Green tea extract and catechol‐O‐methyltransferase (COMT) genotype modify fasting serum insulin and plasma adiponectin concentrations in a randomized controlled trial of overweight and obese postmenopausal women.
Authors: Dostal Allison , Samavat Hamed , Espejo Luis , Arikawa Andrea , Stendell‐Hollis Nicole R , Kurzer Mindy S 
Published: June 2021

BackgroundGreen tea consumption has been associated with favorable changes in body weight and obesity‐related hormones, though it is unknown if this is due to green tea polyphenols or caffeine.ObjectiveWe examined the impact of decaffeinated green tea extract (GTE) containing 843 mg (−)‐epigallocatechin‐3‐gallate (EGCG) on anthropometric variables, obesity‐associated hormones, and glucose homeostasis.MethodsThe Minnesota Green Tea Trial was a 12‐month randomized, double‐blind, placebo‐controlled clinical trial of 937 healthy postmenopausal women assigned to either GTE or placebo based on catechol‐O‐methyltransferase (COMT) genotype. This study was conducted in a subset of 237 overweight and obese participants (BMI ≥ 25 kg/m2).ResultsNo changes in energy intake, body weight, BMI, or waist circumference (WC) were observed over 12 months in women taking GTE (n=117) or placebo (n=120). No differences were seen in circulating leptin, ghrelin, adiponectin, or glucose concentrations at month 12. Participants randomized to GTE with baseline insulin ≥10 μIU/mL (n=23) showed a decrease in fasting serum insulin from baseline to month 12 (−1.43 ± 0.59 μIU/mL), while those randomized to placebo with baseline insulin ≥10 μIU/mL (n = 19) showed an increase in insulin over 12 months (0.55 ± 0.64 μIU/mL; P < 0.01). Participants with the homozygous high‐activity (G/G) form of COMT showed significantly lower adiponectin (5.97 ± 0.50 vs. 7.58 ± 0.53 μg/mL, P = 0.03) and increased insulin concentrations (7.63 ± 0.53 vs. 6.18 ± 0.36 μIU/mL, P = 0.02) at month 12 as compared to those with the low‐activity (A/A) genotype, regardless of treatment group.ConclusionsDecaffeinated 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 months. 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 reduction in adiponectin concentrations over time. This clinical trial was registered at http://www.clinicaltrials.gov as NCT00917735.Support or Funding InformationResearch reported in this publication was supported by the National Institutes of Health/National Cancer Institute grant R01 CA127236, Award Number T32CA132670 from the National Cancer Institute, the Department of Defense/U.S. Army Medical Research and Materiel Command Award Number W81XWH‐11‐1‐0013, the University of Minnesota Graduate School Doctoral Dissertation Fellowship, the University of Minnesota Agricultural Experiment Station Project Number MIN‐18‐103, and the National Center for Advancing Translational Sciences of the National Institutes of Health Award Number UL1TR000114. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health. The funding sources and study supplement provider did not contribute to the design or conduct of the study, nor to the writing or submission of this manuscript.