High protein diets carry a number of risks, especially to someone who is still growing. One serious risk is kidney damage. High protein consumption causes an increase in pressure in the glomeruli of the kidneys, which can cause kidney stones and chronic kidney disease. Proteins are also typically low in fiber, and fiber is known to be important to the health of the digestive tract as a cancer preventative. The digestion of protein creates a need for pH buffering in the blood, which causes the body to pull calcium from the bones; excess protein consumption, particularly during a growth spurt, could lead to prematurely weakened bones.
Another important thing to note is that not all proteins are alike. Many animal based proteins add saturated fats to the diet. Processed meats such as cold cuts have many preservatives and may present a cancer risk. Many brands of protein powder sold specifically for bodybuilders have recently been shown by Consumer Reports to be contaminated with dangerous amounts of heavy metals such as cadmium and lead. For young athletes, as for everyone else, the safest and best diet is one with a good variety and a balance among the food groups.