Acute L Carnitine Supplementation Does Not Improve CrossFit Performance: A Randomized, Double Blind, Placebo Controlled Crossover Study When to Take L Carnitine for Weight Loss & Maximize Results L Carnitine is not a magic fat burner It won't melt fat, build muscle, or replace hard work. The only thing it burns is your money Stick to the basics Should I use L Carnitine on rest days or just before workouts?