Lysine & Leucine

Lysine and leucine are two of nine essential amino acids -- the building blocks of protein. An amino acid is categorized essential when the body can't make it on its own; instead, you have to obtain it through your diet. Both these amino acids play vital roles in protein synthesis and can help promote the recovery and growth of muscle tissue. This effect has made lysine and leucine a common ingredient in many dietary supplements and muscle growth products such as protein shakes.


Lysine is an essential amino acid that is important for proper body growth. It plays a vital role in converting fatty acids into energy, which it does by producing carnitine, a nutrient that can help lower cholesterol. Lysine appears to help the body absorb calcium. The University of Maryland Medical Center (UMMC) also notes that studies suggest that lysine may offer protection against herpes and relieve osteoporosis symptoms due to its affects on calcium. Besides dietary supplements, you can obtain lysine from red meat, pork and poultry, as well as cheese, some fish, nuts, eggs, tofu, beans and brewer's yeast.


Leucine is one of three branched-chain amino acids, or BCAA. The other two BCAAs are isoleucine and valine. In addition to promoting protein synthesis, like lysine, leucine also contributes to several metabolic processes. Research done by Donald Layman of the University of Illinois, however, suggests that leucine's primary role is to aid in the synthesis of protein structures first before dedicating itself to its other metabolic functions. Leucine, along with the other BCAAs, account for approximately 15 to 25 percent of total protein intake in the average diet. Dairy products are considered to be especially rich in BCAAs.

Leucine and Lysine Intake

Research suggests that when leucine and lysine are taken for protein supplementation, the two essential amino acids rely on each other to achieve their metabolic roles. A study published in the June 1981 issue of the "American Journal of Physiology" found that when lysine metabolizes, it encourages leucine and other essential amino acids to perform their protein synthesis functions more efficiently. The levels of leucine and lysine also seemingly have an effect on the maintenance of nitrogen and other amino acids in your body. In the study, one group of participants fasted, while the other group received food. The response of leucine and lysine was affected by the presence of food.


The health and fitness industry has latched on to the potential benefits of lysine and leucine. The appeal of fast muscle recovery and muscle tissue growth has led to the marketing of many products as essential amino acid-containing supplements. The hype, however, often overshadows the evidence. While lysine and leucine have proven effective in helping your muscles recover and grow, they are not a magic bullet for large muscles. Actual results depend more on the intensity of your strength training routine and diet. Furthermore, the University of Maryland Medical Center warns that taking too much lysine can cause gallstones. You should consult with your doctor before taking lysine or any other supplements.