The effect of acute pre–exercise dark chocolate consumption on plasma antioxidant status, oxidative stress and immunoendocrine responses to prolonged exercise
Journal Title (Medline/Pubmed accepted abbreviation):  Eur. J. Nutr..
Year: 2012
Volume: 51
Page numbers: 69-79

Summary of background and research design:

Background: Foods that are high in antioxidants have the ability to prevent exercise–induced oxidative stress. Dark chocolate, which contains high amount of polyphenols, is among those foods.

Hypothesis: An acute dose of dark chocolate will reduce the exercise–induced oxidative stress response to prolonged (<2 hr) exercise.

Subjects: Fourteen males, age 22 ± 1 y completed the study.

Experimental Design: randomized, counterbalanced, cross–over study. Researchers were blinded to the identity of the treatments, but sensory differences between the chocolate types prevented subjects from being blinded to treatment identity.

Baseline– no food consumed
Dark chocolate– 100 g of Nestlé Noir chocolate, 70% cocoa containing a combination of polyphenols Control chocolate– 71 g chocolate with 0% cocoa liquor (therefore no polyphenols) (For reference, a regular size Hershey’s chocolate bar is 43 g).

Protocol:: The participants arrived at the laboratory in the morning after an overnight fast and consumed one of the 3 treatments. Then, 2 hrs later, they cycled at 60% of their maximal oxygen uptake for 2.5 hrs. Blood was collected immediately before and after exercise then 1 hr post–exercise. Respiratory gases were collected every 30 min. Heart rate and ratings of perceived exertion were acquired every 15 min. Blood was analyzed for antioxidant capacity, neutrophil function, polyphenol content, F2–isoprostane concentration (a marker of oxidative stress), hormones including cortisol, cytokines including IL–6, and metabolites including non–esterified fatty acids.

Summary of research findings:
  • The physiological demand of exercise, plasma volume, heart rate, and rating of perceived exertion were all similar between trials.
  • Only dark chocolate increased the concentration of epicatechin (an antioxidant) in the plasma (maximum concentration = 0.08 mg/L before exercise).
  • There was a small but statistically significant exercise–induced increase in plasma F2 isoprostanes (a marker of lipid peroxidation) with the control chocolate and no treatment, but not with dark chocolate. This suggests that dark chocolate mitigated exercise–induced oxidative stress, however it is unknown if this small effect was physiologically relevant.
  • Plasma insulin was significantly greater pre–exercise with the dark chocolate compared to the other treatments.
  • There was a trend towards higher levels of non–esterified fatty acid concentrations in the plasma with dark chocolate, suggesting that there may have been a higher amount of fat metabolism.
  • Plasma glucose concentrations were significantly higher post–exercise compared to the other treatments (4.3 ± 0.4 mM for dark chocolate vs. 3.9 ± 0.1 for control chocolate and 4.0 ± 0.1 for no chocolate). In other words, there was a smaller amount of blood sugar fluctuation in response to exercise.
  • No significant differences were observed for cortisol, adrenocorticotropic hormone (ACTH), IL–6, or lactate between trials.

Key practice applications: Consumption of dark chocolate 2 hrs before exercise leads to an increase in antioxidant status and an attenuation of exercise–induced oxidative stress. It also led to an increase in insulin and glucose concentrations before and after exercise, respectively. However, it is unknown how this affects performance.

Limitations: It is unknown what components of the dark chocolate led to these observations. For example, the dark chocolate contained more caffeine than the control chocolate (104 mg vs. 17 mg). Because different types of chocolates vary in composition, we don’t know which types/brands of chocolate will provide similar effects.

Key search terms for this article (5-7 terms): chocolate, antioxidants, oxidative stress, polyphenols, catechins

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