Dr. John & Mary McDougall
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A Brief History of Protein: Passion, Social Bigotry, Rats, and Enlightenment
John McDougall M.D.
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The first trial involved a group of five men connected with Yale University, leading active lives but not engaged in very muscular work. On a low-protein diet (62 grams daily) for 6 months, they all remained healthy and in positive nitrogen balance (more protein went into, than out of, their bodies). The second trial used 13 male volunteers from the Hospital Corps of the U.S. army. They were described as doing moderate work with one day of vigorous activity at the gymnasium. They remained in good health on 61 grams of protein daily. His final trial was with 8 Yale student athletes, some of them with exceptional records of athletic events. They ate an average of 64 grams of protein daily while maintaining their athletic endeavors, and improving their performance by a striking 35 percent. Following these studies, Chittenden in 1904 concluded that 35-50 g of protein a day was adequate for adults, and individuals could maintain their health and fitness on this amount. Studies over the past century have consistently confirmed Professor Chittenden's findings, yet you would hardly know it with the present day popularity of high protein diets.
Rats Confuse Nutritionists
Many people have the idea that animal foods contain protein which is superior in quality to the protein found in plants. This misconception dates back to l9l4, when Lafayette B. Mendel and Thomas B. Osborne studied the protein requirements of laboratory rats and demonstrated nutritional requirements for the individual amino acids.5 They found that rats grew better on animal sources of protein than on vegetable sources. So, 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 foods were classified as superior, or "Class A" protein sources. Vegetable proteins were designated inferior, or "Class B" proteins.
Studies completed in the early 1940's by Dr. William Rose of the University of Illinois found that l0 amino acids were essential for a rat's diet.6 The removal of any one of these essential amino acids from the food of growing rats led to profound nutritive failure, accompanied by a rapid decline in weight, loss of appetite, and eventually death. Animal products, such as meat, poultry, milk, and eggs prevented this decline in the rats' health, and were found to contain the l0 essential amino acids in just the right proportions for needs of growing rats. Based on these early rat experiments the amino acid pattern found in animal products was declared to be the "gold standard" by which to compare the amino acid pattern of vegetable foods. According to this concept, wheat and rice were declared deficient in lysine and corn was deficient in tryptophan.
Subsequent research has shown the obvious: the initial premise, that animal products supply the most ideal protein pattern for humans, as they do for rats, is incorrect.7 The dietary needs of rats are considerably different from those of humans, mainly because rats grow very rapidly into adult size as compared to people. Rats are fully adult after 6 months; whereas a person takes 17 years to fully mature. This difference in need is especially clear when the breast milk of both species is examined and compared. The protein content of rat breast milk is 10 times greater than the milk intended for human babies.8,9 Baby rats double in size in 4.5 days; an infant doubles in size in 6 months. The obvious reason for the different needs is because rats grow very rapidly into adult size as compared to humans; therefore requirements for protein to support that growth are very much higher.
Dr. William Rose Discovers Human Needs
In 1942, Dr. William Rose turned his attention from rats to people and began studying the amino acid requirements for humans using basically the same methodology he had used with rats. Healthy, male graduate students, grateful in those days for the free food, the dollar a day they were paid and the prospect of getting their initials in print in Rose's widely read publications, served as his experimental animals. They were fed a diet consisting of corn starch, sucrose, butter fat without protein, corn oil, inorganic salts, the known vitamins, and mixtures of highly purified amino acids. Their diet also included a large brown "candy," which contained a concentrated liver extract to supply unknown vitamins, sugar, and peppermint oil to provide a "never-to-be-forgotten taste."
The study used a chemical measurement called nitrogen balance to determine whether the subjects were getting enough usable protein from the mixture. From his experiments, Dr. Rose found that only eight of the ten amino acids essential to rats were also essential to men -- we were better at making two amino acids than rats. When an essential amino acid was given in insufficient amounts for approximately two days, all subjects complained bitterly 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.
Through his studies, Dr. Rose also determined a minimum level of intake for each of the eight essential amino acids.10 He found small amounts of variation in individual needs among his subjects. 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 subject, and then doubled that amount for a "recommended requirement" -- described as a definitely safe intake. It is important to realize that his higher requirement is easily met by a diet centered around any single starchy vegetable. Even in children, as long as energy needs are satisfied by starch, protein needs are automatically satisfied in almost every situation because of the basic and complete design of the food. These investigations were completed by the spring of 1952, resulting in sixteen papers in The Journal of Biological Chemistry that are considered classic contributions in the history of nutrition for the benefit of human beings.
The results of Dr. Rose`s studies are summarized in the following chart, under "minimum requirements". From the chart, it is clear that vegetable foods contain more than enough of all the amino acids essential for humans.11
(see chart)
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