I don't have awful stomach issues but sometimes I have bathroom inconsistencies and bloating. Nothing severe came up but I have mild reactions to Beef, Chicken, Sweet Potatoes, Broccoli, Raspberries, Tuna and moderate to Mackerel (never eat anyway so who cares lol), Brewer's Yeast (I do AWFUL with beer) and a few other things.
I also have Candida/dysbiosis which is causing Leaky Gut.
I eat Beef and Chicken every single day for years on end and A LOT of it each day, so this could be why I have stomach issues and carry my excess fat there. Really lean and muscular everywhere else so it's annoying.