L-carnitine
For weight loss the effect is small at best; healthy people don't need it
What it is
A compound that helps carry long-chain fatty acids into the mitochondria, where they are oxidised to produce energy. The body makes it itself in the liver, kidneys and brain; in food it comes mostly from animal products.
Benefits
Most data suggest supplements do not markedly affect fat metabolism, exercise performance or weight loss (ISSN). In a meta-analysis of 9 trials, people taking carnitine lost on average 1.33 kg more than those on placebo; NIH calls the results equivocal and says larger studies are needed. Evidence on athletic performance is mixed (NIH).
Dose
There are no intake values: healthy children and adults do not need carnitine from food or supplements, because the liver and kidneys make enough (NIH). The AIS protocol for athletes: 1.4–3 g of L-carnitine (2–4 g of L-carnitine L-tartrate) a day, split into 2 doses, for 12 weeks or longer.
When to take it
2 doses, morning and night, each with a meal containing 80 g of carbohydrate: without carbohydrate, muscle carnitine did not change in most studies (AIS). AIS itself notes that this much carbohydrate 2 times a day is unlikely to fit your calorie needs.
Who it's for
In theory, people competing in endurance events longer than 30 minutes or playing team sports, but studies have shown no consistent effect (AIS). Vegetarians may respond more strongly. Primary and secondary carnitine deficiency are resolved with high doses of supplemental carnitine (NIH).
Who can skip it
Healthy people, vegans included: carnitine deficiency is rare even in them (AIS), and the body's own synthesis is sufficient (NIH). Also anyone expecting weight loss: evidence that carnitine enhances fat loss is lacking (AIS).
Forms
The main forms in supplements are L-carnitine and acetyl-L-carnitine (NIH ODS). Supplemental L-carnitine is absorbed at 14–18%, much less than from food (63–75%). The bioavailability of acetyl-L-carnitine has not been well studied. The source read contains no comparative data on L-carnitine L-tartrate.
Safety
No upper level has been set. About 3 g a day can cause nausea, vomiting, abdominal cramps, diarrhoea and a fishy body odour. It can cause seizures in people with seizure disorders and muscle weakness in people with uremia. Gut bacteria turn unabsorbed carnitine into TMAO, which might raise cardiovascular risk; what this means is not yet well understood. Anticonvulsants such as valproic acid lower blood carnitine levels (NIH).
From regular food
This is a summary of public sources, not medical advice. If you have a health condition, are pregnant or take medication, talk to a doctor before taking a supplement.
Sources
- Carnitine — Fact Sheet for Health Professionals . NIH Office of Dietary Supplements, 2023.
- AIS Sports Supplement Framework — Group B . Australian Institute of Sport, 2026.
- ISSN exercise & sports nutrition review update: research & recommendations . International Society of Sports Nutrition, 2018.
Other supplements
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