[hyeonwho4]

Human infant intestines in the ancestral environment are natively colonized by bifidobacterium infantis, which completely metabolizes oligosaccarides present in human breast milk and outputs highly acidic byproducts. This acid kills most other gut bacteria, allowing B. infantis to consist of 50% of the intenstinal microbiome in healthy infants [1]. Oligosaccarides cannot be metabolized by babies without gut bacteria, but human mothers produce more of them than most other mammals we know of, and the specific oligosaccarides present depend on maternal generics [4]. NICU infants untreated with B. infantis are 5x more likely to fall into sepis as a result of necrotizing enterocolitis[2,3], probably due to increased intestinal permeability to pathogens.

But B. infantis is coevolved for the digestion of human oligosaccarides, and those are specifically genetically coded for in human milk [4]. As a result, "vegan baby formula" or even baby formula without the correct oligosacarides could be a disaster for baby intestinal health, and even cow's milk has a different oligosaccaride profile, and we don't know how adaptable the gut microbes are.

[1] doi.org/10.1038/s41390-020-01350-0 [2] doi.org/10.1542/peds.2004-1463 [3] doi.org/10.1038/s41372-019-0443-5 [4] doi.org/10.1038/s41467-024-45209-y