Leucine works with the amino acids isoleucine and valine to repair muscles, regulate blood sugar, and provide the body with energy. It also increases production of growth hormones, and helps burn visceral fat, which is located in the deepest layers of the body and the least responsive to dieting and exercise.
Leucine, isoleucine, and valine are branched-chain amino acids (BCAAs), and all three of them help promote muscle recovery after exercise. Leucine is the most effective BCAA for preventing muscle loss because it breaks down and is converted to glucose more quickly than isoleucine and valine. Increased glucose supplies prevent the body’s cannibalization of muscle for energy during intense workouts, so it is no surprise that this amino acid supplement is popular among professional body builders. Leucine also promotes the healing of bones, skin, and muscle tissue after traumatic injury, and is often recommended for those recovering from surgery.
Because it is so easily converted to glucose, leucine helps to regulate blood sugar; a deficiency of leucine produces symptoms similar to those of hypoglycemia, which may include headaches, dizziness, fatigue, depression, confusion, and irritability.
Natural sources of leucine include brown rice, beans, meat, nuts, soy flour, and whole wheat. Leucine is an essential amino acid, which means that it cannot be manufactured in the body and must be obtained through dietary sources. People that exercise a lot, have a low-protein diet, or are seriously trying to build muscle mass should consider leucine supplementation. Leucine is also available in stand-alone supplemental form, but should always be taken together with the other two branched-chain amino acids, isoleucine and valine. The ideal balance is 2 milligrams of leucine and valine for each 1 milligram of isoleucine. Combination supplements that provide all three of the BCAAs may be more convenient.
An excessively high intake of leucine has also been linked to the development of pellagra, a deficiency of the vitamin niacin that causes dermatitis, diarrhea, and mental disorders. Too much leucine in the diet can disrupt liver and kidney function and increase the amount of ammonia in the body. People with impaired liver or kidney function should not take isoleucine without first consulting a physician, as large doses of amino acids may aggravate these conditions.