Significance

• Leucine is used by the liver, fat cells and muscle cells. It helps regulate blood sugar levels and growth hormone production, as well as heal damage to the skin, skeletal system and muscles.
  
  

Dietary Sources

• Leucine is found in animal proteins, brown rice, legumes, whole wheat and tree nuts. It also is sometimes added to processed foods as a flavor enhancer. Whey protein is the best source. We need at least 16 mg. of leucine per kilogram (2.2 pounds) of body weight daily. People who don't get enough dietary leucine--such as vegetarians--may experience headaches, dizziness, fatigue and irritability. Most meat-eaters get ample leucine to maintain health.
  
  

Muscle Mechanism

• Bodybuilders use leucine mostly to enhance muscle "recovery." Exercise both breaks down and stimulates the rebuilding of muscle cells; bodybuilders use nutrients to keep their bodies from become catabolic, a state in which the body starts breaking down muscle for fuel. An adequate supply of leucine helps the rebuilding process outrun the breakdown process.
  
  According to studies cited by the American Journal of Physiology in 2002, leucine is about 10 times as useful as other amino acids in encouraging a positive protein balance after exercise. Research also has shown that leucine is better at aiding muscle recovery than protein and carbohydrate supplements without leucine. By helping raise insulin levels in the blood, leucine gives muscles the ability to draw in more nutrients. Studies on rats show leucine has the ability to increase protein synthesis and inhibit protein breakdown.
  
  

Considerations

• Leucine in high doses can increase cholesterol levels. Nutritionists recommend getting leucine from low-cholesterol sources such as fish and beans rather than from red meat and eggs. Taken alone, leucine can decrease the levels of isoleucine and valine, two other branched chain amino acids (BCAAs); it should always be taken with other amino acids.
  
  

Potential

• A Brazilian study showed low-dose leucine helped dieters lose more fat and less muscle. Researchers are also studying the use of leucine in treating Parkinson's disease, a degenerative neuro-muscular ailment, and phenylketonuria, an inborn error of the digestive system.