To answer this another way…athletes clearly need more protein than non-athletes. The literature is clear about this.┬á
Allow me to quote a colleague that I respect who really knows his stuff:
How much depends on what you are doing and what your goals are.┬á Exercise causes a small uptick in protein requirements to be nitrogen neutral.┬á But exercise often stimulates an increase in caloric consumption so, assuming those calories come with some protein, it doesn’t require a big change.
The big issue is with weight loss. Bodybuilders, wrestlers, or just people trying to lose weight—all of these people need a calorie deficiency.┬á A high protein diet can maximize lean muscle mass retention during weight loss, but with decreasing effect beyond a certain point.┬á I recall a study where they tested up to 1.5 g protein/lb lean for a fairly severe diet and found that even at this very high protein level, there was a small benefit in terms of reducing lean muscle loss.
So if a bodybuilder is trying to cut for a show, then he/she may be eating at a caloric deficit for 4 months, trying to retain as much lean as is humanly possible.┬á As a result, they get nearly all of their calories from protein because it is simpler and because trying to fit 300 g of protein into a 1500 cal/day diet leaves only 300 extra calories to come from fat and carbohydrates.