Effects of Green Tea Consumption on Body Weight and Markers of Insulin Resistance: A Meta-Analysis


Video Presentation


Introduction: Obesity and diabetes are ongoing health concerns in the United States, especially in rural Appalachia. Commercially available green tea (Camellia sinensis) products may promote weight loss and insulin sensitivity as indicated by change in body weight and insulin-resistance markers. Green tea could provide potential benefit in the adjunctive management of obesity and diabetes. Obesity and diabetes could lead to comorbidities such as cardiovascular diseases. Osteopathic physicians consider aspects of lifestyle that impact disease risk. Addition of green tea is a simple dietary change that may reduce the risk of chronic diseases associated with 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 body weight (kg) and/or Homeostatic Model Assessment of 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, ClinicalTrials.gov, CINAHL, TRIP, Cochrane Central of Controlled Trials and Science Direct Health and Life Sciences were searched for parallel-designed and double-blinded RCTs published between 2010 and 2020 that examined the effect of green tea on anthropometric and insulin resistance markers. 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: 13 studies were included for meta-analysis. 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 both body weight and HOMA-IR index with mean effect size of -1.54% (95% CI -2.54%, -0.53%, p=0.003) and –19.75% (95% CI -35.11%, -4.39%, p=0.01), respectively. Studies that were included in our meta-analysis were widely varied in patient selection, dosing, dosing strategy, and outcome measurements, as indicated by the funnel plots.

Conclusion: We show a modest impact of green tea consumption on percentage change in body weight and HOMA-IR index. The differences in patient population, dose and dosing strategy suggest broader applicability of the results. Limitation of studies include lack of detail documentation about participants’ demographics. Biological sex, ethnicity, and pre-existing conditions could have an impact due to genetic polymorphism. Addition of 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. More research is needed to assess the utility of green tea consumption in management of obesity and diabetes. Future research opportunities include conducting large RCTs to address the public health concern of obesity, diabetes and preventive medicine.