In an eight-week study in 38 women who exercised four times per week, there was no difference in weight loss between those who took L-carnitine and those who didn’t (24).

What’s more, five of the participants taking L-carnitine experienced nausea or diarrhea (24).

Another human study monitored L-carnitine’s effect on fat burning during a 90-minute stationary bicycle workout. Four weeks of taking supplements did not increase fat burning (28).