While human milk provides optimal nutrition for full-term infants, its nutrient density is inadequate for those born preterm. Formula made from bovine milk can provide higher levels of energy and protein but lacks many of the bioactive components found in human milk, including the ‘‘personalised’’ components found only in the mother’s own milk (MOM). The aim of this study was to compare the effects of bovine-derived human milk fortifiers (BHMF) versus human-derived human milk fortifiers (H2MF) on gut microbiome development, oxidative stress, and gut inflammation in human-milk-fed very low birth weight preterm neonates. This study was a randomised controlled trial. Very low birth weight infants were recruited into the study and randomised to receive standard BHMF or H2MF during the intervention period. Results showed that the type of milk fortifier (bovine versus human) had minimal impact on the gut microbiome, whereas the source of human milk (mother versus donor) was strongly associated with microbiome composition. Authors conclude that their findings do not provide a clear biological basis for the clinical impact of H2MF but emphasise the importance of mothers using their own milk to feed their preterm infants.