Notably, we found an expansion of Verrucomicrobia driven by A. muciniphila, which has been implicated in human diseases such as obesity,63,64 multiple sclerosis,65,66 and seizures.67A. muciniphila metabolizes host-derived mucus as a nutrient source,68 consistent with the increase in luminal mucin proteins and digestive enzymes we observed in ChAT+-activated mice. Here, CHAT is linked to obesity due to melanocortin 4 receptor deficiency.