Carnitine

Carnitine, a derivative of the amino acid lysine, is naturally produced in the body and plays an important role in energy metabolism. High amounts of carnitine can be found in food sources including meat, dairy, poultry, and fish products. Carnitine supplementation is thought to enhance athletic performance through improving muscle fatty acid oxidation, replacing diminished muscle carnitine during training, and improving muscle resistance to fatigue. (Brass 2000)

Carnitine transports fatty acid chains into the mitochondria where they are oxidized to produce energy. Carnitine is found in high concentrations in cells that use fatty acids for fuel, namely cardiac and skeletal muscle. The theoretical basis for improving exercise performance comes from the increase in muscle carnitine content resulting from the greater intake of carnitine. However, there is insufficient evidence that supplemental carnitine improves exercise performance outcomes and dietary supplementation of carnitine is not necessary in healthy individuals, as sufficient amounts to meet daily needs are produced by the liver and kidneys. (Dietary Supplements 2017) 

Studies evaluating performance outcomes such as maximal oxygen uptake, perceived exertion, and athletic performance demonstrate no effect with carnitine supplementation. Similarly, studies looking at metabolic outcomes such as oxygen consumption, blood lactate, and respiratory quotient also found no effect from supplementing carnitine. (Brass 2000)

Despite the lack of consistent research for improving performance, there is emerging evidence that carnitine supplementation may improve recovery following exercise due to carnitine's antioxidant effects. Fielding and colleagues (2018) concluded "scientific data indicates that the athletic population can benefit from L-carnitine intake as it attenuates the side effects of high-intensity training by reducing the magnitude of exercise-induced hypoxia and muscle injury". 

In theory, carnitine supplementation may work for increasing exercise performance in healthy individuals, but the available research evidence does not consistently support this assumption. No definitive dosing or recommendations can be made for supplementation of carnitine to improve athletic performance based on the existing inconclusive data. Carnitine supplementation shows more promise in facilitating the recovery process following exercise and a shift towards focusing on the mechanisms responsible for this may have better outcomes, but further research is necessary. (Brass 2000, Fielding 2018)

References

Brass EP (2000). Supplemental carnitine and exercise, The American Journal of Clinical Nutrition. 72(2):618S–623S.

Fielding RA, Riede L, Lugo JP, Bellamine A (2018). l-Carnitine Supplementation in Recovery after Exercise. Nutrients.

National Institutes of Health. Carnitine (2017). Office of Dietary Supplements. Retrieved March 21, 2019, from https://ods.od.nih.gov/factsheets/Carnitine-HealthProfessional/

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