Despite many years of widespread international recommendations to support exclusive breastfeeding for the first six months of life, common hospital feeding and birthing practices do not coincide with the necessary steps to support exclusive breastfeeding. These common hospital practices can lead to the infant receiving formula in the first weeks of life despite mothers' dedication to exclusively breastfeed. Consequently, these practices play a role in the alarmingly high rate of formula-feeding worldwide. Formula-feeding has been shown to alter the infant gut microbiome in favor of proinflammatory taxa and increase gut permeability and bacterial load. Furthermore, several studies have found that formula-feeding increases the risk of obesity in later childhood. While research has demonstrated differences in the intestinal microbiome and body growth between exclusively breast versus formula-fed infants, very little is known about the effects of introducing formula to breastfed infants either briefly or long term on these outcomes. Understanding the relationships between mixed-feeding practices and infant health outcomes is complicated by the lack of clarity in the definition of mixed-feeding as well as the terminology used to describe this type of feeding in the literature. In this commentary, we highlight the need for hospitals to embrace the 10 steps of the Baby Friendly Hospital Initiative developed by UNICEF and the WHO for successful breastfeeding. We present a paucity of studies that have focused on the effects of introducing formula to breastfed infants on the gut microbiome, gut health, growth, and body composition. We make the case for the need to conduct well-designed studies on mixed-feeding before we can truly answer the question: how does brief or long-term use of formula influence the health benefits of exclusive breastfeeding?
Keywords: Baby Friendly Hospital Initiative; Bifidobacterium; body composition; breastfeeding; formula-feeding; human milk oligosaccharides; lactation; microbiome.