a1 Unilever Corporate Research, Colworth Park, Sharnbrook, Bedfordshire MK44 1LQ, UK
a2 MRC-Human Nutrition Research, Elsie Widdowson Laboratory, Fulbourn Road, Cambridge CB1 9NL, UK
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.
(Received February 15 2008)
(Revised June 05 2008)
(Accepted June 23 2008)
(Online publication August 19 2008)
Abbreviations: EGCG, epigallocatechin-3-gallate; HOMAIR, homeostasis model assessment of insulin resistance; OGTT, oral glucose tolerance test; UWIST, University of Wales Institute of Science and Technology