Weight loss: what really works (and false promises)

No supplement melts fat away. Weight loss relies on one single, unavoidable point: burning more calories than you consume. From there, certain supplements help a little at the margins—and others are mostly marketing. Let's sort it out, backed by studies.

The real lever: the caloric deficit

Before talking about supplements, the essential point: your calorie balance is what decides. The priority is therefore to know your needs, then create a moderate deficit while keeping enough protein so you don't melt away muscle at the same time as fat.

What helps a little: caffeine

Caffeine is one of the rare supplements whose benefits during exercise are well proven: it improves endurance and strength, and above all it reduces the perception of effort—you therefore train a little harder, which helps burn calories. On the "burner" side, the direct effect remains modest: a study on a green tea-caffeine mixture showed better weight maintenance via thermogenesis and fat oxidation, but we are talking about a boost, not a solution.

To be dosed with caution: around 3 mg per kg of weight is enough for the benefits, while high doses (beyond ~6 mg/kg) mainly increase side effects—palpitations and sleep disorders at the top of the list.

What protects your muscles: protein

In a caloric deficit, the risk is losing muscle in addition to fat. This is where a high protein intake matters: it preserves muscle mass during weight loss and better curbs appetite. Whey is nothing like a burner, but it is a practical way to reach those proteins without blowing up your calories—exactly what you need when you are eating less.

The false promise: L-carnitine

L-carnitine is the grand classic of "fat burners". The sales pitch seems logical: it transports fatty acids to the mitochondria to be burned. Except that this real biochemical role does not mean that taking it makes you lose weight. In our studies, L-carnitine has mostly been tested in medical contexts (cancer, dialysis, coronary heart disease), not as a weight loss aid in healthy people.

Even more telling: a controlled trial showed that 2 g per day did not even improve fatigue in patients—including when they were genuinely deficient. In other words, for the general public's physique, evidence of a slimming effect is lacking. It is not dangerous, but it is not the shortcut that advertising makes people believe.

In summary

The best "slimming pill" therefore remains a well-constructed plate. Track your daily intake with our food diary to stay in your deficit without depriving yourself at random.

The underlined mentions open the study from which the figure comes. The rest of the work on these three supplements is listed on their sheets — caffeine, whey, L-carnitine — each with its summary. Informative content, which does not replace medical advice.