Eat sufficient amounts of protein, the best source of proteins include:
Red meat: Beef, pork, lamb, venison, bison, etc.
Fish: Tuna, salmon, swordfish, bass, trout, mackerel, etc.
Poultry breast: Chicken, turkey, duck, etc.
Dairy: Milk, cheese, cottage cheese, yogurt, etc.
Whey: Protein shakes...