OBJECTIVE:Our objective was to perform a systematic review and meta-analysis on randomized controlled trials (RCTs) assessing the effect of flaxseed supplementation on serum adiponectin and leptin concentration. METHODS:Electronic searches were performed in PubMed, Scopus, Web of Science, and Google Scholar up to May 2019 without any restriction. All RCTs that reported the effect of flaxseed supplementation on circulating adiponectin and leptin concentration were included. A random-effects model was used to pool calculated effect sizes. RESULTS:Nine RCTs (11 arms) were eligible to be included. Our analysis showed that flaxseed supplementation did not significantly affect adiponectin (weighted mean difference [WMD]: 0.15 μg/ml; 95% CI [-0.16, 0.47], p = .34) and leptin (WMD: 0.47 ng/ml; 95% CI [-3.10, 4.06], p = .79) concentration in comparison with control. Furthermore, subgroup analysis revealed that effects remained nonsignificant in all subgroups of trial duration, flaxseed type, and health status of participants. The pooled effect size was also robust and remained nonsignificant in the sensitivity analysis. CONCLUSION:Flaxseed supplementation had no significant effect on adiponectin and leptin levels in adults. However, future well-designed trials are still needed to confirm these results.