As someone with gut issues from early childhood I can honestly say that looking at my diet, making long term changes to what I ate made a massive difference.
Sure, at times as a young adult I was fuelled by caffeine & nicotine, but generally my diet was probably not outrageously bad.
I also discovered that some food do unpleasant "things" to my insides. Peanuts for example & that is because I am mildly allergic.
When I developed ME, diet & gut candid overgrowth were considered to be potentially curative. It made no difference to ME symptoms. I have noticed that even fairly high stress makes virtually no difference to how my gut behaves.
If my "habits" change then thinking back will usually identify a cause - peanuts, pineapple, forgetting to eat fruit one day that kind of thing.
A bad gut can be extremely painful - the word discomfort doesn't cover it- being in pain all day, having your abdomen swell up so you increase by at least one dress size, needing to be near a loo just in case etc. are all perfectly reasonable concerns. Fix the gut issue and those worries disappear.
Plus, I have no doubt it is quite possible that by products of whatever is going on in the gut may well alter mood.
By all means deal with the psych issues if they don't resolve after one has dealt with the gut problems. Or are the gut problems just too difficult for 'em?
On another note - someone I was extremely close to died because they were so used to living with severe gut problems. Gut issues can cause very strong chest pain, especially if gas is trapped in the stomach. They didn't notice when they had a series of mini heart attacks until they dropped dead. Literally.
Time to stop this effing about guys. You'll kill people with this nonsense.