Nutrition & Health   > Protein and a Health-Supporting Diet


John McDougall, M.D. (From New York Times Best Seller "The McDougall Plan")


  • Are Americans among the most malnourished people in the world?

  • Are the meat and dairy industries brainwashing us?

  • Is the medical profession ignorant about our nutritional needs?

  • Has our government given us faulty information on proper diets?

Yes is the answer to all of the above...


Proteins provide important materials to build and maintain our hormones, enzymes, muscles, and many other body tissues. Accurate estimates of human adult protein needs determined by careful studies show that as little as 2.5 percent of our daily calorie intake can be safely provided in the form of protein. This amount is equivalent to a little less than 20 grams -- two thirds of an ounce -- for an adult man. The World Health Organization (WHO) has established a higher minimum daily requirement for protein to be approximately 5 percent of the daily intake, but many populations have lived in excellent health on less than this amount. (Protein requirements for pregnancy set by the WHO are 6 percent, and for lactation 6.7 percent of the daily calorie intake.)


An average working man consumes 3,000 calories a day, so 5 percent of the total would be 150 calories from protein. Since each gram of protein is equal to 4 calories, this would represent 37 grams of protein. An average woman consuming 2,300 calories a day needs 29 grams of protein. These minimum requirements provide for a large margin of safety that easily covers people who theoretically could have greater protein needs. This quantity of protein is almost impossible to avoid if enough food is consumed to meet daily calorie needs. For example, 3,000 calories of rice alone would provide 60 grams of highly usable protein.


The building blocks of protein are called amino acids. Varied combinations among twenty amino acids form the proteins found in all kinds of living creatures. All sources of unprocessed foods, including meat, dairy, fish, shellfish, plants, and microorganisms contain all twenty of these amino acids. However, the amount of each amino acid that is present varies among different foods. Plants make all of them from carbon, nitrogen, sulfur, and water. Animals, including humans, can synthesize some of the needed amino acids, but others must be obtained from their food. The amino acids that cannot be synthesized and which must be provided by the diet are known as essential amino acids.


Protein Studies on Rats


Many people believe that animal foods contain protein that is superior in quality to the protein found in plants. This is a misconception dating back to 1914, when Osborn and Mendel studied the protein requirements of laboratory rats. They found that rats grew better on animal sources of protein than on vegetable sources. Investigators at that time suspected that the vegetable foods had insufficient amounts of some of the amino acids essential for the normal growth of rats. Because of these and other animal-based experiments, flesh, eggs and dairy products were classified as superior or "Class A" protein sources. Vegetable proteins were designated inferior or "Class B" proteins.


Studies in the mid-1940s found that ten amino acids were essential for a rat's diet. If the level of anyone amino acid was low, the rats could not efficiently utilize the protein and failed to grow normally. Animal products, such as meat, poultry, milk, and eggs, were found to contain these ten essential amino acids in just the right proportions for rats.


Based on these early rat experiments the amino acid pattern found in animal products was declared to be standard by which to compare amino acid pattern of vegetable foods. According to this concept, wheat and rice were declared deficient in lysine, and corn was deficient in tryptophan. It has since been shown that the initial premise that animal products supplied the most ideal protein pattern for humans, as it did for rats, was incorrect. Therefore, the idea that vegetable foods were deficient in certain amino acids for our needs was inappropriately based on a standard diet ideal for rats. At that early time no one knew the actual protein or amino acid requirements for humans.


In 1952 William Rose completed a long series of experiments to determine the amino acid requirements for human males. He fed his subjects a synthetic mixture of corn (maize) starch, sucrose, butter fat, vitamins, and highly purified amino acids, and then gradually eliminated one amino acid at a time.


The study used a chemical measurement called nitrogen balance to determine whether the subjects were getting enough usable protein from the mixture. When an essential amino acid was given in insufficient amounts for approximately two days, all subjects complained of similar symptoms: a clear increase in nervous irritability, extreme fatigue, and a profound failure of appetite. The subjects were unable to continue the amino-acid-deficient diets for more than a few days at a time. From his experiments Dr. Rose found that only eight of the ten amino acids essential to rats were also essential to people. Arginine and histidine, the two other amino acids that were found essential in the rat's diet, were not essential to human adults. (However, histidine is essential in diets of young children, and aginine is made slowly by infants. Plants are excellent sources of both of these amino acids and easily satisfy these amino acid needs of growing young children.)


Through these studies, Rose determined a minimum level of intake for each of the essential amino acids. He found small amounts of variation in individual needs among his subjects, but these differences did not seem to correlate with their weight or metabolic rate. Because of these unexplained differences among people, he included a large margin of safety in his final conclusion on minimum amino acid requirements. For each amino acid he took the highest recorded level of need in any single subject as his minimum requirement, and then doubled that amount for a recommended requirement described as "a definitely safe intake." It is important to realize that even his higher requirement is easily met by a health-supporting diet centered around any single starch. In all but very young children, as long as energy needs are satisfied by unprocessed starches, protein needs are automatically satisfied in almost every situation because of the basic and complete design of the food. Infants less than two years of age have difficulty consuming enough vegetable foods to meet their calorie needs because of the immaturity of their digestive systems and the bulky nature of some starches. Therefore, as commonly practiced before modernization of societies, infants should obtain at least 25 to 50 percent of their diet from breast milk (or the best milk substitute available).


The results of Rose's study are summarized below, under "minimum requirements." From the chart, is it clear that even single vegetable foods contain more than enough of all amino acids essential for humans.



Rose's Rose's Beef

(Grams per day) Minimum Recom. Brown Oatmeal Wheat White Broccoli club

AMINO ACIDS Require. Require. Corn rice flakes flour beans Asparagus Tomatoes steaks Egg Milk

Tryptophan 0.25 0.50 0.66 0.71 1.40 1.80 1.80 3.90 3.80 1.40 3.10 3.80 2.30
Phenylalanine 0.28 0.56 6.13 3.10 5.80 5.90 10.90 10.20 12.20 4.30 11.20 13.90 7.70
Leucine 1.10 2.20 12.0 5.50 8.10 8.00 17.0 14.60 16.50 6.10 22.40 21.00 15.90
Isoleucine 0.70 1.40 4.10 3.00 5.60 5.20 11.30 11.90 12.80 4.40 14.30 15.70 10.30
Lysine 0.80 1.60 4.10 2.50 4.00 3.20 14.70 15.50 14.80 6.30 23.90 15.3.0 12.50
Valine 0.80 1.60 6.80 4.50 6.40 5.50 12.10 16.00 17.30 4.20 15.10 17.70 11.70
Methionine 0.11 0.22 2.10 1.10 1.60 1.80 2.00 5.00 5.10 1.10 6.80 7.40 3.90
Threonine 0.50 1.00 4.50 2.50 3.60 3.50 8.50 9.90 12.50 4.90 12.10 12.00 7.40
Total Protein 20.00 37.00 109.00 64.00 108.00 120.00 198.00 330.00 338.00 150.00 276.00 238.00 160.00




Many investigators have measured the capacity of plant foods to satisfy protein needs. Their findings show that children and adults thrive on diets based on single or combined starches, and grow healthy and strong. Furthermore, many investigators have found no improvement by mixing plant foods or supplementing them with amino acid mixtures to make the combined amino acid pattern look more like that of flesh, milk, or eggs. In fact, supplementing a food with an amino acid in order to conform to a contrived reference standard can create amino acid imbalances. For example, young children fed diets based on wheat or corn and supplemented with the amino acids tryptophan and methionine in order to conform to the standard requirements set by the Food and Agriculture Organization of the United Nations (FAO) developed negative responses in terms of nitrogen balance (the body's utilization of protein.)


Many books popular among vegetarians today place great emphasis on combining vegetable foods to create an amino acid pattern that resembles that found in animal foods. This emphasis is unnecessary and implies that it is difficult to obtain complete sources for synthesizing proteins from vegetables without detailed nutritional knowledge. Because of this complicated and incorrect idea, people are frightened away from vegetable-based diets. Nature has designed vegetable foods to be complete. If people living before the age of modern dietics had had to worry about achieving the correct protein combinations in their diets, our species would not have survived for these millions of years. Humans have related to the world of food with primarily one drive -- hunger -- and in response to this one basic drive our needs for calories, proteins, amino acids, essential fat, fibre, vitamins and minerals have been satisfied. In fact, one who follows the advice for protein combining can unintentionally design a diet containing an excessive and therefore harmful amount of protein by including too many high-protein legumes.


As the many amino acid studies have shown, the foods that provide correct nutrition for rats are not necessarily the same for humans. The diet of a rat is considerably different from that of a human. Based on weight, the adult rat requires three and a half times as much protein as a human, and the individual amino acids required are considerably different. Because a rat grows rapidly into adult size compared with a person, the rat's requirements for protein are much higher. This difference in need is especially clear when the breast milk of the two spices is compared. The protein of rat breast milk is ten times more concentrated than that of the milk intended for human babies.


The pictures one often sees of "protein-deficient" children in areas of famine in Asia or Africa are actually pictures of starvation, which is more accurately described as calorie deficiency. When these children come under medical supervision, they are nourished back to health with their local diets of corn, wheat, rice, and/or beans. Children recovering from starvation grow up to eighteen times faster than usual and require a higher protein content to provide for their catch-up in development. This exaggerated protein need can be met by a variety of starchy foods.


Calcium Loss Caused by Excess Proteins


Eating excessive amounts of proteins can seriously damage our health. When our diet contains more proteins than we need, the excess is broken down in the liver and excreted through the kidneys as urea. This protein breakdown product is called BUN, or blood urea nitrogen. Urea has a diuretic action, which caused the kidneys to work harder and excrete more water. Along with water, minerals are lost in the urine, and one of the most important minerals lost in this manner is calcium.


On the average, Americans take in a little more than 100 grams of protein and 800 milligrams of calcium daily. In general, studies have shown that young men consuming diets containing more than 95 grams of protein daily developed a negative calcium balance, even with very high calcium intakes. However, in one long-term study, investigators measured calcium balance in adults and found that when subjects consumed as little as 75 grams of protein a day, even with daily intakes as high as 1400 milligrams of calcium, more calcium was lost in urine then was absorbed into the body from the diet (a negative calcium balance). This would mean that most westerners have a net loss of calcium from their bodies every day. The deficit must be made up from the body stores of calcium, which are primarily the bones. The end result of this continuous process is calcium-deficient bones that break with the slightest provocation, such as a sneeze that can crack a rib or a normal step that can break a hip. This condition is called osteoporosis, and in affluent societies it occurs in about 25 percent of women over the age of sixty-five. By the time of diagnosis, 50 to 75 percent of the original bone material has been lost from the skeleton. Observations of various populations worldwide show that the higher the protein intake, the more common is osteoporosis. Bantus living in Africa on low-protein vegetable diets, consuming 47 grams of protein and 400 milligrams of calcium, are essentially free of osteoporosis. Genetic relatives of Bantu, a population of blacks investigated in the United States, consume a rich diet with plenty of meat and dairy foods, yet have osteoporosis nearly as commonly as do whites. An excellent example of the effects of excess protein is seen in native Eskimos who consume a diet very high in protein -- 250 to 400 grams a day from fish, walrus, and whale, along with a high calcium intake of more than 2,000 milligrams from fishbones. Yet these very physically active people have one of the highest rates of osteoporosis in the world.


The effect of protein on calcium metabolism suggests a benefit from a low-protein diet in the treatment of osteoporosis, because lowering the protein content of the diet is the most effective means of restoring a positive calcium balance. So it would follow that one of the measures of preventing this condition should also include a low-protein diet. Other factors are also involved in this condition, including physical activity and hormone status.


Kidney Damage


The calcium lost in high-protein diets ends up in the urine and results in high levels of calcium in the kidney system. This contributes to the formation of painful calcium kidney stones. Calcium stones are the most common type found in persons in affluent societies. So, a health-supporting diet that emphasizes low-protein foods would also prevent the formation of calcium kidney stones in most people and would be of particular benefit to those who suffer from recurring stones.


For certain individuals, limiting the intake of protein can be essential not only for improving health but for staying alive. Protein consumed in excess of our needs causes destruction of kidney tissue and progressive deterioration of kidney function. By the eighth decade of life, people in affluent societies commonly lose 75 percent of their kidney function. In someone with normal kidneys this loss rarely becomes significant because of the tremendous extra capacity the healthy kidney possesses. However, when a person suffers from an additional disease of the kidney, such as diabetes, surgical loss, or injury from toxic substances, the damage caused by the protein becomes critical. People with partial loss or damage to their kidneys, when placed on a protein-restricted diet, are able to preserve much of their remaining kidney function. Those unfortunate patients left on high-protein diets show progressive deterioration of their kidneys to a point where all too soon most will end up needing help from kidney machines.


The body's capacity to store protein is minimal, at most. Protein consumed in excess of the amount needed for growth and tissue replacement is excreted. The liver and kidneys enlarge from the added work load of protein metabolism. Osteoporosis and kidney stones are common consequences of prolonged consumption of high-protein foods.


Protein is broken down in the liver, and the waste products are excreted through the kidneys. Failure of either these organs to function normally will result in a buildup of protein breakdown products. Accumulation of these products will make a person extremely ill. On a low-protein diet, people with kidney or liver failure improve dramatically. There are other dietary restrictions placed on kidney and liver patients. For example, it is extremely important for the sodium, potassium, and phosphates in the diet to be kept low with most kidney disease. Dietary and medical management of people with these and other serious ailments require the strict supervision of someone trained in this type of care.


High-protein foods are generally high in purines, which are the primary building blocks of our generic code material, DNA and RNA. Purines break down to form uric acid (not urea). The collection of uric acid in the joints leads to gout, a painful and deforming type of arthritis. Uric acid concentrated in the kidney system also leads to formation of uric acid kidney stones in susceptible people. Kidney stones are prevented and gout is easily cured with a low-protein, low-purine diet.


Protein Content in Various Foods


Most animal products are inherently high in protein content. When the fat is removed from a food, the percentage of calories present as protein proportionately increases. For example, when the fat is removed from whole milk to produce skim milk, the relative protein content doubles. Therefore, removing the fat from a food is not without adverse nutritional consequences.


Vegetable products are usually lower in protein content than are animal products. The most important exceptions are the legumes, which include beans, peas, and lentils. These foods can be consumed easily in amounts large enough to yield a diet containing excessive protein. If you are in good health, legumes should be used in no more than one meal per day. The amount should not exceed one cup of cooked legumes per meal. Other high-protein vegetable foods, such as asparagus, lettuce, yeast, and spinach, usually are consumed in such small amounts that they don't have to be consciously limited by healthy people. Those who are placed on severe protein-restricted diets should avoid all high-protein vegetable foods from the table below.


Misunderstandings about calcium and protein by lay persons and professional nutritionists have led to the inclusion of excessive amounts of flesh, dairy foods, and eggs in the western diet. Fortunately, the scientific studies performed during the last half-century clearly demonstrate that a starch-centered diet, with the addition of fruits and vegetables, supplies an excellent protein source and is thereby one of the foundations for excellent nutrition.


Percent of Calories in Selected Foods


Low-protein vegetable foods

apple 1 mangos 4
dates 3 coconuts 5
pineapple 3


Medium-protein vegetable foods

chestnuts 6 corn 12
oranges 8 spaghetti 14
rice 8 oatmeal 15
honeydew melons 10 whole wheat bread 16
almonds 12


High-protein vegetable foods

celery 21 lettuce 34
artichokes 22 asparagus 38
navy beans 26 tofu 44
peas 28 spinach 49
lentils 29 tempeh 49
soybeans 34 yeast 57


Animal Foods

human breast milk 5 milk (skim-0% fat) 41
milk (whole--3.5%) 21 turkey 41
cheddar cheese 25 chicken (light-skinned)76
yogurt 28 cottage cheese 79
milk (low-fat-2%) 28 shrimp 84
hamburger 34 tuna in water 88
mackerel fish 37


The important points to remember are that except for a diet based on low calorie fruits, unprocessed plant foods easily meet protein needs for adults and children, and that excess intake of protein is the real potential for trouble. Protein-depleted starches and simple sugars are sometimes added to the diet of people with kidney and liver disease in order to lower the protein content of the diet even further.


Adapted with kind permission from New York Times Best Seller, "The McDougall Plan," by John A. McDougall, M.D. & Mary A. McDougall, printed by New Win Publishing, Inc. Dr. John A. McDougall graduated from Michigan State University Medical School, received certification from the American Board of Internal Medicine and the National Board of Medical Examiners and is Assistant Clinical Professor at the University of Hawaii School of Medicine. Mary A. McDougall, L.P.N., specializes in nutrition.


Dr. McDougall's Right Foods, is a mission-orientated company that has made great health effortless. The McDougall Program at St. Helena Hospital in the Napa Valley, is a live-in experience, that assures success with the McDougall Program (the professional staff locks you up for 12 days of summer camp). At The McDougall Wellness Clinic, you will feel like the most important person in the world, when you call for help. If you have any questions, or ideas you would like to share, please write or call.


The McDougall Wellness Clinic
PO Box 14039
Santa Rosa, CA 95403
Telephone: (707) 576-1654
FAX: (707) 576-3313
Book orders: (800) 570-1654


Dr. McDougall's Right Foods
101 Utah Avenue
San Francisco, CA
Telephone: (415) 635-6000
FAX: (415) 635-6010
Food Orders: (800) 367-3844


The McDougall Program
St. Helena Hospital
605 Sanitarium Dr.
Deer Park, CA 94576
(707) 963-6365
Reservations: (800) 358-9195


Other Recommended McDougall Books:

The McDougall Quick and Easy Cookbook
The McDougall Program -- Twelve Days to Dynamic Health
The McDougall Program for a Healthy Heart
The McDougall Program for Maximum Weight Loss
The New McDougall Cookbook
McDougall's Medicine -- A Challenging Second Opinion
The McDougall Health-Supporting Cookbooks -- Volumes I & II


Most natural food stores already stock healthy and delicious, low-fat "McDougall's Right Foods." If not, you can ask them to order.


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