If you’ve been following recent sports news, you have probably seen headlines accusing Mo Farah of taking inappropriate amounts of carnitine. Another recent article listed all the supplements taken by Shannon Rowbury before the 2016 Rio Olympics. One of the many supplements listed was Hammer Mito caps, which contain 250 mg of carnitine per tablet. If you’re like me, you might automatically assume that carnitine is beneficial for performance just because these highly successful runners are taking it. I certainly was curious and decided to research this substance that I knew very little about.

Carnitine is a compound made by the body, mainly in the liver. Carnitine can also be found in food. Animal products tend to contain more carnitine than plant products. In general, the redder the meat, the higher the carnitine content. While muscle can’t make carnitine, it does contain the body’s largest stores of carnitine. Carnitine plays a role in mitochondrial fat oxidation, and carnitine’s role in this process is why many claim that it can be used to improve sports performance. The claim is that by taking a carnitine supplement, it will increase the use of fat as energy during exercise instead of carbohydrates stored as glycogen in the muscle. In endurance events such as the marathon, “hitting the wall” is associated with muscle glycogen depletion. The idea is that this could be avoided by using fat stores instead. Carnitine is not banned from use in sports within a limited dose. However, injecting more than 50 mL of carnitine within 6 hours intervals is NOT allowed. This is what Mo Farah is being accused of.

If you were to type “carnitine” into a google search engine, most sites would claim a performance benefit with carnitine supplementation. However, most of these sites are also trying to sell carnitine supplement (AKA huge conflict of interest). When I began to read studies on google scholar without this conflict of interest, most showed no benefits in sports performance with carnitine supplementation. The lack of benefits is probably because taking a carnitine supplement fails to increase muscle carnitine stores. After taking a carnitine supplement, most of it is not absorbed but rather, peed out. Very large doses of carnitine supplements over an extended time period would be needed to change carnitine muscle stores. This fact is probably why carnitine is banned in sports with large injections.

Another reason that carnitine supplementation may not improve endurance sports’ performance is because carnitine might not be the compound that limits fat use during exercise. In other words, even if we were able to significantly increase our muscle carnitine stores from carnitine supplements, it may not increase fat use during endurance sports. Additionally, the labels of carnitine supplements may be misleading. In a study of 12 over-the-counter carnitine supplements, the carnitine content was only 52% of what was on the label.

In conclusion, there is no strong evidence showing improved fat metabolism with carnitine supplementation. My recommendation: save your money and don’t take a carnitine supplement (unless you want really expensive pee) until a clear benefit can be proven.

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