It is pretty clear that digestion varies dramatically from person to person, and from moment to moment for the same person. You hit upon two major things in you

It is pretty clear that digestion varies dramatically from person to person, and from moment to moment for the same person. You hit upon two major things in your question; what flora are in your gut, and how the rest of your body is. Anecdotally I've noticed I can change my stomach on purpose by what I eat, and rebalance the flora. For example I used to eat Tums all the time to deal with acid indigestion. Then I did a 3 day fast at the suggestion of my mother in law, and found I was free of indigestion for months after that. Now whenever I find myself getting heartburn more than a couple times I do a fast and it clears up for awhile. There is increasing evidence the balance of flora also contributes to how you process food, and can contribute to greater development of fat when out of whack.