[rossdavidh]

True that, but it could be both cause and effect. There are reports that gut bacteria can induce depression, which benefits the bacteria because it sends more calorie-rich, highly processed food down the gullet (think ice cream binges when depressed). Not hard to believe that gut bacteria optimized for a particular kind of food could evolve the ability to induce their host to eat that food exclusively. It would have the side-benefit (for the bacteria) of reducing competition from other microbes that aren't optimized for that, by starving them out. Things aren't always just cause or effect, especially in biology.

[senfiaj]

Maybe. IMHO there is also a microbiome hype train in the recent years. Most of these microbiome studies aren't considering a lot confounding factors. Here is a paper: https://www.cell.com/cell/fulltext/S0092-8674(21)01231-9 that found only very little evidence for association between ASD and gut microbiome.