A question I am often asked is whether it matters when a baby is weaned for the optimal development of the infant microbiome.

It turns out introducing solids at or before age 4 months significantly increases the risk of a child becoming overweight or obese later in childhood.

New research by Differding et al., (2020) suggests early weaning starting at 4 months or before is associated with a 30% higher risk of being overweight or obese (high Body Mass Index) in childhood, and a less diverse gut microbiome.

However, those children who were breastfed for more than 4 months, did not have a higher BMI at 5 years.

Breast milk is species-specific and is the ideal food for human babies. Breastfeeding is considered the gold standard for feeding and nutrition for all babies, and this research indicates it is protective against obesity.

Details of the research: 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.

Conclusion: "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."

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Scientific Reference:

Differding, M. K., Doyon, M., Bouchard, L., Perron, P., Guérin, R., Asselin, C., Massé, E., Hivert, M.-F. & Mueller, N. T. Potential interaction between timing of infant complementary feeding and breastfeeding duration in determination of early childhood gut microbiota composition and BMI. Pediatr Obes 9, e12642 (2020). https://onlinelibrary.wiley.com/doi/abs/10.1111/ij...