CYCLING PERFORMANCE

Protein is used to repair cell injuries (muscles particularly) from the microscopic trauma that occurs with exercise. It is NOT a good energy source, and serves that purpose only in malnourished states. Even in endurance activities such as the Tour De france, protein needs of 1.5 gms protein/kg body wt/day were easily met by a normal (read unsupplemented) diet that replaced the total Calories used each day.

All protein molecules are composed of building blocks called amino acids. Most protein digestion occurs in the small intestine where protein molecules are first split into their component amino acids which are then absorbed by the intestinal lining, transported via the circulatory system, and taken up by cells throughout the body. These amino acids are then used to rebuild cell proteins. Any excess protein in the diet is transformed (metabolised) into carbohydrates (gluconeogenesis) or fat. Protein itself is not stored in the body which means cell repair occurs from protein eaten that day or from amino acids released as protein is broken down elsewhere in the body.

http://www.cptips.com/protein.htm