Below is a pretty good article on veggie athletes, click the link for the full article, or below are a few excerpts. Nice to see that lack of 'protein combining' myth, and have them spell out that getting 15% of your calories from protein is quite easy.
Science of Sport: Can Endurance Runners Be Vegetarians?
Many meat-eating athletes wonder whether a switch to a vegetarian diet might provide a performance boost, and there are logical reasons for such thinking. First, vegetarian diets tend to be high-carbohydrate regimens, which should lead to optimal glycogen storage in muscles. At the lofty intensities required for high-level training and serious competition, carbohydrate is the primary source of energy; when muscle-carbohydrate (glycogen) levels are too low, athletes experience fatigue and tend to perform poorly (1). Thus, a vegetarian diet may function as an "insurance policy" against insipid intramuscular carbohydrate storage andunderachievement in races.
In addition, it is possible that vegetarian eating might enhance the recovery process following tough workouts and competitions. The reasoning goes this way: High-intensity or prolonged effort generates increased levels of "free radicals" within an athlete's body, potentially enhancing the breakdown of cell membranes, including the membranes which wrap around muscle cells (2). An athlete's own physiological systems can synthesize antioxidant enzymes to stem this free-radical onslaught, but an additional line of defense is provided via the consumption of antioxidant nutrients. Vegetarian diets revolve around fruits, vegetables, and whole grains - the kinds of food which are high in antioxidants. Thus, vegetarian eating may do a better job of protecting muscle cells during hard training, compared with dietary plans which are more biased toward meats.
Protein is another concern for vegetarians, since plant foods can be considerably lower in protein, compared with meat. Research indicates that endurance athletes probably need to take in approximately 1.2 to 1.4 grams of protein per kilogram of body weight per day - and that strength athletes might need as much 1.4 to 1.8 grams per kilogram daily. While such intakes might seem rather expansive, they are actually fairly easy to meet when athletes - including vegetarians and meat-eaters - simply keep their protein intakes at around 15 percent of total calories (14). As Dr. David Nieman points out in an excellent review article (15), even totally vegan athletes can enjoy optimal protein intake by emphasizing the consumption of protein-rich plant foods, including legumes (beans and peas), nuts, seeds, and whole-grain products.
So what is the bottom line about vegetarian eating and athletic performance? As Dr. Nieman points out, the available evidence indicates that a vegetarian diet has neither a demonstrably positive nor significantly negative effect on physical capacity. Although vegetarian diets are definitely "endurance-athletes' diets," in the sense that they are high in carbohydrate, usually adequate in protein, and low in fat, it is possible for meat-eaters to consume just as much carbohydrate as vegetarians do; when this happens, meat-lovers and vegetarians perform in similar fashion during endurance activities. There has been some concern that vegetarian female athletes are at increased risk for menstrual dysfunction, but Nieman indicates that low energy intake, not vegetarian eating per se, is the actual culprit in this area. Finally, vegetarian athletes do not seem to be at higher risk for impaired nutrient status, either in terms of protein or various minerals. As Dr. Nieman concludes, "…a varied and well-planned vegetarian diet is compatible with successful athletic endeavor."