Protein is essential for a growing teen because it helps build and maintain the tissues of the body. According to the American Heart Association, girls between the ages of 14 and 18 should eat 5 oz. of protein a day. One egg or 1 tbsp of peanut butter equals 1 oz.of protein, according to PBS Kids. A meat entree typically contains more protein. For instance, a small chicken breast or hamburger provides about 3 oz.

To a teenager, the idea of eating grains may call to mind images of the bran cereal that Grandma eats, but the grain food group includes bread, rice and pasta, too. A teenage girl should eat about 6 oz. of grains a day, and half of those should be whole grains. A cup of cereal or 1/2 cup of cooked pasta or rice provides one oz. of grains.Try to limit your teen's consumption of grains to no more than 6 oz. a day, because grains are filling. Overloading on them doesn't leave room for protein, fruits and vegetables.

Some teens avoid fruits and vegetables like the plague, but the nutrients in produce make them an essential part of any diet. Teenage girls should aim to eat at least 1-1/2 cups of fruit and 2-1/2 cups of vegetables per day, although she can eat as many vegetables as she likes. A whole apple, orange or banana is equal to about 1 cup. Juice doesn't count toward a serving of fruit unless it's made with 100 percent fruit juice. If your teen is a picky eater, offer creamy dips with fresh fruits and vegetables.

The dairy food group includes milk and milk products like cheese. Teenagers should eat about 3 cups of dairy foods per day. One and a half oz. of cheese -- a piece about the size of two dominoes -- is equivalent to 1 cup of dairy. Any type of cow's milk will suit the dairy requirements, but low-fat milk is the healthiest choice. A girl could satisfy this requirement by drinking 1 cup of milk at each meal. If your teen turns her nose up at milk, keep buttermilk and individual serving sizes of cottage cheese, yogurt and frozen custard in the fridge.