"if what you eat causes pain, you ate something bad for you."
- if this was the case I couldnt eat much for 20 years. What you do not digest properly, causes pain. Even good, healthy food I couldnt digest, for years. That was painful.
Or food you react too, if you lack something, like enzymes, that need a optimal temperature to do their work.
There are chain reactions, co-operations in the body; not as easy as presented in this post. This or that diet may work for some, for others not. For people with an extended candida infection, nothing seem to work. They try to starve the candida, but it comes back.. etc.
Food that are bad for you, like junk food, may actually give you a high, first. Then a low energy for hours, days.
To differenciate between this is a learning process.