Carnitine (Typically L-Carnitine)

L-carnitine is a common name for beta-hydroxy butyrate, a quaternary amine that was first discovered in muscles in the early 1900s. It is mainly involved in transporting long-chain fatty acids that reside inside cells into the mitochondria of the cells, where they are metabolized. Carnitine increases blood flow by improving fatty acid oxidation in the artery walls, and it detoxifies ammonia, a by-product of protein breakdown that is associated with early fatigue.⁴⁴We synthesize carnitine from the amino acids lysine and methionine, and it is found in abundant quantities in all meats and dairy products, so a deficiency is unlikely. If a deficiency occurs, it is most likely in vegetarians who avoid consumption of dairy products. With an adequate intake of meats or dairy products, there is little reason to take this relatively expensive supplement. Although never tested, it is possible that pure vegans might benefit from L-carnitine supplementation if they perform high-intensity exercise.

Carnitine is thought to spare muscle glycogen breakdown and decrease lactic acid production, but studies of carnitine generally show no benefit for low-intensity endurance activities.⁴⁵ Some studies, however, have demonstrated a benefit in high-intensity activities when consumed either just before the activity or for several days. The typical dose is between 1 and 2 grams per day, but the safety of L-carnitine supplementation has not been adequately tested. The type of carnitine taken is also important. There are reports that DL-carnitine supplementation (a less expensive form of carnitine) may cause muscle weakness.⁴⁶ Therefore, if an athlete insists on taking this supplement, only the L-carnitine form should be considered.