Of the 20 amino acids that aid biological function, 10 are not produced by the body and must be ingested through food. These amino acids are, in no particular order:
Each of these amino acids is important in the body's biological function and continuing health. For example, lysine aids the absorption of calcium and the formation of collagen, which are important for bone and joint health, and also helps to regulate fat and cholesterol processing. Lack of lysine can lead to brittle bones, weak joints, and increased fat storage.
Some other effects of amino acid deficiency include exhaustion, decreased mental clarity, heart disease, increased risk of cancer and stroke, muscle and bone loss, decreased immune function, depression, and digestive problems. These symptoms can manifest quickly or slowly depending on the diet and other issues; many supplement companies sell single or multiple amino acid pills, although these are not regulated for safety and efficacy by the FDA.
In general, people consume enough amino acids through their normal diets. Meat diets contain proper and even excess levels of amino acids, since meat protein are "complete" and contain all the necessary amino acids. The body does not store excess amino acids, and so they must be re-ingested every day. Vegetarian diets can be lax in amino acids, but consumption of soy products and eggs can replace meats.