Most of you probably already know that L-carnitine supplementation does not lead to increased body fat burning - this theory was already disproved in the 1990s.
However, L-carnitine may have other benefits in our body. It appears that its chronic supplementation over several months in combination with carbohydrates (to facilitate transport) can positively affect body composition, increase tolerance to physical training and even boost cognitive function in the elderly. In addition, L-carnitine, due to its antioxidant activities, also appears to help reduce muscle damage after training and thus speed recovery. Some studies have also pointed to carnitine's ability to increase sperm motility.
On the other hand, it turns out that long-term supplementation with L-carnitine may have its risks. L-carnitine increases plasma levels of TMAO (trimethylamine oxide), which is often associated with proatherogenic effects and increased risk of cardiovascular disease. For example, a 2019 study found that three months of oral carnitine supplementation increased TMAO levels in healthy women up to 10-fold (Samulak et al, 2019). However, more studies are needed to further confirm the potentially negative impact of TMAO and specifically L-carnitine on our circulatory health.
Literature
SAWICKA, Angelika K.; RENZI, Gianluca; OLEK, Robert A. The bright and the dark sides of L-carnitine supplementation: a systematic review. Journal of the International Society of Sports Nutrition, 2020, 17.1: 1-10.
Heinonen, Olli J. „Carnitine and physical exercise.“ Sports Medicine 22.2 (1996): 109-132. Villani
Rudolph G., et al. „L-Carnitine supplementation combined with aerobic training does not promote weight loss in moderately obese women.“ International journal of sport nutrition and exercise metabolism 10.2 (2000): 199-207.
LENZI, Andrea, et al. A placebo-controlled double-blind randomized trial of the use of combined l-carnitine and l-acetyl-carnitine treatment in men with asthenozoospermia. Fertility and sterility, 2004, 81.6: 1578-1584.
FIELDING, Roger, et al. L-carnitine supplementation in recovery after exercise. Nutrients, 2018, 10.3: 349.
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