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High protein diets are diets in which 20% or more of the total daily calories comes from proteins. A very high protein diet is one where 30% or more of the total daily calories comes from protein. By comparison, in the average American diet about 12–16% of calories come from protein.
High protein diets have been popular off and on since the 1960s. In the 1960s, Dr. Maxwell Stillman of the Stillman Diet was one of the first to advocate a high protein, no carbohydrate, low fat diet for fast weight loss. In the 1990s, diet books promoting high protein diets began to appear on bestseller lists. The most popular of these “new” high protein diets was the Atkins Diet. Other high protein diets include the Zone Diet, Protein Power, and Sugar Busters. These diets are the heirs to the Stillman Diet, slightly modified to include some carbohydrates, and repackaged with some updated terminology and scientific explanations. They encourage high protein diets for weight loss and/or for bodybuilding.
All human protein is made from about 20 different small molecules called amino acids. Out of these 20 amino acids, nine are considered essential amino acids. They are essential because the body cannot make them from other nutrients and they must be obtained fully formed from diet.
Both animals and plants are sources of protein. Animal protein has the higher biological value because it is a complete protein. Complete proteins contain all nine essential amino acids. Animal proteins include meat, poultry, fish, egg whites, and dairy products.
Plant proteins have a lower biological value because they are incomplete proteins that do not contain all nine essential amino acids. Some plants are better sources of protein than others because they lack only one or two essential amino acid. Better plant proteins include dried beans and bean products such as tofu (made from soybeans), nuts, and grains such as corn and quinoa. Many cultures have developed dishes such as red beans and rice or corn tortillas and beans that combine these incomplete proteins in the same meal to provide all the essential amino acids needed for health.
Extra amino acids are not stored in the body. Instead, they are split apart by enzymes, and the part containing nitrogen is excreted by the kidney in urine, while the remainder is either converted into glucose (a simple sugar) and used for energy or stored as glyco-gen, a compound that can later be reconverted into glucose.
High protein diets are also high in saturated fats. Saturated fats are animal fats. They are considered “bad” fats because they raise the level of LDL cholesterol (“bad” cholesterol) in the blood. High LDL cholesterol levels are associated with an increased the risk of heart disease. High protein diets also restrict calories by severely restricting carbohydrates. Whole-grain carbohydrates are a significant source of B-com-plex vitamins. There are groups who need extra protein—rapidly growing adolescents, pregnant and nursing women, bodybuilders, endurance athletes, and some cancer patients— but these groups need to increase protein as part of a well-balanced diet.
High protein diets do promote fast initial weight loss, although most of the loss comes from losing water. The reason for this is that they drive the body into a state called ketosis. The body prefers to break down carbohydrates into glucose and use that glucose for energy. When the body is starved for carbohydrates, it begins converting fat into glucose. The process of converting fat into glucose releases water molecules which then leave the body as urine.
Dieters, of course, want to burn fat, but when they burn fat exclusively, a side effect of this reaction is that molecules called ketones build up in the blood. If the body is deprived of carbohydrates for a long time, these ketones accumulate and cause metabolic imbalances that can seriously harm the kidney and other organs. Ketones are part of the body’s defense against starvation. They suppress appetite. They also cause bad breath.
High-protein diets offer fast weight loss. The Stillman Diet claims an individual can lose up to 30 lb (13.5 kg) in 28 days. Some high protein diets also claim
health benefits. The Zone diet claims it will improve physical and mental performance, prevent chronic cardiovascular diseases, improve immune system functioning, decrease signs of aging, and increase longevity.
Rapid weight loss does occur with high protein diets, but much of the loss comes from losing water. This weight soon returns when the dieter goes off the diet. Other health claims have not been proven by any rigorous, scholarly research studies.
The risk of kidney damage is greater in individuals with poor kidney function who choose a high protein diet. High protein diets put an extra workload on the kidney because the nitrogen-containing part of excess amino acids is split off and has to be removed from the body in urine. Although this is not usually a problem for healthy kidneys, it can cause more damage in kidneys whose functioning is already reduced.
High protein diets have come in for a lot of criticism, even though several studies have shown that the Atkins diet is not as problematic as was originally thought. Nutritionists find high protein diets, especially high protein, high fat, severely carbohydrate restricted diets, to be unhealthy, unbalanced, and generally unnecessary because of the well-documented risks outlined above. The public, however, has embraced high-protein diets such as the Zone Diet and the Atkins Diet, at least until the next new diet comes along. Bodybuilders, weightlifters, and others wishing to gain muscle mass also look favorably on high protein diets. The Mayo Clinic concludes that high protein diets are probably not harmful to healthy individuals with good kidney function. The American Heart Association condemns these diets because they appear to increase the risk of cardiovascular disease. No studies have been done on the long-term effects of high-protein diets.
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Tish Davidson, A.M.