For me, I know that insoluble fiber is a big problem, especially concentrated like in dried fruit - raisins, for example. Grapes and cherries are hard for me to tolerate, and now I'm experimenting with peeling my fruit (not grapes; that would be silly) like apples and pears.I am sensitive to gluten, especially first thing in the morning on an empty stomach, and caffeine. I gave up caffeine, but I will eat gluten foods later in the day when there's food in my stomach already.I don't tolerate garlic and onions, although when cooked, they're slightly less offensive. I use leeks in cooking now because they don't affect me the way onions do.And I don't tolerate beer or red wine well (and by beer, I mean the good dark stuff, which is what I drink).Forgot to mention spicy foods, especially Indian. And popcorn, which is my worst weakness (although I've discovered it's also a matter of quantity). Sometimes we go to a movie and I have popcorn and then we go out for Indian food, and I SO suffer the next day.I find that dairy ISN'T a problem for me.Interestingly, I'm on day 9 of a 10-day detox/cleanse diet where I've eaten no sweeteners, dairy, soy, gluten, corn, peanut products, vinegar, alcohol, caffeine, etc. Meat is also not allowed, but I'm vegetarian so don't eat it anyway. I can only eat low-carb fruits and vegetables, beans, whole gluten-free grains, and a little oil and salt (thank goodness). And I'm drinking a shake twice a day and taking probiotics, extra fiber (benefiber) and supplements that are part of the cleanse. My digestion has not improved one fraction (I also have GERD). I thought that maybe by eating really clean for ten days that I might notice an improvement. Everything is exactly the same. Huh.