Effects of Bifidobacterium infantis M-63 on gut environment and bowel function during weaning: RCT

BACKGROUND: Weaning involves rapid shifts in the gut microbiota, bowel irregularities, and increased infection risks. This exploratory, hypothesis‐generating study examined whether daily supplementation with Bifidobacterium longum subsp. infantis M‐63 (M‐63) may influence bowel function, the gut environment, and general health during weaning. METHODS: In a randomized, double‐blind, placebo‐controlled trial, 100 healthy infants and toddlers (5 months to under 3 years) received M‐63 (5 billion CFU) or placebo for eight weeks. Stool habits, fecal microbiota, and short‐chain fatty acids (SCFAs) were assessed. Cold‐like symptoms and medication use were recorded. Exploratory subgroup analyses considered breastfeeding status, age (<1.5 years), and the presence of siblings. RESULTS: M‐63 supplementation was associated with more days of normal stools and a trend toward fewer diarrhea episodes. Subgroup analyses revealed that breastfed children showed increased B. infantis abundance. In contrast, non‐breastfed children exhibited higher fecal SCFA levels. Children <1.5 years and those with siblings showed trends toward fewer cold‐like symptoms and reduced antibiotic use. No intervention‐related adverse events occurred. CONCLUSIONS: This exploratory trial suggests M‐63 may be associated with modest improvements in gastrointestinal outcomes and selected systemic health‐related measures during weaning. These findings should be interpreted cautiously and require confirmation in adequately powered trials. IMPACT: Daily administration of B. infantis M‐63 was associated with potential improvements in bowel habits among infants. In breastfed children, supplementation with B. infantis M‐63 was associated with an observed increase in the relative abundance of B. infantis, alongside a trend toward greater bifidobacterial diversity. In non‐breastfed children, B. infantis M‐63 was associated with modestly elevated levels of fecal metabolites, including short‐chain fatty acids. Exploratory findings suggest that supplementation with B. infantis M‐63 during weaning may modulate the gut environment and may be associated with immune‐related measures, but confirmation in larger, rigorously designed trials is needed.