There’s also generalized intermediate processes that respond to any physical stressor, including gastric issues, with modification of long term gene expression. This would mean that a gastric disorder would be incrementally adding to systemic stress levels and quite possibly changing the rate at which your body expresses genes for hormones and neurotransmitters, among other things that impact mental health. Edit: I’d cite but at this point the best I can do is say I read the article circa February 2020.