The Effect of Dark Chocolate on Metabolism and Performance in Trained Cyclists at Simulated Altitude

Dark chocolate is rich in flavonoids, bioactive micronutrients that increase the bioavailability of nitric oxide as well as decrease the rate in which nitric oxide is removed from the body. Through increasing the bioavailability of nitric oxide (NO) to bodily tissues, the tissues are better able to utilize oxygen, synthesize energy, and utilize glucose from the blood. In addition to increasing the bioavailability of nitric oxide, the flavonoids in dark chocolate also have antioxidant properties, which reduce oxidative stress and inflammation in the muscle. These anti-inflammatory and antioxidant properties have been show to alleviate muscle damage after intense exercise and improve recovery. These factors are of benefit for endurance athletes through improving performance and enhancing recovery from exercise.

Studies investigating the effects of dark chocolate on exercise performance are few, and thus more research is needed to strengthen evidence for or against dark chocolate for endurance exercise performance. Dark chocolate has been shown to improve time trial performance in some studies due to the increased bioavailability of NO while showing no effect on performance in others, displaying an inconsistency in the literature. Although oxidative stress has been studied, no studies to date have investigated the effects of dark chocolate on the product of this stress, muscle damage. To measure muscular damage, we will be assessing muscular pain and force recovery.

Dark chocolate also contains caffeine and theobromine (73mg and 883mg per 100g serving, respectively) Caffeine and theobromine have been shown to have beneficial effects on exercise performance through increasing fatty acid mobilization and slowing the onset of fatigue.

Finally, carbohydrates with a low glycemic index are better than those with a high glycemic index for stimulating fat usage at the muscle and therefore have potential to improve endurance exercise performance because endurance performance is limited by carbohydrate availability in the muscle. Dark chocolate has a glycemic index of 23, meaning it has very little effect on blood sugar, and thus results in lower insulin release than other carbohydrates (insulin inhibits fat usage at the muscle). Thus, dark chocolate may have performance enhancing effects through the mechanisms of nitric oxide, caffeine, and theobromine while providing carbohydrates that cause a reduced spike in blood sugar compared to other carbohydrate sources often used by athletes such as energy bars and gels.

In the current study the investigators are testing the effects of dark chocolate on cycling at altitude because some of the most important cycling races (e.g. Tour de France) involve cycling through mountain stages. Altitude places an extra challenge on cyclist because of the lower partial pressure of oxygen in the atmosphere. A food such as chocolate, which is proposed to enhance oxygen deliver to muscle may be ideal for exercise at altitude.