Childhood Obesity and Firmicutes/Bacteroidetes Ratio in the Gut Microbiota: A Systematic Review

BACKGROUND: The aim of the present study was to undertake a systematic review exploring the relationship between childhood obesity and fecal microorganisms, to answer the following question: "Are Firmicutes and Bacteroidetes a significant risk indicator/factor for obesity in children?" The main search terms were "child" and "obesity" together with "gut microbiota" (PubMed: 2005-2017). The minimal requirements for inclusion were the evaluation of gut microbiota composition and BMI in children between 0 and 13 years of age. METHODS: Assessed articles were carefully classified according to a predetermined criterion, and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) were considered. Seven articles were critically appraised and used as a basis for conclusions. RESULTS: Three studies showed a positive association between Bacteroides fragilis and obesity. In addition, a high value of evidence indicated that a decrease in the Bacteroidetes phylum and in Bacteroides/Prevotella groups was related to high BMI. For the Firmicutes phylum, one high-quality study highlighted that it was positively correlated with weight gain. With regard to Firmicutes species, Clostridium leptum, Eubacterium hallii, and Lactobacillus spp. indicated adipose tissue storage, while Clostridium difficile and the Staphylococcus genus were correlated with low BMI. Despite the fact that only one study did not perform real-time polymerase chain reaction to quantify the microorganisms, its results corroborated those of the studies that did. CONCLUSIONS: Changes in Firmicutes and Bacteroidetes phyla/species levels might in fact be significant indicators/factors for childhood obesity. However, given the small number of articles appraising these entire phyla and the heterogeneity among the species assessed, further well-designed studies are required to improve the knowledge.