Protein Excess
Many of the world's people struggle to obtain enough food and enough protein to keep themselves alive, but in the developed countries protein is so abundant that problems of protein excess are seen. There are no benefits, and there are risks associated with the overconsumption of protein. For one thing, as we have said before, protein-rich foods are often high-fat foods that contribute to obesity, with its accompanying health risks. In addition to the effects of fat, high levels of animal protein itself may raise cholesterol levels, thus contributing to heart disease. In addition, infants and children do not adjust well to diets containing large amounts of protein; their body composition is altered. Animals fed high-protein diets experience a "protein overload effect," seen in the enlargement of their livers and kidneys. In human beings, high-protein diets eaten over a lifetime may cause problems in kidney function.
Animals experimentally fed high-protein diets of the same nature as those that Americans typically eat also experience losses of the essential mineral zinc from their tissues as they age. Such zinc excretion is also seen in pregnant women and in infants on protein supplements. The use of such supplements during pregnancy may do more harm than good, even to undernourished women. In infants their use has been linked to deficits in cognitive development.
Protein also creates a demand for certain vitamins for its metabolism; vitamin B6 is an example. An overabundance of protein without accompanying vitamin B6 can cause a deficiency of the vitamin, and such deficiencies are suspected of contributing to our population's high incidence of atherosclerosis.10 High dietary protein also increases the tendency to obesity, a finding in direct contrast to the popular belief that such diets cause people to "burn off fat." Fed low-protein diets, even with ample calories from carbohydrate, obese subjects can lose weight.
Diets high in protein may also increase the body's excretion of calcium, depleting the bones of their chief mineral. Some argue that food sources of excess protein do not promote calcium excretion but that protein or amino acid supplements do so. In keeping with the first possibility, the Committee on RDA has suggested an upper limit for protein intake of no more than twice the RDA amount. In a world in which protein deficiency is such a threat to so many, it is ironic that some people in developed countries should be overconsuming protein.
While eating excess protein is clearly ill advised, taking protein or amino acid supplements (except for abnormal conditions, on competent medical advice) is even more so. The accompanying Consumer Caution, "Protein and Amino Acid Supplements," tells why.
Protein and Amino Acid Supplements
Why do people take protein supplements? Athletes take them to build muscle. Dieters take them to spare their bodies' protein while losing weight. Women take them to improve the strength of their fingernails. People take individual amino acids, too—to cure herpes, to make themselves sleep better, to relieve pain and depression. Do protein and amino acid supplements really do any of these things? Almost never. Are they safe? No.
Muscle work builds muscle; protein supplements do not, and athletes do not need them. Food energy spares body protein; fat and carbohydrate serve this purpose equally well, and carbohydrate is safer (see Chapter 10 for details). Fingernails remain unaffected by protein supplements, provided the diet is otherwise adequate in protein. This chapter demonstrates that no decent diet fails to supply enough protein, so protein supplements never are needed by the normal, healthy person.
Furthermore, protein supplements are expensive and less well digested than protein-rich food; and when used as a replacement for such food, they are often downright dangerous. The "liquid protein" diet, advocated some years ago for weight loss, caused death in many users, and even the 'physician-supervised protein-sparing modified fast (also based on liquid protein) can cause abnormal heart rhythms.
As for amino acid supplements, they, too, are unnecessary, and the body is not adapted to handle them. The body is designed to handle whole proteins best. It breaks them into manageable pieces (dipeptides and tripeptides), then splits these a few at a time, simultaneously absorbing them into the blood. When proteins are predigested in a laboratory and served up as mixtures of single amino acids, they are less well digested and absorbed because they overwhelm the absorptive mechanism and not all can be accommodated. When amino acids are presented singly, severe imbalances and toxicities can occur. Groups of chemically similar amino acids compete for the carriers that absorb them into the blood, and an excess of one can create such demand for a carrier that it prevents the absorption of another. The result is a deficiency. Many amino acids are toxic when taken in excess. In some cases "excess" means not very much above normal daily intake levels.
In two cases recommendations for amino acids have led to widespread public use—lysine to prevent or to relieve the infections that cause herpes sores on the mouth or genital organs and tryptophan to relieve pain, depression, and insomnia. In both cases enthusiastic, popular reports and careful scientific experiments are at odds. Lysine does not relieve or cure herpes infections, and if long-term use helps prevent them, it does so only in some individuals and with unknown associated risks. Tryptophan does have some interesting effects with respect to pain and sleep in responsive individuals, as Controversy 6 explains further, but people taking large doses may be damaging their livers. In fact, a blood disorder characterized by severe muscle and joint pain, limb swelling, extremely high fever, and, in at least one case, death has been linked to tryptophan supplements.* The Food and Drug Administration (FDA) has requested a recall of tryptophan supplements, and if you own a bottle of tryptophan pills, throw it out. It is safer to take amino acids in protein foods with a little carbohydrate to facilitate their use—a turkey sandwich, for example.
Many of the chapters of this book present evidence on purified nutrients added to foods or taken singly. The Consumer Caution of Chapter 4 showed that the enrichment of a nutritionally inferior food (refined bread) with four added nutrients left it still deficient in many others. The Chapter 5 Consumer Caution showed that an excess of lecithin provides no benefits and causes side effects. With amino acids, the same thing is true. Even with all that we know about science, it is hard to improve on nature.
Sources: R. A. Lantigua and coauthors, Cardiac arrhythmias associated with a liquid protein diet for the treatment of obesity, New England Journal of Medicine 303 (1980): 735-738; N. J. Benevenga and R. D. Steele, Adverse effects of excessive consumption of amino acids, Annual Review of Nutrition 4 (1984): 157-181; Myth of the month: Lysine for herpes, Nutrition and the MD, December 1984, p. 4; L. J. Fitten, J. Profita, and T. G. Bidder, L-tryptophan as a hypnotic in special patients, Journal of the American Geriatrics Society 33 (1985): 294-297; M. E. Trulson and H. W. Sampson, Ultrastructural changes of the liver following L-tryptophan ingestion, Journal of Nutrition 116 (1986): 1109-1115; Eosinophilia-myalgia syndrome and L-tryptophan-containing products—New Mexico, Minnesota, Oregon, and New York, 1989, MMWR—Morbidity and Mortality Weekly Report 38 (1989): 785-788.
NUTRITION CONCEPTS AND CONTROVERSIES
Eva May Nunnelley Hamilton / Eleanor Noss Whitney / Frances Sienkiewicz Sizer
Fifth Edition Prepared by Eleanor Noss Whitney / Zrances Sienkiewicz Sizer
WEST PUBLISHING COMPANY