And what happens if teen athletes don't eat enough? Their bodies are less likely to achieve peak performance and could break down rather than build up muscles. Teen athletes who don't take in enough calories every day won't be as strong and as fast as they could be. And calorie restriction could lead to growth problems and other serious health risks for teen athletes.

Since teen athletes need extra fuel, it's usually a bad idea for them to diet. Athletes in sports where weight is important — such as football, wrestling, swimming, or gymnastics — might feel pressure to gain weight, but they need to weigh that choice with the possible negative side effects mentioned above. If a coach, gym teacher, or teammate says that you need to go on a diet, talk to your doctor first or visit a dietitian who specializes in teen athletes. If a health professional you trust agrees that it's safe to diet, he or she can work with you to develop a plan that allows you to perform your best and gain weight.

Athletes need slightly more protein than less-active teens, but most teen athletes get plenty of protein through regular healthy eating. It's a myth that athletes need a huge daily intake of protein to build large, strong muscles. Muscle growth comes from regular training and hard work — not popping pills. And taking in too much protein can actually harm the body, causing dehydration, calcium loss, and  kidney problems.