Carnitine is an amino acid-like substance that is synthesized in the body from the amino acid lysine. Carnitine is important in the metabolism of fat and energy production within the body, and helps maintain healthy heart, skeletal muscle and liver function. Carnitine may also improve athletic ability. Some carnitine may be obtained from dietary sources, primarily meat since vegetables and fruit contain relatively little carnitine. Athletes are most at risk from carnitine deficiency; vegetarians may also be at risk of carnitine deficiency if their diet contains low levels of lysine. Carnitine supplements are available in several chemical forms- only the L-form of carnitine is biologically active (the D-form is inactive). Carnitine levels are reduced by a high fat diet, certain drugs (e.g. valproic acid antibiotics) or metabolic stress.