L-Carnitine is technically an amino acid derivative, but its often grouped with peptides because of its performance-enhancing effects. It helps transport fatty acids into cells to be burned for energy, making it a favorite for fat-burning and endurance support. Unlike stimulants that spike your energy then crash you later, L-Carnitine works by optimizing how your body uses fat as fuel. That makes it a smart addition to any weight loss or athletic performance plan.