Efficacy of Green Tea Consumption on Reducing Body Mass Index and Insulin Resistance: A Meta‐Analysis

Abstract

Introduction Obesity and diabetes are ongoing public health concerns in the United States, especially in rural communities. Obesity is a leading cause of many conditions such as cardiovascular diseases and diabetes. Diabetes, specifically Type 2 Diabetes Mellitus (T2DM), is a leading cause of many conditions such as heart disease and vision problems. Commercially available green tea (Camellia sinensis) products may promote weight loss and insulin sensitivity as indicated by change in Body Mass Index (BMI) and insulin-resistance markers, which could provide potential benefit in the adjunctive management of obesity and diabetes. We conducted a meta-analysis on recent randomized controlled trials (RCTs) to test the hypothesis that consumption of green tea (GT) or green tea extract (GTE) for over four weeks can lead to a decrease in BMI and/or Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) index. Our study results will provide updated guidance on dietary recommendations and offer insight into effect sizes translatable to the general population. Methods Electronic databases including PubMed were searched for parallel-designed and double-blinded RCTs published between 2010 and 2020 that examined the effect of GT and GTE on BMI and/or HOMA-IR Index. Two authors independently reviewed articles for inclusion with differences resolved by consensus. Three authors independently assessed studies to assign risk of bias scores. Heterogeneity of studies was evaluated through use of forest plots and the I2 statistic using RevMan5 software. When necessary, data of varying measurement units were synthesized by meta-analysis. Results Eleven studies involving over 800 subjects were included. Daily doses of green tea ranged from 379 mg standardized extract to 20 mg green tea solids. Duration of interventions ranged from 4 to 48 weeks. Preliminary analysis indicates a statistically significant (p<0.05) percentage change in BMI and HOMA-IR index with mean effect sizes of –2.29% (95% CI –4.45%, -0.13%, p=0.04) and –19.75% (95% CI -35.11%, -4.39%, p=0.01), respectively. Most included studies had unknown or high risk of bias. Conclusions Included studies were widely varied in patient selection, dosing, dosing strategy, and outcome measurements. However, these differences suggest broader applicability of the results. Adding green tea may be an accessible, inexpensive and well-tolerated dietary change that may reduce the risk of chronic diseases associated with obesity and diabetes. Future research opportunities include conducting large RCTs to address the public health concern of obesity, diabetes and preventive medicine.