On the other hand, the daily flavanol supplements did not affect glucose metabolism, according to findings published in the European Journal of Clinical Nutrition.
The health benefits of polyphenols from cocoa and green tea have been gathering increasing column inches in the national media. To date studies have reported potential benefits for cardiovascular health, skin health, and even brain health.
The majority of science into the potential benefits of cocoa have revolved around cardiovascular benefits of the flavanols (also known as flavan-3-ols or catechins), and particularly the monomeric flavanol (-)epicatechin.
Green tea contains between 30 and 40 per cent of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3 and 10 per cent. Oolong tea is semi-fermented tea and is somewhere between green and black tea. The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC).
For the new study, scientists from the US Department of Agriculture’s Agricultural Research Service in Beltsville, MD, recruited 20 adults to participate in their randomized crossover study. The volunteers consumed a control diet with four cocoa beverages containing between 30 and 900 mg flavanol per day, or tea matched to a cocoa beverage for monomeric flavanol content for five days.
Results showed that no significant changes in glucose or insulin after consuming the cocoa beverages, but a dose-dependent decrease in 8-isoprostane (a marker of oxidative stress) and C-reactive protein (CRP - a marker of inflammation) levels were observed.
However, no significant effects were observed for measures of glucose or insulin regulation.
“Short-term intake of cocoa and green tea flavanols does not appear to improve glucose metabolism; they do affect selected markers of one or more measures of oxidative stress, inflammation or hemostasis in obese adults at risk for insulin resistance,” concluded the researchers.
Source: European Journal of Clinical Nutrition
Published online ahead of print, doi:10.1038/ejcn.2012.101
“Effect of cocoa and green tea on biomarkers of glucose regulation, oxidative stress, inflammation and hemostasis in obese adults at risk for insulin resistance”
Authors: K.S. Stote, B.A. Clevidence, J.A. Novotny, T. Henderson, S.V. Radecki, D.J. Baer