Muscle tissue is made from protein.
Protein is responsible for repairing the damage you do to your muscles during training and making them stronger and larger. If size is what you want, you should be getting 1 1.5 grams of protein per pound of bodyweight. That is why protein supplementation is so important. Most bodybuilders get at least half of their daily intake from protein supplementation. Today s protein powders, meal replacements, and protein bars have protein sources far superior to regular food.