Potential interaction between timing of infant complementary feeding and breastfeeding duration in determination of early childhood gut microbiota composition and BMI

Background: Introducing complementary foods other than breastmilk or formula acutely changes the infant gut microbiota composition. However, it is unknown whether the timing of introduction to complementary foods (early vs. late) in infancy is associated with early childhood gut microbiota and BMI, and if these associations depend on breastfeeding duration. Objective: Our primary objective was to investigate whether timing of infant complentary feeding with solid foods is associated with early childhood gut microbiota composition and BMI-z, and whether these associations differ by duration of breastfeeding. Methods: We used data from a Canadian pre-birth cohort followed till age 5 years. We examined timing of introduction to solid foods with the gut microbiota, determined by 16S rRNA gene sequencing of stool collected at 5 years of age, and age-and-sex specific BMI-z. We conducted analyses before and after stratifying by breastfeeding duration, and adjusted for delivery mode, gestational age and birth weight. Results: Of the 392 children in the analysis, 109 (27.8%) had early (≤4 months) solids. The association between early (vs later) solids and BMI-z at 5 years was modified by breastfeeding status at 4 months (P =.06). Among children breastfed >4 months, early (vs later) solids were associated with differential relative abundance of 6 bacterial taxa, including lower Roseburia, and 0.30 higher BMI-z (95% CI: 0.05, 0.55) at 5 years. In children breastfed <4 months, early solids were associated with differential relative abundance of 9 taxa, but not with child BMI-z. Conclusions: Early (vs. later) introduction to solid foods in infancy is associated with altered gut microbiota composition and BMI in early childhood, however these associations differ by duration of breastfeeding.