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Breastfeeding & Risk for Overweight in Infants

Effects on infant gut microbiome a probable mediating factor

by Bianca Garilli, ND, IFMCP

The Global Breastfeeding Collective (GBC), co-led by UNICEF and WHO, has a mission to rally political, legal, financial, and public support for breastfeeding, which will benefit mothers, children, and society. Seven key priorities have been set forth by the GBC to increase the rate of breastfeeding globally; their most recent data from 2017 evaluated 194 nations and found that, “only 40 percent of children younger than six months are breastfed exclusively (given nothing but breastmilk) and only 23 countries have exclusive breastfeeding rates above 60 percent”.1 Looked at from the other side of the coin, this means a full 60% of children younger than six months are being partially to fully fed via breastmilk substitutes, typically in the form of infant formula.

When compared to breastfeeding, formula-feeding has been associated with a variety of negative effects in the infant/child including lower intelligence, atopy, type 1 and type 2 diabetes, and childhood obesity.2-4 Studies have indicated that the presence vs. absence of breastfeeding has a significant impact on the critical early development period, with more recent evidence demonstrating that the breastfeeding vs. formula  health outcomes may be mediated in part by differential effects on the composition of the gut microbiome.4-5

To better understand the relationship between breastfeeding, the infant gut microbiota, and the risk of overweight during infancy, a study that included 1,087 infants (507 girls; 580 boys) was carried out utilizing the prospective Canadian Healthy Infant Longitudinal Development (CHILD) pregnancy cohort.5 Feeding methods were reported by mothers and documented from hospital records, and fecal microbiota samples at time periods 3-4 months and/or 12 months were characterized by 16S ribosomal RNA sequencing.5 Risk for overweight was defined as an infant weight-for-length ratio exceeding the 85th percentile.5

At the 3-month mark, it was found that infants who were exclusively formula fed experienced:5

  • Increased risk for overweight
  • Higher overall richness/diversity of gut microbiota
  • Enrichment of the Lachnospiraceae bacteria family

A subset of infants who were briefly supplemented with formula as neonates but were then subsequently, exclusively breastfed were found to have a lower relative abundance of Bifidobacteriaceae and higher relative abundance of Enterobacteriaceae at the 3-4 month timeframe.5 This short exposure to formula and change in microbiota composition was not found to influence their risk of overweight at 12 months.5

The 6-month time point represents a period when breastfeeding mothers may choose to supplement with formula and/or introduce foods to the infant. These feeding methods/practices at 6 months of age influenced the microbiota composition of the infant at 12 months in the following ways:5

  • The gut microbe profile in infants receiving formula supplementation and only partially breastfed was found to be similar to the gut microbe profile of non-breastfed infants in that there was a higher diversity and quantity of Bacteroidaceae
  • The gut microbe profile in infants who were introduced to infant foods without concurrent introduction of formula was found to be similar to the gut microbe profile found in infants who had been exclusively breastfed in that there was a lower diversity and quantity of Bifidobacteriaceae and Veillonellaceae.

Finally, the authors found that the infant gut microbiota profiles at 3 months were more strongly associated with overweight risk than the microbiota profiles at 12 months.5

Why is this Clinically Relevant?

  • Breastfeeding continues to be the best method of infant feeding for a variety of reasons including a reduction in risk of various health conditions2-4
  • Formula feeding produces a distinct gut microbial profile from breastfeeding, and exclusive formula feeding is associated with higher risk for overweight in the infant5
  • Introduction of complementary foods was not associated with a similar increased risk of overweight5
  • The 3- to 6-month marks are sensitive developmental time periods, where feeding methods may highly influence the composition of gut microbiota and subsequent health outcomes at 12 months and possibly longer5
  • While “breast is best”, the breastmilk composition is directly correlated with the mother’s nutritional status, underscoring the importance of healthful nutrition and targeted supplementation where appropriate to address common nutrient gaps (e.g. vitamin D, calcium, omega-3s, etc.)

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  1. WHO. Babies and mothers worldwide failed by lack of investment in breastfeeding. Accessed July 5, 2018.
  2. Stevens EE, Patric TE, Pickler R. A history of infant feeding. J Perinat Educ. 2009;18(2):32–39.
  3. Rollins NC, Bhandari N, Hajeebhoy N, et al. Why invest, and what it will take to improve breastfeeding practices? Lancet. 2016;387(10017):491-504.
  4. Koletzko B, von Kries R, Closa R, et al. Can infant feeding choices modulate later obesity risk? Am J Clin Nutr. 2009;89(5):1502S-1508S.
  5. Forbes JD, Azad MB, Vehling L, et al. Association of exposure to formula in the hospital and subsequent infant feeding practices with gut microbiota and risk of overweight in the first year of life. JAMA Pediatr. 2018:e181161.


Bianca Garilli, ND, IFMCP is a former US Marine turned Naturopathic Doctor (ND). Dr. Garilli works in private practice in Northern California and consults with naturopathic and Functional Medicine leaders, including the Institute for Functional Medicine and Metagenics. She is passionate about optimizing health and wellness in individuals, families, companies, and communities—one lifestyle change at a time. Dr. Garilli has been on staff at the University of California, Irvine, Susan Samueli Center for Integrative Medicine and is faculty at Hawthorn University. She is the creator of the Military and Veteran Health Initiative and is the current Past-President of the Children’s Heart Foundation, CA Chapter.

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