogen, and an adequate intake
from the foods we eat creates a "nitrogen balance." We
will have a "negative nitrogen balance" if our output
of nitrogen exceeds our dietary intake.
Experiments have shown that people can maintain proper nitrogen
equilibrium when consuming only plant sources of protein.3
It is not scientifically proven that we must eat any animal foods
to obtain our daily nitrogen requirements. Eating a variety of legumes,
grains, vegetables, nuts, and seeds will provide adequate amounts
of high-quality protein, even from the point of view of nitrogen
While nitrogen utilization may be an ideal way to determine one's
protein requirements, this method is not practicable on a large-scale
or regular basis. Therefore, we must turn to established tables
that "guesstimate" required protein levels. Almost all
of the statistics in this area are inflated with a safety margin
to one degree or another.
The World Health Organization (WHO) and Food and Agriculture Organization
(FAO) recently published a technical report on protein and amino
acid requirements. This analysis finds that the safe level of protein
intake for adults is 0.83 grams per kilogram (kg) of body weight
per day – a level that "would be expected to meet the
requirements of most (97.5%) of the healthy adult population."
The safe levels of protein intake per kg of body weight are higher
for children, while women who are pregnant or lactating require
extra protein as well.4
A similar recommendation for protein intake in adults – 0.8
grams of good-quality protein per kg of body weight – comes
from the Institute of Medicine, part of the National Academy of
Sciences.5 By this method, you multiply your body weight
in pounds by 0.453 (to convert to kilograms), then multiply by 0.8.
If you weigh 155 pounds, for example, you multiply that figure by
0.453, which is 70.2 kg, then multiply by 0.8 grams per kg to arrive
at 56 grams of protein per day.
The Institute of Medicine's 2005 recommended
dietary allowances (RDAs) for protein are as follows6:
Children (boys and girls)
Boys, 14-18 years
Girls, 14-18 years
Men, 19 years and older
Women, 19 years and older
All age groups
All age groups
RDA For Protein
"Adequate Intake"1.52 g/kg/d based on human milk
1.2 g/kg/d or 11 g/d
1.05 g/kg/d or 13 g/d
0.95 g/kg/d or 19 g/d
0.95 g/kg/d or 34 g/d
0.85 g/kg/d or 52 g/d
0.85 g/kg/d or 46 g/d
0.80 g/kg/d or 56 g/d
0.80 g/kg/d or 46 g/d
1.1 g/kg/d of protein, or
+25 g/d of additional protein
1.3 g/kg/d of protein, or
+25 g/d of additional protein
The figures on protein requirements
illustrate that we really need very little protein, which is easily
available from nonanimal sources.
A Focus on Protein
The popularity of meat and other animal proteins in the US diet
can be traced to the early 1940s, when the concept of "complete"
and "incomplete" proteins was popularized. Many of us
were taught that meat, eggs, and dairy products were complete proteins.
The other foods – legumes, grains, nuts, vegetables, fruits
– were incomplete sources. According to the original theory,
complete proteins had all of the essential amino acids in the right
proportions to be used by the body, while incomplete proteins lacked
certain amino acids and did not have them in the right proportions.
There was little recognition of the significant protein contributions
of the plant foods.
What is amazing about this theory is that it remained intact for
so long, when in fact it is wholly unfounded. Plant proteins contain
all of the essential amino acids, although particular ones (such
as lysine, sulfur-containing amino acids, and threonine) may be
lower in plant foods than in animal foods. Despite these differences,
the essential amino acids needed to meet the body's requirements
and maintain nitrogen balance can come from both plant and animal
sources: meat, fish, dairy, eggs, legumes, nuts and seeds, grains,
vegetables, and combinations of these foods.
This information on protein is available to consumers from organizations
such as the American Heart Association (AHA). It advises that soy
protein is equal to animal proteins (making it suitable as a sole
source of protein), and that whole grains, legumes, vegetables,
seeds, and nuts contain both essential and nonessential amino acids.
The AHA states: "You don't need to eat foods from animals to
have enough protein in your diet. Plant proteins alone can provide
enough of the essential and nonessential amino acids, as long as
sources of dietary protein are varied and caloric intake is high
enough to meet energy needs."7
Protein foods must be evaluated in terms of their quality. In a
2007 report on protein and amino acid requirements, WHO and FAO
explain that the purpose of evaluating protein quality is to determine
"the capacity of food protein sources and diets to satisfy
the metabolic demand for amino acids and nitrogen. Thus any measure
of the overall quality of dietary protein, if correctly determined,
should predict the overall efficiency of protein utilization."
On this topic, the report states that "protein utilization
is generally discussed in terms of digestibility, a measure of the
dietary intake which is made available to the organism after digestion
and absorption, and biological value, a measure of how well the
absorbed amino acid profile matches that of the requirement. Overall
protein utilization, i.e. net protein utilization (NPU), will therefore
reflect both digestibility and biological value."8
Interestingly, when nitrogen balance studies involve fast-growing
young children, differences in digestibility, biological value,
and NPU between protein sources are clear and predictable, says
WHO/FAO. Values range "from near-perfect utilization …
for animal proteins, to much lower values for some plant-based diets."
In contrast, studies of adults are difficult to interpret, with
outcomes differing from predictable values. In a 2003 meta-analysis
of nitrogen balance studies, explains WHO/FAO, the median protein
requirement (0.66 g/kg per day) more than doubled the obligatory
nitrogen losses (˜0.3 g/kg per day) because the slope, which
indicates the efficiency of protein utilization, was <0.5. "Furthermore,
there was no significant influence of variation in the protein sources
(animal, vegetable, or mixed protein) on the slope and consequent
requirement. This implies that for human adults, net protein utilization
values for diets of most sources are similar, but much lower than
would be predicted," states WHO/FAO. It also indicates that
we must gain a "better understanding of how the organism adapts
to variation in protein intake."9
The internationally accepted method of protein quality assessment
is the protein digestibility-corrected amino acid score (PDCAAS),
which has been adopted by WHO for measuring the protein value of
foods and by the US Food and Drug Administration for calculating
protein for food labels. The PDCAAS is used to assess the quality
of both individual sources of protein and food mixtures. In the
early 1990s, it replaced the long-used protein efficiency ratio
(PER), a rat growth assay method of assessing food proteins. According
to an FAO official, because rats grow faster than humans (increasing
the rat's essential amino acid requirements), PER overestimated
the value of some animal proteins for human growth and underestimated
the value of some vegetable proteins.10
The PDCAAS method evaluates the quality of protein foods based on
two factors: digestibility and amino acid composition. As described
by Millward et al., the amount of potentially "limiting"
amino acids in a given protein food or protein combination is compared
with their respective content in the reference pattern used by PDCAAS.
(The reference pattern represents the essential amino acid requirements
of a 2- to 5-year-old child.) This comparison identifies the single
most limiting amino acid, which determines the amino acid score.
"The current consensus is that meeting the minimum requirements
for lysine, methionine, and tryptophan, the most limiting amino
acids in poor quality proteins, determines the amino acid score
and will lead to a plateau of nitrogen retention," state the
authors. The amino acid score is corrected for digestibility to
arrive at the test protein's PDCAAS value.11
The highest PDCAAS value given to a food is 100% (1.00). If the
value of a food exceeds 100%, the score is truncated to 1.00 on
the grounds that the nutritional benefit of a protein is not increased
by essential amino acid content in excess of the reference pattern.12
Egg white and casein have a PDCAAS of 1.00. Soybean isolate scores
0.99, and beef protein is 0.92. Examples of plant protein values
include: pea flour, 0.69; kidney beans, 0.68; lentils, 0.52; and
whole wheat, 0.40.13
One criticism of the PDCAAS method concerns mixed diets containing
proteins from a number of sources. As explained by Schaafsma, the
truncation of PDCAAS values to 100% makes sense only in cases where
the diet consists of a sole source of protein (such as infant feeding
or enteral feeding). In all other diets, where the sources of protein
are mixed, the truncated values largely eliminate "differences
in the power of high-quality proteins to balance the amino acid
composition of inferior proteins," says Schaafsma. He offers
the example of 1 gram of wheat protein (which is low in lysine).
It may be balanced by 1.2 grams of casein versus 6.2 grams of soy
protein. This concept is highly relevant for plant protein sources
containing low concentrations of lysine, sulfur-containing amino
acids, and threonine. The author concludes: "For evaluation
of the nutritional significance of proteins as part of mixed diets,
the truncated value should not be used. In those cases, a more detailed
evaluation of the contribution of the protein to the amino acid
composition of the mixed diet is required."14
With plants accounting for 65% of the protein supply worldwide,
the concept of protein complementation warrants consideration. In
the American Journal of Clinical Nutrition,
Young and Pellett explain that some plant foods may not be adequate
as sole sources of protein, especially for infants and children,
due to their low concentration of protein or quality of protein.
However, children can thrive and recover from severe malnutrition
when eating well-formulated diets based on plant foods alone. They
state: "Thus, plant foods in appropriate amounts and combinations
are able to supply the essential nutrients required for maintenance
of adequate health and nutrition."15
The authors underscore the potentially high nutritional quality
of plant protein mixtures. As an example, they note that the soybean
is low in sulfur-containing amino acids and high in lysine, while
foods such as cereal grains and sesame flour are low mainly in lysine.
Therefore, the combination of soy protein with a cereal that contains
a relatively good concentration of s-amino acids will result in
a complementary effect – that is, the protein quality of the
mixture exceeds that of either food alone. This synergistic effect
occurs when "one of the protein sources has a considerably
higher concentration of the most limiting amino acid in the other
According to a meta-analysis of nitrogen balance studies, the research
shows that "well-processed soy proteins were equivalent to
animal protein, whereas wheat proteins were used with lower efficiency
than were animal protein (beef)." Similarly, studies comparing
egg proteins with rice or wheat gluten also found significant differences
in utilization between the animal and plant sources of protein.
However, the authors state that "whereas lysine is likely to
be the most limiting of the indispensable amino acids in diets based
predominantly on cereal proteins, especially wheat, the risk of
lysine inadequacy is substantially reduced by the inclusion of relatively
modest amounts of animal or vegetable proteins, such as those from
legumes and oil seeds or, where appropriate, through lysine fortification
of cereal flour."17
Young and Pellett conclude that plant protein mixtures "can
serve as a complete and well-balanced source of amino acids. …
Consumers do not need to be at all concerned about amino acid imbalances
when the dietary amino acid supply is from the plant-food proteins
that make up our usual diets. Mixtures of plant proteins can be
fully adequate for meeting human requirements. From the standpoint
of the composition of a healthful diet, they serve as a desirable
vehicle for carrying nitrogen and indispensable amino acids to meet
both our needs and wants."18
Experts on vegetarian eating advise that it is not necessary to
combine complementary plant proteins at the same meal. The important
point is to eat a varied diet each day of legumes, grains, nuts,
seeds, and vegetables. According to the American Dietetic Association,
"Research indicates that an assortment of plant foods eaten
over the course of a day can provide all essential amino acids and
ensure adequate nitrogen retention and use in healthy adults, thus
complementary proteins do not need to be consumed at the same meal."
Young and Pellett believe "that for usual conditions of healthy
living it is not necessary to consume complementary proteins at
the same time and that separation of the proteins among meals over
the course of a day would still permit the nutritional benefits
of complementation."20 In a letter to Circulation,
John A. McDougall, a leading nutritional physician, states: "A
careful look at the founding scientific research and some simple
math prove it is impossible to design an amino acid-deficient diet
based on the amounts of unprocessed starches and vegetables sufficient
to meet the calorie needs of humans. Furthermore, mixing foods to
make a complementary amino acid composition is unnecessary."21
Organizations such as the Vegan Society, the Vegetarian Resource
Group, and Vegan Outreach also inform consumers that it is not necessary
to combine proteins at each meal.
Egg Protein Index
For vegetarians who want to consume optimal food mixtures, it is
useful to understand which combinations can be used most efficiently
by the body. We, the authors of this article, working with mathematician
Hillard Fitzkee, analyzed by computer the amino acid structure of
major animal and plant foods and evaluated the quality of many combinations
of plant proteins. These plant foods can be combined in normal serving
sizes to obtain all of the amino acids – and therefore protein
– one needs.
We created a rating system called the egg protein index (EPI) from
our research. This rating assigns a score to each food – or
combination of foods – based on how closely the essential
amino acids they contain match the percentage contributions of the
egg, which we selected as our standard. The egg contains the eight
essential amino acids in the proportions most efficient for human
protein metabolism, and has an NPU value of 94 on a scale of 100.
It should be noted that while the egg was selected as the ideal
food with which to compare others, another food could have been
chosen. Our definition of quality is not a function of egg protein
Within this unbiased rating system, a food or food combination is
most beneficial if each of its essential amino acids is present
in the same percentage contribution as that of the egg. If the essential
protein structure of the food(s) were to match that of the egg exactly,
then the EPI would be zero. The poorer the match for a food or food
combination, the higher the EPI number it receives.
As an example, the EPI of rice alone is 31.14. This compares with
16.81 for whole milk. However, one could add a "balancing"
portion of selected amino acids to make the rice identical to the
egg. This would require 448 milligrams of seven of the eight essential
amino acids per 100 grams of rice. But this type of precision is
not needed to obtain desirable results. Only 180 milligrams of four
of the essential amino acids obtained from a complementary food
could improve rice's EPI from 31.14 to 4.52. Thus, we can increase
the quality of rice by improving the essential protein portion;
we do not need to produce more protein in the 100 grams of rice
or optimize all of its protein.
Here are some examples of EPIs for combinations
of two foods:
This assessment of food combinations goes beyond the "limiting
amino acid" approach, in which people would combine one food
with another based on which amino acid it contained in the smallest
amount. The problem was that as they tried to eat enough of a particular
food to obtain the minimum requirement of one amino acid, they would
overconsume other amino acids. Our computations took into account
not merely the one or two amino acids in shortest supply in each
food, but all eight essential amino acids and the extent to which
their proportions vary from those of the egg. As a result, vegetarians
can obtain higher-quality and more usable protein, avoid excess
consumption of protein or particular amino acids, and consume fewer
total calories for better weight control.
Based on our research, the two-food combinations with the highest
quality of protein are:
1. Hijiki Seaweed/Amaranth
2. Triticale Flour/Amaranth
3. Basmati (Long-Grain, Parboiled)/Amaranth
4. Sunflower Flour/Amaranth
5. Pine Nuts/Swiss Chard (Raw)
6. Sunflower Flour/Green Pea (Dry)
7. Sunflower (Hulled)/Amaranth
8. Whole Wheat Flour/Amaranth
9. Sesame Seed (Meal)/Amaranth
10. Spinach (Raw)/Pine Nuts
11. Buckwheat Flour (Dark)/Basmati (Long-Grain Parboiled)
12. Walnut, Persian/Amaranth
13. Pine Nuts/Amaranth
15. Brown Rice (Raw, Short-Grain)/Amaranth
16. Sunflower (Hulled)/Pine Nuts
18. Watermelon Seed/Amaranth
19. Filbert (Shelled)/Amaranth
20. Pine Nuts/Broccoli (Cooked)
A Closer Look at Meat
Despite the ability of plant foods to meet our amino acid requirements,
the diet of many Americans still pivots around meat. They believe
that it is synonymous with protein, health, and strength; and their
diet typically includes meat and dairy products at most meals.
Major associations like the American Heart Association and the American
Cancer Society have warned that this type of meat consumption is
not in our best interest. But after decades of hearing otherwise,
people may find this hard to believe.
So what is the truth about meat?
First, it is true that meat supplies protein, but not in the quantities
or of the quality that most people think. Beef, for example, is
20% protein; the rest is fat and water. In addition, beef is one
of the highest-calorie foods available, due to it high fat content.
As mentioned, an average 16-ounce steak has about 1,500 calories.
If this were eaten with a baked potato with butter and sour cream
and a dessert, the calorie count would be 2,500. Furthermore, the
fat in beef is saturated. This builds up in arteries as cholesterol
and is thought to be one of the major culprits in arteriosclerosis
and heart disease.
In addition, meat is one of the most chemical-ridden foods in the
US diet. Five major classes of drugs are administered to food animals,
according to the National Research Council. They are: (1) topical
antiseptics, bactericides, and fungicides; (2) ionophores (these
drugs alter stomach microorganisms); (3) hormone and hormonelike
production enhancers; (4) antiparasite drugs; and (5) antibiotics
to control disease and promote growth.25 It is known
that some of these drugs may be transferred to the human population
via meat, dairy, and egg products.
Antibiotics are perhaps the most widely used (and abused) of these
drugs. They are given in subtherapeutic doses to promote the growth
of food animals. They also are used to prevent diseases that would
otherwise be rampant in the close, unsanitary conditions in which
animals are raised. In 1954, 490,000 pounds of antibiotics were
used in livestock production. Today the figure is 25 million pounds.26
As reported by the Sierra Club: "The routine, medically unnecessary
use of antibiotics to promote the enhanced growth of livestock is
making disease-causing bacteria more resistant to the drugs, which
diminishes their power to treat life-threatening diseases in humans."27
In addition to antibiotics, hormones are routinely used with beef
cattle to regulate breeding, tranquilize, and promote weight gain.
These synthetic hormones can cause cancer in the animals, which
in most cases does not affect the marketability of the meat. We
do not yet know the degree to which cancer is viral in its origins,
but studies have found viruses to be responsible for some cancers.28
So, apart from being unappetizing, cancerous meat may actually be
the vehicle for cancer viruses to enter our bodies. Additionally,
the residues of estrogen, one of the hormones commonly fed to these
animals, may increase women's chances of contracting uterine and
breast cancer. Children exposed to estrogen may enter puberty prematurely.
DES (diethylstilbestrol), a hormone that was banned from human use
in the 1960s, remained in use on animals until 1979.
Other drugs used with animals are Ralgro, an estrogenlike compound;
Synovex, a naturally occurring hormone that affects weight gain;
and Lutalyse, a prostaglandin, which is often given to an entire
herd so that they will ovulate at the same time. This drug can affect
the menstrual cycles of women and cause pregnant women to miscarry.
In addition, cattle are sprayed with pesticides such as Vapona,
which is in the same family as nerve gas.
Unfortunately, meat is not the only animal product filled with chemicals.
Chemicals fed to or sprayed on milk cows are passed into their milk.
Although federal law prohibits the use of hormones, in particular,
in poultry or hogs, chickens receive other drugs that show up in
their eggs or meat.29 Chickens are given additional drugs
to promote the hardness of eggshells and uniformity of yolks.
The Choice Is Yours
There is no question that we require protein. But the source of
that protein is a matter of personal choice and responsibility.
Red meat and other animal foods have received top billing in the
American diet, but many people are beginning to assess the alternatives
as they become more aware of the disadvantages associated with red
meat and animal products in general.
Coming in Part Two: The Ecological Mandate For
Gary Null has authored more than 75 books on health and nutrition,
and numerous articles published in research journals. He is an adjunct
professor in graduate studies, Public Health Curriculum, at Fairleigh
Dickinson University in Teaneck, New Jersey. Null holds a PhD in
human nutrition and public health science from the Union Graduate
Martin Feldman, MD, practices complementary medicine. He is an
assistant clinical professor of neurology at the Mount Sinai School
of Medicine in New York City.
Gary Null, PhD
New York, New York 10024 USA
Martin Feldman, MD
132 East 76th Street
New York, New York 10021 USA
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Accessed Nov. 1, 2008.
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