Male-specific Association Between Fat-Free Mass Index and Fecal Microbiota in 2-to 3-Year-Old Australian Children

Objectives:Maturation of the gut microbiota has been shown to influence childhood growth, whereas alterations in microbiota composition are proposed to be causally related to the development of overweight and obesity. The objective of this study is to explore the association between microbiota profile, body size, and body composition in young children.Methods:Fecal microbiota was examined by 16S rRNA gene sequencing, whereas body composition was assessed using the deuterium oxide dilution technique in a cohort of 37 well-nourished 2- to 3-year-old Australian children.Results:Microbiota composition (weighted UniFrac distance) was shown to be significantly associated with FFMI (fat-free mass index) z score (P=0.027, adonis) in boys but not girls. In boys, FFMI z score was significantly correlated with the relative abundance of an OUT (Operational Taxonomic Unit) belonging to the Ruminococcaceae family (Rho=0.822, P<0.001, pFDR (false discovery rate adjusted P value)=0.002, n=18). At a FDR <0.2, FFMI z score in boys was positively associated with the relative abundance of OTU related to Dorea formicigenerans and Faecalibacterium prausnitzii and negatively correlated to an OTU related to Bacteroides cellulosilyticus.Conclusions:These results suggest that previously reported associations between microbiota composition and body size may be driven by an association with fat-free mass, particularly in males.