Proteins, composed of amino acids, are indispensable in the diet. They build, maintain, and repair the body. Without dietary protein, growth and all bodily functions would cease.
The human body manufactures "nonessential" amino acids, and requires ingestion of about eight or nine "essential" amino acids. These can come from either animal or vegetable sources, such as eggs, milk, fish, meat, poultry, soybeans, and |nuts|. High quality proteins, such as eggs, meat or fish, supply all essential amino acids needed in the diet and are called "complete proteins". The "incomplete proteins" supply only a few of the essential amino acids and need to be eaten in combination with other protein sources for balance. The peanut butter sandwich is an example: the bread is rich in methionine, and the peanut butter is rich in lysine.
As with most foods, too much protein in our diet can cause problems. Excess protein breaks down in the body for energy (after |carbohydrates| and fat are used), or, if not used, it's converted to fat. A diet high in animal protein increases the loss of calcium in the body. Also, excessive amounts of protein can produce |dehydration|, ~diarrhea~, and may aggravate |liver| or |kidney| disease as well. Only strength-building |exercise|, not more protein or supplements, will build muscles.
