> Studies that have measured changes in endogenous lactase activity after an intervention period consistently show a lack of enzyme induction, suggesting that lactose intake does not affect an individual's lactase activity. Although these studies are scarce and have relatively few subjects, data from cross-sectional studies support the theory of purely genetic regulation
That's interesting, and thank you for bringing it up.
What I was speculating about though, and what may be more relevant for the (Science) article, also includes things along the lines of a microbe manipulating the host gene expression to improve its living conditions.
For instance a species that derives energy by fermenting glucose to lactate might under certain conditions have better benefit from that piece of metabolism if it can also make the host act as a sink for the product.
Again, not sure if that particular example is real or documented, but the idea has some consequences for the sort of adaptations and connections one might find.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6669050/
> Studies that have measured changes in endogenous lactase activity after an intervention period consistently show a lack of enzyme induction, suggesting that lactose intake does not affect an individual's lactase activity. Although these studies are scarce and have relatively few subjects, data from cross-sectional studies support the theory of purely genetic regulation