L-carnitine can boost your endurance… But give it time


19.03.20 at 9:54 am

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Maybe you’ve heard of/used L-carnitine, the amino acid derivative a lot of research shows can boost sports performance?

L-carnitine mightn’t have the sports nutrition ubiquity of whey powder or caffeine in the endurance sports world, but it is probably in the top-10 of performance-enhancing food supplements in terms of science backing.

If you do use it, perhaps you’ve raised an eyebrow after British middle-distance runner, double Gold Olympian (twice) and Knight of the Realm, Mo Farah, was found back-tracking over potentially misusing it – aka having a coach inject him with it although he claims the dose was below the World Anti-Doping Agency (WADA) threshold of 50ml in six hours.

Mo Farah L-Carnitine

Given his weird L-Carnitine denial and all the smoke that surrounds Sir Mo’s career amid his lengthy association with now banned coach Alberto Salazar from the Nike Oregon Project; plus other drug-linked coaches like Jama Aden; as well as lame excuses for missing out-of-competition doping controls (didn’t hear doorbell)… one could be forgiven for thinking a supplement like L-carnitine might be one of those grey zone substances like say, cortisone, most self-respecting, clean endurance sports nuts are best steering well clear of.

Why would a pro like Sir Mo deny using a legal supplement? He says he forgot about the injection…rightio then…


So what’s the deal with L-carnitine? Is it safe, legal and can it help me on long swims, bike rides or runs? In a nutshell, yes, yes and yes. It is safe, it is legal at most available oral doses and some fairly solid science says it can boost performance if taken the right way over the right period of time.

L-carnitine supplements boost the body’s own liver and kidney-based production of a nutrient that can benefit muscle performance, burn fat and reduce fatigue.

On a cellular level, these benefits are achieved because L-carnitine helps fatty acids get into cellular mitochondria where it is converted to energy, while moving metabolic waste away. Powerful stuff, really.

Some research shows it can boost performance by as much as a whopping 11% over a period of 4-6 months. The lead researcher of that and many other L-carnitine based studies, the eminent professor Paul Greenhaff told The Draft of his research between evacuating his University of Nottingham Medical School office amid the COVID-19 lockdown.

“There are two primary routes for L-carnitine: one via modulating carbohydrate flux regulation; the other by modulating fat oxidation,” the professor of Muscle Metabolism, Faculty of Medicine & Health Sciences said.

Back in 2011 when he and his co-researchers wrote of the above study they said it is, “the first demonstration that human muscle total carnitine can be increased by dietary means and results in muscle glycogen sparing during low-intensity exercise.”


Professor Greenhaff emphasises the importance of consuming L-carnitine with insulin-boosting carbohydrates to achieve efficacious L-carnitine levels in the muscle where it matters most.

Dr Mark Tallon, PhD, UK-based founder of triathlon training service TriathlonLab and food law consultancy Legal Foods, says carb levels of around 90g taken with 1g of L-carnitine three times a day has been shown to significantly increase muscular/cellular L-carnitine levels compared to L-carnitine taken in isolation. But it takes time.

Perhaps one of the reasons L-carnitine does not possess a higher profile is that its benefits are far from immediate. Professor Greenhaff recommends 4-6 months of diligent carb-mixed L-carnitine consumption for the fat oxidisation, fatigue reduction and muscle-boosting benefits to really kick in.

Due to this longevity, for Dr Tallon, “There is no solid data on nutrient timing.”

 “The main issue is to increase the free pool of L-carnitine. Theoretically, I would say not to take carnitine prior to or within an hour post-exercise as it may get oxidised as a fuel rather than stored.”


Despite a PubMed search for ‘L-carnitine supplementation’ returning more than 1700 results, the EU’s food science agency, the European Food Safety Authority, in 2011 rejected a swathe of potential L-Carnitine’s effects. It claimed the data did not link L-carnitine to specific performance endpoints strongly enough. Why?

“Because ingestion of L-carnitine in the absence of carbohydrate and over at least a four month period will not increase muscle total L-carnitine content,” said professor Greenhaff of the notoriously conservative institution that has also rejected the performance benefits of the likes of whey protein, probiotics and even, heavens to Murgatroyd, water.

Both professor Greenhaff and Dr Tallon agreed EFSA could be persuaded if the right kind of data dossier was submitted to its health claims assessment panel.

Some research indicates L-Carnitine supplementation can benefit vegans and vegetarians who typically have lower L-Carnitine levels than flesh eaters, and retain it better, perhaps indicating “the body recognises the deficiency.”


In regard to Sir Mo Farah’s case, Dr Tallon said IV delivery was not necessarily an issue, but questioned whether even a needle leading up to a race could deliver an efficacious dose, “especially in the absence of insulin.” Insulin is banned by WADA with its use only permitted via Therapeutic Use Exemption (TUE) for diabetics.

“So the question is are athletes infused with L-Carnitine also being infused insulin?”


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