Most very low birth weight infants accumulate a nutrient deficit in hospital due to minimal nutrient reserves and elevated nutritional requirements which may contribute to poor outcome. Adding nutrients to human milk improves their nutritional status and growth, but it is unclear if adding bovine protein-based fortifiers as is the current standard of care has some unintended negative consequences to neonates. Infants will be randomized to have their feeds (mother's own milk or pasteurized donor breastmilk) nutrient enriched with a human milk-based fortifier or a bovine protein-based fortifier and will be followed in hospital to assess feeding tolerance, growth, gut inflammation, gut microbiome, and neonatal morbidity and mortality.