Effects of green coffee extract on fasting blood glucose, insulin concentration and homeostatic model assessment of insulin resistance (HOMA-IR): A systematic review and meta-analysis of interventional studies

Many studies have investigated the relationship between coffee and diabetes. Evaluation of the current evidence on the effect of coffee intake on diabetes is critical. Therefore, we aimed to investigate the potential association between green coffee extract (GCE) and fasting blood glucose (FBG), insulin and homeostatic model assessment of insulin resistance (HOMA-IR) by pooling together the results from clinical trials. PubMed, Scopus and Google Scholar were searched for experimental studies which have been published up to December 2018. Randomized controlled trials (RCTs) that investigated the effect of GCE supplementation on FBG, insulin and HOMA-IR in adults were included for final analysis. A total of six articles were included in the meta-analysis. Results revealed that GCE supplementation reduced FBG level (SMD: -0.32, 95% CI - 0.59 to - 0.05, P = 0.02) but had no effect on insulin levels (SMD: -0.22, 95% CI -0.53 to 0.09, P = 0.159). Although analysis showed that GCE supplementation cannot change the HOMA-IR status (SMD: -0.30, 95% CI -0.73 to 0.13, P = 0.172), after stratified studies by GCE dosage (< 400 mg/day versus > 400 mg/day) there was a significant decrease in HOMA-IR status in a dose greater than 400 mg. These findings suggest that GCE intake might be associated with FBG improvement.