Training stimulates muscle growth, and to maximize your efforts in the gym your body needs a sufficient amount of energy and enough raw materials to get the full benefit from your exercise program. Providing that energy and raw materials is the role of nutrition. It means knowing how much of what kinds of food to eat for the best possible results given your goals and body composition. Proper diet also supports your immune system, enhances recovery between workouts, and improves overall skin quality and internal organ function.