Green tea extract and catechol-O-methyltransferase genotype modify fasting serum insulin and plasma adiponectin concentrations in a randomized controlled trial of overweight and obese postmenopausal women

Background: Green tea consumption has been associated with favorable changes in body weight and obesity-related hormones, although it is not known whether these changes result from green tea polyphenols or caffeine. Objective: We examined the impact of decaffeinated green tea extract (GTE) containing 843 mg of (2)-epigallocatechin-3-gallate on anthropometric variables, obesity-associated hormones, and glucose homeostasis. Methods: TheMinnesota Green Tea Trialwas a 12-mo randomized, double-blind, placebo-controlled clinical trial of 937 healthy postmenopausal women assigned to either decaffeinated GTE (1315mg total catechins/d) or a placebo, stratified by catechol-O-methyltransferase (COMT) genotype. This study was conducted in a subset of 237 overweight and obese participants [body mass index (BMI) ≥25 kg/m²]. Results: No changes in energy intake, bodyweight, BMI, orwaist circumference (WC) were observed over 12mo inwomen taking GTE (n = 117) or placebo (n = 120). No differences were seen in circulating leptin, ghrelin, adiponectin, or glucose concentrations at month 12. Participants randomly assigned to GTEwith baseline insulin ≥10 μIU/mL (n = 23) had a decrease in fasting seruminsulin frombaseline tomonth 12 (-1.4±60.59 μIU/mL), whereas those randomly assigned to placebowith baseline insulin ≥10 μIU/mL (n = 19) had an increase in insulin over 12 mo (0.55 ± 0.64 μIU/mL, P < 0.01). Participants with the homozygous high-activity (G/G) form of COMT had significantly lower adiponectin (5.97 ± 0.50 compared with 7.58 ± 0.53 μg/mL, P = 0.03) and greater insulin concentrations (7.63 ± 0.53 compared with 6.18 ± 0.36 μIU/mL, P = 0.02) at month 12 compared with those with the low-activity (A/A) genotype, regardless of treatment group. Conclusions: Decaffeinated GTE was not associated with reductions in body weight, BMI, or WC and did not alter energy intake or mean hormone concentrations in healthy postmenopausal women over 12 mo. GTE decreased fasting insulin concentrations in those with elevated baseline fasting concentrations. The high-activity form of the COMT enzyme may be associated with elevations in insulin and a reduction in adiponectin concentrations over time. This trial was registered at http://www.clinicaltrials.gov as NCT00917735.