Does carnitine burn fat?

Short answer

Not body fat. Pooling 37 trials, body weight fell 1.21 kg more, but body fat percentage did not differ. Carnitine built up in muscle only when taken with 160 g of carbs a day.

Does carnitine burn fat?
'More carnitine → fat into the cell's power plants → more fat burned' — does this formula hold?
Carnitine carries fat into the energy factories inside your cells (mitochondria). So a common belief is that taking more as a supplement burns more fat. We checked this formula step by step.
Does taking it load your muscles?
Blood levels rose, but muscle levels stayed the same
After taking 6 g a day for 14 days, carnitine in the blood went up. But carnitine in muscle stayed the same, and the amount of fat burned during exercise did not differ. Muscle already had enough carnitine to burn fat.
Getting it into muscle took carbs
Only with 160 g a day did it rise 21%
In a study of 8 people, carnitine entered muscle only when insulin was raised. When 14 people took 2 g of carnitine with 80 g of carbs twice a day for 24 weeks, muscle carnitine rose 21%. The carbs alone come to 160 g, about 640 kcal, a day.
So did they lose weight?
They didn't lose; they gained less
12 people ate 80 g of carbs twice a day for 12 weeks. The 6 who took carbs alone gained 1.9 kg of body weight and 1.8 kg of fat; the 6 who also took carnitine did not change. Carnitine blocked the gain from the extra calories but did not remove fat.
What about taking it with exercise?
8 weeks of carnitine and walking left fat unchanged
36 people took 4 g of carnitine a day or a placebo for 8 weeks while walking 30 minutes, 4 days a week. Body weight and body fat did not change, and the groups did not differ. 5 people in the carnitine group quit because of nausea or diarrhea.
Pooled studies show just over 1 kg
Body fat percentage did not change
An analysis that pooled 37 trials (2,292 people) found the carnitine groups lost on average 1.21 kg more body weight. Body fat percentage did not differ. An analysis of 911 people found 1.33 kg, and the gap shrank the longer people took it.
Instead, TMAO rose 10-fold
A substance involved in fatty buildup in blood vessels
When 20 people took 1.5 g a day for 24 weeks, TMAO in their blood rose 10-fold. TMAO is involved in the process of fatty buildup in artery walls. Over that time, inflammation and blood fat levels did not change.
Bottom line: the fat-burning effect is just over 1 kg
The formula breaks at the 'loads your muscles' step
Carnitine did not build up in muscle unless taken with 160 g of carbs a day. Pooling 37 trials, the weight difference was 1.21 kg, and body fat percentage stayed the same. Carnitine is best seen as a small extra in weight loss, at most.