How L Carnitine Helps Turn Fat Into Energy (Without Stimulants) Should I use L Carnitine on rest days or just before workouts? Supplements don't replace the workbut they can support it L Carnitine helps your body turn fat into usable energy, so you can push harder and recover better. Consistency first. Supplements second. Results L Carnitine for Fat Loss: Why Most Supplements Fail (and What Actually PEScience Does L Carnitine Work for Weight Loss? What the Science Says Carnitine: the claims and why it may not work