Effects of Kefir Consumption on Cardiometabolic Risk Factors: A Systematic Review and Meta-analysis of Randomized Controlled Trials

Background: Fermentation of lactose in milk by bacteria and yeasts naturally present in kefir grains produces a beverage that has been suggested to have cardiovascular benefits. This systematic review and meta-analysis of randomized controlled trials (RCTs) aimed to evaluate the effects of this kefir beverage on cardiometabolic risk factors. Methods: Literature search utilised PubMed, Scopus, ISI Web of Science, and Google Scholar for articles published from inception until June 2021. Cardiometabolic risk indices extracted included insulin and insulin resistance (HOMA_IR), total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), fasting blood sugar (FBS), haemoglobin A1c (HbA1c) and body weight (BW). In total, six RCTs (314 subjects) were selected for the meta-analysis. Inverse-variance weighted mean difference (WMD) with a 95% confidence interval (CI) was calculated for the mean changes in TC, TG, HDL-C, LDL-C, FBS, HbA1c and BW compared to baseline. A random effects model was used to estimate the pooled WMD. Results: Kefir intake significantly reduced fasting insulin (WMD: -3.69 micro-IU/mL,95% CI: -6.30 to -1.07, p = 0.006, I² = 0.0%) and HOMA-IR (WMD: -2.56, 95% CI: -3.82 to -1.30, p<0.001, I² = 19.4%). No effect on TC (p = 0.088), TG (p = 0.824), HDL-C (p = 0.491), LDL-C (p = 0.910), FBS (p = 0.267), HbA1c (p = 0.339) or body weight (p = 0.439) were found for kefir treatment. Conclusion: Kefir has a beneficial effect in decreasing insulin resistance; however, no effect was seen on BW, FBS, HbA1C, and lipid profile.