Protein is essential for growth, energy, and tissue repair. Athletic performance depends on muscle strength, and muscles are made of protein. Although athletes who are involved in strength and endurance training may need slightly more protein, it’s a mistake to think you can simply build up muscles by eating lots of protein. Exercise, not dietary protein, increases muscle mass. The amount of protein adolescents need varies at different stages of development. As a rule, boys and girls between ages 11 and 14 need half a gram per pound of body weight daily. Thus, a young teenager weighing 110 pounds needs about 50 g of protein a day. Between ages 15 and 18, the RDA drops slightly. As with all essential nutrients, common sense is the rule you don’t have to weigh every gram on a scale. Each gram of protein provides 4 calories the same as carbohydrates and protein should make up about 10% to 12% of each day’s calories. As a general rule, there are approximately 22 g of protein in 3 oz of meat, fish, or poultry. An 8-oz glass of milk contains about 8 g of protein. Carbohydrates, found in starches and sugars, get converted into the body's main fuel: the simple sugar glucose. Not all carbs are created equal, however. In planning meals, we want to push complex-carbohydrate foods and go easy on simple carbohydrates. Complex carbs provide sustained energy; that's why you often see marathon runners and other athletes downing big bowls of pasta before competing. As a bonus, many starches deliverfiber and assorted nutrients too. They are truly foods of substance: filling yet low in fat. A well-rounded diet based on the USDA guidelines should deliver sufficient amounts of all the essential vitamins and minerals. Adolescents tend to most often fall short of their daily quotas of calcium, iron, zinc, and vitamin D.