Gut Microbiota Is Significantly Impacted by Feeding Mode and Associated With Growth Status in Exclusively Breastfed and Formula-Fed US Infants

OBJECTIVES: Growth and shifts of gut microbiota during infancy are greatly influenced by diet. Our objective is to both compare and characterize the gut microbiota and growth status according to feeding type in healthy U.S. infants. METHODS: Infants (4–5 months old) who were either exclusively breastfed or exclusively formula-fed infants were recruited from the metro Denver area. Stool samples along with the length and weight measurements, were collected from these infants, and fecal 16S rRNA gene-based profiling was conducted. Alpha diversity indices measured for the gut microbiota were tested using the Mann-Whitney statistic. Differences in microbiota composition (beta-diversity) were assessed by permutational ANOVA, using Aitchison dissimilarity scores. Individual taxa differing between groups were identified using the ANOVA-like Differential Expression tool (ALDEx2) to centered-log ratio transformed count data. Associations between gut microbial taxa and anthropometric Z scores were assessed by Spearman's rank correlation test. Length- and weight-for-age z-scores, and weight/length z-scores (LAZ, WAZ, WLZ) were assessed. RESULTS: 115 infants (breastfed n = 54; formula-fed n = 61) between the ages of 4 and 5 months were studies. Formula-fed infants had higher WAZ and WLZ than breastfed infants (p < 0.05). Although not statistically significant, LAZ was also higher in formula-fed compared to breastfed infants. (p = 0.14). Significant differences were observed in both the alpha and beta diversity and composition of fecal microbiota between breastfed and formula-fed infants. The breastfed cohort had lower alpha diversity than the formula-fed cohort. Bifidobacterium was the most abundant bacteria among all participants. Abundances of Bifidobacterium and Lactobacillus were greater in the breastfed group compared to the formula-fed group. Formula-fed infants tended to have a higher relative abundance of the unclassified Ruminococcaceae, which was associated with a higher WAZ (p < 0.001) and LAZ (p < 0.01), while Lactobacillus was associated with a statistically higher WAZ (p < 0.05). CONCLUSIONS: The gut microbiota differences by feeding mode may contribute to differences in growth between breastfed and formula-fed infants. FUNDING SOURCES: NIDDK, AHA, NPB, NCBA.