Effect of Nigella sativa supplementation on obesity indices: A systematic review and meta-analysis of randomized controlled trials

Background & objective(s): No meta-analysis is available on the effect of Nigella sativa (NS) on obesity indices. This systematic review and meta-analysis was conducted to systematically review the available Randomized Clinical Trials (RCTs) that examined the effects of NS on Body Weight (BW), Body Mass index (BMI), and Waist Circumference (WC) in adults. Methods: Relevant articles published up to January 2018 were searched through PubMed/Medline, SCOPUS, Cochrane Library, and Google Scholar databases, using relevant keywords. All RCTs that examined the effect of NS supplementation on BW, BMI, or WC were included. Results: Overall, thirteen RCTs, including 875 subjects (64% males) were included in this study. Combining effect sizes from ten studies, NS supplementation significantly reduced BW (Weighted Mean Differences (WMD): -1.76 kg, 95% CI: -3.34 to -0.17, I-2 = 87.4%), as compared to placebo. Subgroup analysis by the intervention type (I-2 = 0.0%), participants' gender (I-2 = 0.0%), and age (I-2 = 5.5%) removed between-study heterogeneity. A significant reduction was seen in BMI (WMD: -0.85 kg/m(2), 95% CI: -1.23, 0.46, I-2 = 70.6%) after NS supplementation than placebo among eleven trials. Subgroup analysis based on study duration (I-2 = 0.0%), participants' gender (females: I-2 = 0.0% & both genders: I-2 = 20.9%), an age (I-2 = 35.9%) disappeared the heterogeneity. However, no significant reduction was found in WC comparing NS supplementation to placebo (WMD: -4.04 cm, 95% CI: 11.37, 3.27, I-2 = 97.8%) in five studies. Conclusions: We find a significant effect of NS supplementation on BW and BMI in adults. However, the effect of NS supplementation on WC was not significant in this meta-analysis.