Does supplementation with green tea extract improve insulin resistance in obese type 2 diabetics? A randomized, double-blind, and placebo-controlled clinical trial.

Abstract

Background: Green tea is one of the most popular beverages in the world. It is believed to have beneficial effects in the prevention and treatment of many diseases, one of which is type 2 diabetes. The aim of the study is to examine the effect of a decaffeinated green tea extract (GTE) providing a daily dose of 856 mg of epigallocatechin gallate (EGCG) on obese individuals with type 2 diabetes.

Materials and methods: The clinical trial was a randomized, double-blind, placebo-controlled clinical trial conducted from December 2007 through November 2008. The subjects were randomly assigned to either receive 1,500 mg of a decaffeinated GTE or placebo daily for 16 weeks. Sixty-eight of 80 subjects, ages 20-65 years with BMI > 25 kg/m2 and type 2 diabetes for more than one year, completed this study. Homeostasis model assessment for insulin resistance (HOMA-IR) was used as the major outcome measurement. At baseline and after 16 weeks of treatment, anthropometric measurements, fasting glucose, hemoglobin A1C percent (HbA1C), hormone peptides, and plasma lipoproteins were measured from both groups.

Results: No statistically significant differences were detected between the decaffeinated GTE and placebo groups in any measured variable. A statistically significant within-group 0.4-percent reduction in HbA1C (from 8.4 to 8.0%) was observed after GTE treatment compared to baseline. Within-group comparison also revealed that the GTE group had significant reductions in waist circumference (WC), HOMA-IR index, and insulin level, and a significant increase in the level of ghrelin. Within-group comparison of those in the placebo group showed a significant increase in the level of ghrelin.

Conclusions: This study found no statistical difference in any measured variable between the decaffeinated GTE and placebo groups; however, there were some statistically significant within-group changes detected. More research is required to determine whether a decaffeinated GTE standardized for EGCG content will provide any clinical benefits in obese individuals with type 2 diabetes. Clinical Trial Registration NO: NCT00567905.