Dietary Fiber and Metabolic Syndrome: A Meta-Analysis and Review of Related Mechanisms

(1) Background: Dietary fiber intake may provide beneficial effects on the components of metabolic syndrome (MetS); however, observational studies reported inconsistent results for the relationship between dietary fiber intake and MetS risk. We conducted a meta-analysis to quantify previous observational studies and a narrative review to summarize mechanisms involved in the potential relationship. (2) Methods: The literature was searched on PubMed and Web of Science until 28 November 2017. A random-effects model was used to calculate the summary risk estimates. Eleven cross-sectional studies and three cohort studies were included in the meta-analysis. Results from the original studies were reported as odds ratios (ORs) or relative ratios (RRs) of the MetS associated with different levels of dietary fiber intake, and the ORs/RRs comparing the highest with lowest categories of the intake were pooled. (3) Results: For the cross-sectional studies, the pooled OR was 0.70 (95% confidence interval (CI): 0.61-0.82) with evidence of high heterogeneity (I-2 = 74.4%, p < 0.001) and publication bias (p for Egger's test < 0.001). After removing four studies, results remained significant (OR = 0.67, 95% CI: 0.58-0.78) and the heterogeneity was largely reduced (I-2 = 32.4%, p = 0.181). For the cohort studies, the pooled RR was 0.86 (95% CI: 0.70-1.06). (4) Conclusion: Although the meta-analysis suggests an inverse association between dietary fiber intake and risk of MetS, and the association was supported by a wide range of mechanism studies, the findings are limited by insufficient cohort data. More prospective studies are needed to further verify the association between dietary fiber intake and the risk of MetS.