The gut microbiota differ in exclusively breastfed and formula-fed US infants and are associated with growth status

Evidence regarding the effects of infant feeding type (exclusive breastfeeding vs. exclusive formula-feeding) on the gut microbiota and how it impacts infant growth status is limited. The primary objective is to compare gut microbiota by feeding type and characterize the associations between gut microbiota and infant growth status. Stool samples from healthy, full-term infants (4-5 months old) who were either exclusively breastfed (BF) or exclusively formula-fed (FF) in Denver, Colorado, USA were collected and fecal 16S rRNA gene-based profiling was conducted. Length and weight were measured at the time of stool collection. Length- (LAZ) and weight-for-age z-scores (WAZ), and weight-for-length z-scores (WLZ) were calculated based on the WHO standards. Associations between gut microbial taxa and anthropometric Z-scores were assessed by Spearman’s rank correlation test. 115 infants (BF n=54; FF n=61) were included in this study. Feeding type (BF vs. FF) was the most significant tested variable on gut microbiota composition (P < 1 x 10-⁶), followed by mode of delivery and race. Significant differences were observed in alpha diversity, beta diversity, and relative abundances of individual taxa between BF and FF. BF infants had lower alpha diversity than FF infants. Abundances of Bifidobacterium and Lactobacillus were greater in the breastfeeding group. Formula-fed infants had a higher relative abundance of unclassified Ruminococcaceae (P<0.001), which was associated with a higher WAZ (p<0.001) and LAZ (p<0.01). Lactobacillus was inversely associated with WAZ (p<0.05). Feeding type is a main driver of gut microbiota differences in infants. The gut microbiota differences based on feeding type (exclusive breast- or formula-feeding) were associated with observed differences in growth status.