Faecal microbiota and Fat Free Mass Index in 2 to 3 year old well-nourished Australian children.

Background Alterations in microbiota composition are proposed to be causally related to the development of overweight and obesity while maturation of the gut microbiota has been shown to be related to childhood growth. However, while there has been a focus on the association between microbiota and body size in recent literature, the association with body composition is poorly characterised in humans. Method This study utilises previously reported data to explore the association between faecal microbiota composition and body composition in a cohort of 36 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 OTU belonging to the Ruminococcaceae family (Rho = 0.822, p < 0.001, pFDR = 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 microbiota may influence growth and body composition in early life through the modulation of fat free mass accrual, particularly in males.