Submitted to: European Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 28, 2012
Publication Date: August 1, 2012
Citation: Stote, K.S., Clevidence, B.A., Novotny Dura, J., Henderson, T.R., Radecki, S.V., Baer, D.J. 2012. Effect of cocoa and green tea on biomarkers of glucose regulation, oxidative stress, inflammation and hemostasis in obese adults at risk for insulin resistance. European Journal of Clinical Nutrition. 66:1153-1159. Interpretive Summary: Insulin resistance is a risk factor for type 2 diabetes and cardiovascular disease. Lifestyle strategies that include dietary modification, such as consumption of a plant-based diet, are well recognized in disease prevention and may improve insulin resistance. Several components of a plant-based diet may contribute to its beneficial health effects, but there has been much speculation that plant polyphenols may play a role. Cocoa and green tea are both dietary sources of polyphenols, specifically flavanols and the flavan-3-ols subclass. Our study investigated whether cocoa flavanols can affect glucose metabolism in adults at risk of insulin resistance. In addition, we compared the effects of green tea and a high flavanol containing cocoa on glucose metabolism. As part of a randomized crossover design, 20 subjects (10 men, 10 women) each consumed a controlled diet at weight maintenance along with 5 treatment beverages: 1) high-flavanol cocoa (1300 mg flavanols), 2) medium-flavanol cocoa (385 mg flavanols), 3) low-flavanol cocoa (190 mg flavanols), 4) control cocoa (40 mg flavanols), and 5) green tea (matched for the catechin content of the high-dose cocoa). Each subject consumed the treatments with both breakfast and the evening meal for 5 days. On the sixth day, the subjects underwent an oral glucose tolerance test. Biomarkers measured were glucose, insulin, triglycerides, insulin resistance, and insulin sensitivity. Twelve, 7, and 1 subjects were identified as being insulin resistant, insulin sensitive, and diabetic, respectively. Glucose and insulin concentrations did not change significantly after consumption of the cocoa treatments. However, green tea compared with the high flavanol cocoa lowered glucose and elicited a lower insulin response in insulin-sensitive but not insulin-resistant subjects. Cocoa and green tea did not affect triglycerides, or other values. Consumption of green tea compared with the high flavanol cocoa improves glucose tolerance in insulin sensitive obese adults. These findings will be important to scientists who are interested in the health effects of green tea and cocoa consumption.
Technical Abstract: Flavanols may provide protection against insulin resistance, but little is known about the amounts and types of flavanols that may be efficacious. This study was designed to determine whether cocoa flavanols, over a range of intakes, improve biomarkers of glucose regulation, inflammation and hemostasis in obese adults at risk for insulin resistance. As an adjunct, green tea and cocoa flavanols were compared for their ability to modulate these biomarkers. In a randomized crossover design, 20 adults consumed a controlled diet for 5 days along with four cocoa beverages containing 30–900'mg flavanol per day, or tea matched to a cocoa beverage for monomeric flavanol content. Cocoa beverages produced no significant changes in glucose, insulin, total area under the concentration–time curve (AUC) for glucose or total insulin AUC. As the dose of cocoa flavanols increased, total 8-isoprostane concentrations were lowered (linear contrast, P=0.02), as were C-reactive protein (CRP) concentrations (linear contrast, P=0.01). The relationship between cocoa flavanol levels and interleukin-6 (IL-6) concentrations was quadratic, suggesting that a maximum effective dose was achieved (quadratic contrast, P=0.01). There were no significant effects on measured indices of glucose regulation, nor on those of total 8-isoprostane, CRP and IL-6 concentrations, when cocoa and green tea were compared. However, relative to cocoa, green tea lowered fibrinogen concentrations (P=0.0003). 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.