Since nutrition and exercise go hand in hand, it is important to have protein apart of your meals and snacks. Aging and dieting for weight loss can result in losing muscle as well as fat. To help prevent muscle loss, your plate should include leucine-rich protein sources. What is leucine you might ask? Leucine is an essential amino acid that can help you burn fat while keeping your learn muscle tissue intact. The human body does not produce leucine, so it is important to include sources in your diet. Some good sources of leucine include: fish, tofu, egg whites, and chicken.