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I'm curious if there's any synthesis / study / general theory of this.
As my own datapoint, I've had pretty bad digestive issues, trouble eating, and ahedonia for a while. I recently got to do a natural experiment when I accidentally left my milk out. Since I've cut milk, I've felt much better (though not perfect) on all counts. So I'm probably lactose intolerant (though I never really noticed a correlation between my symptoms and milk consumption).
Probably worth checking if there are any easy fixes to your digestive issues if you have them.