In that humans naturally produce reactive oxygen species (ROS), which are necessary for a range of functions, including cell signaling, overproduction of ROS – which can occur as a result of high intensity exercise – may overwhelm the body’s antioxidant defenses and can lead to oxidative stress, a condition that is linked to an increased risk of various diseases including cancer, Alzheimer's, and cardiovascular disease. Glen Davison, from Aberystwyth University (Wales), and colleagues have found that dark chocolate containing 70% cocoa was associated with a blunting in oxidative stress after exercise. The researchers recruited 14 healthy men to participate in a study in which subjects consumed 100 grams of dark chocolate (70% cocoa), a control bar, or nothing. Two hours later, each subject bicycled for 2.5 hours at 60% of the maximal oxygen uptake level. The team found that the intake of the dark chocolate resulted in an increase in antioxidant status before the cycling, and reduced levels of F2-isoprostane, a marker of oxidative stress, one hour after the cycling had finished, as compared with the control bar. In addition, insulin levels were also increased before the trial and after cycling for men who consumed the dark chocolate, suggesting a better maintenance of plasma glucose concentration. There were no changes in markers of immune response, which is known to be affected by rigorous exercise.
Glen Davison, Robin Callister, Gary Williamson, Karen A. Cooper, Michael Gleeson. “The effect of acute pre-exercise dark chocolate consumption on plasma antioxidant status, oxidative stress and immunoendocrine responses to prolonged exercise.” European J Nutrition, 5 April 2011