Sorry if this seems like a dumb question: How long does it take for you to notice your body's negative response to a particular food? I'm asking because I had tacos for the first time in several months yesterday... yes, non-primal tacos with crunchy corn shells. I was very hungry and they were delicious. I'm not going to pretend they weren't. HOWEVER, I had heartburn that started immediately after dinner and lasted for many hours. The pain was all in the belly, which is where I tend to get heartburn (not in the throat). It sucked. It made me never want to eat tacos again. (I know, I know: I should have made a shell-less taco salad.)

I'm assuming this is my body telling me that I can no longer eat corn taco shells, even rarely. But then again, sometimes the reaction isn't immediate. Say you have an episode of diarrhea one morning. Do you assume that's from whatever you had from dinner the night before? Or could it be from lunch? How do you establish the link between a particular negative reaction and a particular food you'd eaten, so you know what not to eat again?