The weight loss supplement that promised to burn fat: L–Carnitine sounds like a perfect marketing dream. It exists in the body, participates in transferring fatty acids into the mitochondria, where they are used to produce energy, and therefore it is very easy to sell it as a "fat-burning supplement." Anyone seeking to lose weight quickly, get toned before the summer, or improve workout performance, might be convinced that adding capsules or a drink containing L–Carnitine will cause the body to break down more fat. However, human biology is far more complex than a slogan on a shelf.
The body produces carnitine on its own in the liver and kidneys, and also receives it from food, mainly from animal products. Its role is real and important, but this does not mean that an external excess will necessarily lead to increased fat burning. In a healthy person who does not suffer from a rare carnitine deficiency, it is not clear that a large supplement of the substance will lead to a significant change in body composition. Weight loss still depends mainly on caloric balance, exercise, sleep, muscle mass, and persistence over time.
In recent years, another, more interesting and troubling question has arisen regarding L–Carnitine: What happens to it in the gut. Gut bacteria can break down various nutritional components, including carnitine, and create trimethylamine from them. This substance reaches the liver, where it turns into TMAO.
In human studies, a link was found between high levels of TMAO and an increased risk of cardiovascular disease, heart attacks, strokes, and mortality. In animal studies, possible mechanisms of accelerated atherosclerosis were also observed. However, it is important to be precise: A link is not proof of full causality in every person, and the risk is also affected by diet, gut bacterial composition, underlying diseases, and cardiac risk factors.
Therefore, the problem is not the mere existence of carnitine in the body, nor is it natural food containing it. The problem is concentrated consumption as a supplement, sometimes in high doses, without a clear medical need and without monitoring. Anyone who is already at cardiac risk, suffers from high cholesterol, high blood pressure, diabetes, kidney disease, or a family history of early heart disease, should be especially careful about adding supplements that promise "fast toning" but have not proven significant and clear benefit for them.
What Actually Works for Weight Loss?
Even among healthy trainees, it is worth asking a simple question before purchasing: What exactly am I trying to achieve, and is there good evidence that this supplement will do so? If the goal is a reduction in fat percentage, the most effective way remains boring but true: A tailored diet, enough protein from food, resistance training, aerobic activity, and sleep. L–Carnitine is not a substitute for any of these.
Natural is not an insurance policy: Even a natural substance can be unnecessary, expensive, or problematic when consumed in high amounts and in a concentrated form. Anyone taking L–Carnitine due to a specific medical recommendation should act according to a doctor. Anyone buying it solely because of a promise of fat burning, should know that this promise is much weaker than the marketing surrounding it.
Dr. Itay Gal is a specialist in pediatrics, sports and aviation medicine, and the medical commentator for Maariv