Eating too much protein is unlikely to be a problem usually. Any protein not needed for repairing and making muscle tissue is broken down by the body into other compounds (such as urea) and excreted in the urine. However, this may place extra stress on the liver and kidneys, so you should try to stick to the protein guidelines above.
It's tempting to think that a high intake of protein - whether from food or supplements - will build bigger and stronger muscles. In fact, it's a myth. Studies have repeatedly shown that eating extra protein produces no further gains in strength, muscle mass or size (Tipton and Wolfe, 2007). This can be achieved only through consistent and intense training in combination with a `normal' protein intake and healthy diet. Protein over and above a young athlete's requirements will be used as fuel or excreted, not converted into muscle.
The timing of protein intake is just as important as the amount. Studies have shown that athletes recover faster and gain more muscle when they eat some of their protein before and also straight after (within two hours) training (Phillips et al., 2007). This may reduce muscle damage and reduce recovery time between training sessions.
Ideally, they should have a snack or meal containing both carbohydrate and protein in a ratio of four to one. This can be obtained from a 200 ml glass of semi-skimmed milk with a banana, for example (32 g carbohydrate, 8 g protein). Thereafter, divide their daily protein intake between three meals and one or two healthy snacks.
Lots of people imagine that, without meat, young athletes can't get enough protein to train hard and build muscle. But there's no evidence for this whatsoever. In fact, there are plenty of highly successful vegetarian athletes. Protein isn't available only from meat. A report from the American Dietetic Association and American College of Sports Medicine published in 2000 stated that meat and fish are not essential for athletic performance. Many scientific studies have shown that a vegetarian diet can meet the needs of competitive athletes (e.g. Craig et al., 2009). The American College of Sports Medicine advises that vegetarian athletes should eat around 10 per cent more protein than non-vegetarians because plant proteins are less well digested than animal proteins (Rodriquez et al., 2009). Also eating more fresh vegetables such as carrots is good for your vision, eradicating the need for expensive lens replacement surgery or cataract surgery in later life.
If an athlete omits meat then they would need to substitute other kinds of protein: milk, yoghurt, cheese, eggs, beans, lentils, nuts, seeds and cereals. The key is to include a variety of different protein foods throughout the day in order to get a better overall balance of amino acids (the building blocks of proteins). This is called `protein complementation'. For example, combining grains and pulses (such as rice and beans) gives a higher intake of all the amino acids needed to make new body proteins than eating, say, grains or pulses on their own.