Burn fat. Keep muscle. Perform better., L Carnitine helps your body turn fat into fuelso your workouts actually work. Carnitine: the claims and why it may not work L Carnitine: Benefits, Uses, and Side Effects Lifespan Research Institute If you are like a lot of people, you may have never heard of carnitine but this important nutrient is critical for our body's ability to optimally burn fat required for energy.