Effects of Dietary Interventions on Gut Microbiome in Overweight or Obese Adults: A Systematic Review of Randomized Controlled Trials

Background: It has been shown that gut microbiota dysbiosis may induce intestinal permeability, and systemic inflammation, leading to metabolic dysregulation. Furthermore, it has been implicated in the etiology of obesity. Dietary intake is known to affect the gut microbiota. These RCTs suggested that different dietary interventions may exhibit different effects on the composition of gut microbiota in overweight or obese individuals.Objectives: This systematic review aimed to determine the effect of dietary intervention on the gut microbiota profiles in overweight or obese adults. The primary outcome of this systematic review is alpha-beta diversity and its changes at the species level.Materials and Methods: This systematic review followed the PRISMA guidelines and was registered in the PROSPERO database with registration number CRD42022298891. A systematic search was conducted through the databases PubMed, MEDLINE, CINAHL, and Scopus literature using the terms: “gut microbiota”,“microbiome”,“overweight”,“obesity”, “insulin sensitivity”,“insulin resistance”,“blood glucose”,“randomized controlled trial”. After screening abstracts and full texts, 18 articles were extracted by two authors.Results: Among the 18 RCT studies, dietary intervention gave an impact on gut microbiota alpha diversity changes in four studies. However, 7 studies showed no significant changes or differences compared to the placebo group. Beta diversity analysis was reported in 7 among 11 studies that performed alpha diversity analysis. Significant changes were found in food nutrients group (fiber supplementation) studies conducted over 8-12 weeks period. Seven more studies did not report any analysis of variance in either alpha or beta diversity. Changes in the composition of gut microbiota could be observed in dietary pattern interventions and resulting in improved metabolic status, except in the fried meat group diet. Interventions with food groups, food nutrients, and probiotics did not change the composition of gut microbiota.Conclusion: The effects of dietary interventions on alpha-beta diversity are inconsistent, but rather showed more consistent effects on the changes in microbiota composition, especially in dietary pattern interventions.  