Effects of dietary supplementation with the green tea polyphenol epigallocatechin-3-gallate on insulin resistance and associated metabolic risk factors: randomized controlled trial

Abstract

Animal evidence indicates that green tea may modulate insulin sensitivity, with epigallocatechin-3-gallate (EGCG) proposed as a likely health-promoting component. The purpose of this study was to investigate the effect of dietary supplementation with EGCG on insulin resistance and associated metabolic risk factors in man. Overweight or obese male subjects, aged 40-65 years, were randomly assigned to take 400 mg capsules of EGCG (n 46) or the placebo lactose (n 42), twice daily for 8 weeks. Oral glucose tolerance testing and measurement of metabolic risk factors (BMI, waist circumference, percentage body fat, blood pressure, total cholesterol, LDL-cholesterol, HDL-cholesterol, TAG) was conducted pre- and post-intervention. Mood was evaluated weekly using the University of Wales Institute of Science and Technology mood adjective checklist. EGCG treatment had no effect on insulin sensitivity, insulin secretion or glucose tolerance but did reduce diastolic blood pressure (mean change: placebo - 0.058 (se 0.75) mmHg; EGCG - 2.68 (se 0.72) mmHg; P = 0.014). No significant change in the other metabolic risk factors was observed. The EGCG group also reported feeling in a more positive mood than the placebo group across the intervention period (mean score for hedonic tone: EGCG, 29.11 (se 0.44); placebo, 27.84 (se 0.46); P = 0.048). In conclusion, regular intake of EGCG had no effect on insulin resistance but did result in a modest reduction in diastolic blood pressure. This antihypertensive effect may contribute to some of the cardiovascular benefits associated with habitual green tea consumption. EGCG treatment also had a positive effect on mood. Further studies are needed to confirm the findings and investigate their mechanistic basis.

Figures

Fig. 1

Flow of participants through the phases of the study. EGCG, epigallocatechin-3-gallate.

Fig. 2

Mean blood pressure change after 8 weeks of dietary supplementation (■, placebo, n 42; , EGCG, n 46). Mixed model analysis of covariance was used with baseline included as a covariate, subject as a random effect and treatment group as a fixed effect. Values are least square means with their standard errors depicted by vertical bars. Values were significantly different: *P=0·096, †P=0·014.

Fig. 3

Effect of dietary supplementation on mood, as measured by the University of Wales Institute of Science and Technology (UWIST) mood adjective checklist (■, placebo, n 42; , EGCG, n 46). UWIST data were analysed by mixed model repeated measures analysis of covariance, with baseline included as a covariate, subject as a random effect, treatment group as a fixed effect and week number as a repeated measures term. Values are least square means with their standard errors depicted by vertical bars. No baseline differences (P≤0·05) were detected between the two groups. Values were significantly different: *P=0·056, †P=0·048.