After a paper published by the American Dietetic Association in 1987, high protein intakes or excessive amino acids supplements have not been demonstrated to increase athletic performance. After nutritionist, the plain old answer of "eat balanced, eat normal" still remains the best known method: 0.8 grams of protein for an adult for each kilogram of body weight (recommended dietary allowance). On the other hand, more studies on athletes doing intensive training have suggested that as protein is broken down in the muscles and converted into energy, a higher intake of 1g might be necessary (so that an 82kg person might need 82 grams of protein instead of 66). Considering that a hamburger with one slice of cheese is already 40 grams of protein, reaching the RDA is not that hard, so that most Americans consume in the end twice as much protein as needed, whether they are physically active or not.
Older researches said that taking too much protein won't do any harm, but more recent studies sustain the contrary. Too much protein and amino acids supplements can be harmful. Extra amino acids can cause long-term kidney damage and interfere with the normal digestion of protein. This is explained by how kidney work: "one of the kidneys' essential roles is handling the nitrogen-containing waste products produced as the body metabolizes the amino acids consumed from proteins in the diet" (Stockton). More amino acids and proteins than needed put an extra stress on the kidneys , steadily decreasing the organ's capacity, leading to failures. Extra, amino acids alone modify the digestive process. Supplements cause the amino acids to be excreted from the body without being taken into blood anymore, as they are crowded out.
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