L-Leucine can be a valuable tool in not only muscle building but can also play a critical role in weight loss. L-Leucine acts in a unique way: it can help burn fat without burning muscle. That’s a bit of a head scratcher because aminos are responsible for getting nutrients to the individual cells to burn, L-Leucine seems to be different; they found that L-Leucine actually spares the muscle proteins, leaving them to help build and increase muscle gain and mass.