I absolutely love spicy food, and it’s never affected my gut. I was actually confused when I read about people getting the shits after a curry and wondered if it was a joke. I’ve had curries so hot it caused people to recoil into a coughing and sweating fit after they dipped their finger in and had a taste and I have one every other day. I feel the burning in my mouth, my face turns red, my forehead sweats, my esophagus feels weird, but (tmi I know lol) when I go to the toilet I’m completely fine. no gut pains either.
For me, some spices that involve oils or the seeds can give my gut a punch. For example, I like jalapeños for flavor, but too much and my gut doesn’t like it. Hotter peppers use less of the pepper for spice, so they don’t crank up the digestion. Some other spices don’t have any effect whatsoever, like dried red pepper can make my mouth burn but never upset the stomach.
I think most of it is what your body is used to, as eating more hot stuff makes it a lot less likely for my stomach to revolt about the jalepenos. But if I take a month off I’m rolling the dice.