Dark chocolate is high in powerful antioxidants called polyphenols that protect cells against free radicals, which are produced naturally during metabolism. Free radicals are highly reactive chemicals that cause damage to DNA, cell membranes, skeletal muscle proteins, and suppress the immune system. Antioxidants combine with free radicals and prevent their destructive effects.
Scientists from Loughborough University in Great Britain found that cyclists consuming 40 grams per day of dark chocolate for two weeks showed less oxidative stress, compared to athletes given low-cocoa chocolate. Athletes given dark chocolate also showed greater fatty acid mobilization during exercise. However, dark chocolate had no effect on cycling performance. Dark chocolate is a healthy food that protects the cells from oxidative stress. (International Journal Sports Nutrition Exercise Metabolism, 11: 113-123, 2011)