"An explicit definition of a high-protein diet has not yet been developed by the Food and Nutrition Board of the Institute of Medicine, but typically diets high in protein are considered those that derive more than 30 percent of calories from protein. Many people follow high-protein diets because marketers tout protein’s ability to stimulate weight loss. Following high-protein diets increases weight loss in some people, but the number of individuals who remain on this type of diet is low, and many people who stop regain the weight they had lost. There may be health consequences of remaining on high-protein diets for the long term, but clinical trials are ongoing or scheduled to examine this hypothesis further. Observational studies suggest diets high in animal protein, specifically those in which the primary protein source is red meat, are linked to a higher risk for kidney stones, kidney disease, liver malfunction, colorectal cancer, and osteoporosis. However, diets that include lots of red meat are also high in saturated fat and cholesterol and are sometimes linked to unhealthy lifestyles, so it is difficult to conclude that the high protein content is the culprit. High-protein diets appear to increase the progression of kidney disease and liver malfunction in people who already have kidney or liver malfunction, and not to cause these problems. A high intake of red meat and processed meat is associated with a significant increase in colon cancer risk, although the exact mechanism is not known and requires further study. Some scientists hypothesize that high-protein diets may accelerate bone-tissue loss because under some conditions the acids in protein block absorption of calcium in the gut and, once in the blood, amino acids promote calcium loss from bone; however, these effects have not been consistently observed. The scientific data on high-protein diets and increased risk for osteoporosis remains highly controversial. High-protein diets can restrict other essential nutrients. The American Heart Association states that high-protein diets are not recommended because they restrict healthful foods that provide essential nutrients and do not provide the variety of foods needed to adequately meet nutritional needs. Individuals who follow these diets are therefore at risk for compromised vitamin and mineral intake, as well as potential cardiac, renal, bone, and liver abnormalities overall. As with any nutrient, protein must be eaten in proper amounts. Moderation and variety are key strategies to achieving a healthy diet."