The branched chain fatty acids (BCFAs) are a family of saturated fatty acids found in specific locations, such as the skin sebaceous gland and the moll’s gland of the eye. BCFAs are thought to play an important role in maintaining membrane fluidity under oxidative conditions. But what is the nutritional significance of these fatty acids? Professor Tom Brenna looks at the vernix, the waxy coating on the skin of newborns. Unique to humans, the vernix contains high concentrations of BCFAs, and is sloughed off and swallowed during the third trimester of development. In normal term infants, BCFAs form a protective biofilm on the lumen of the digestive tract, providing a unique niche that fosters the development of a healthy gut microbiota.The absence of BCFAs in pre-term infants with necrotinizing enterocolitis (NEC) underscores the critical importance of BCFAs. How do BCFAs exert their protective effects? Brenna reviews the in vitro and in vivo data illustrating how BCFAs can alter the activity and motility of harmful pathogens and simultaneously support the growth of beneficial strains. These remarkable findings encourage further research into the potential of BCFAs to support gastrointestinal health and the human gut microbiome during infancy and beyond.