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 and others.
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 resources.
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:
Animal Products 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 Muscles
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
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.
Animal Protein 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
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
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 equilibrium.
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
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 Quality
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
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 protein."16
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 in particular.
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
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
Coming in Part Two: The Ecological Mandate For Vegetarian
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
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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Loss. New Jersey: New Century Publishers; 1983.
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Accessed Jan. 12, 2009.
14. Schaafsma, op. cit.
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estimating protein requirements in healthy adults. Am J Clin Nutr. 2003;77:109-127.
18. Young, op. cit.
19. American Dietetic Association, op. cit.
20. Young, op. cit.
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Accessed Dec. 3, 2008.
23. Mangels R. Protein in the vegan diet. Available at: www.vrg.org/nutrition/protein.htm.
Last updated April 26, 2006.
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Last updated Sept. 23, 2008.
25. Board on Agriculture, National Research Council. The Use of Drugs in Food Animals:
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the effectiveness of drugs used to treat disease in humans. Available at: www.sierraclub.org/factoryfarms/factsheets/antibiotics.asp.
Accessed Nov. 1, 2008.
28. American Cancer Society. Infectious agents and cancer. Available at: www.cancer.org/docroot/PED/content/PED_1_3X_Infectious_Agents_and_Cancer.asp.
Last medical review: May 19, 2008.
29. US Department of Agriculture. Food Labeling fact sheet: Meat and poultry labeling
terms. Available at: www.fsis.usda.gov/FactSheets/Meat_&_Poultry_Labeling_Terms/index.asp.
Accessed Aug. 22, 2008.
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