A few weeks ago I had a very bad experience with a little bit of grapefruit. I became immediately depressed and feel strange uncomfortable sensations on the sides of my throat. This feeling lasted about a day of two. I looked up grapefruit and a mention about naringin made me very curious. Some of you have probably heard about quercetin, naringin(grapefruit), rutin, etc. Well it turns out many of these so called beneficial compounds disrupt Cytochrome P450 enzymes which are responsible for steroid hormone metabolism.
Examples
CYP3 - Testosterone metabolism
CYP7 - Bile acid synthesis
CYP51 - Cholesterol biosynthesis
I would guess some compounds are more potent than others. I have been eating kiwi occasionally and it doesn't have such a negative effect. I have become more wary of plant foods as a result. I probably have some level of tolerance that I cannot exceed. Perhaps, I may do better without any plant phenols/sterols.
I had suspicions about plant polyphenols when I became aware of compounds such as tannins and phytic acid. Even tannins and phytic acid are technically antioxidants and we know that these are not good. It seems the term is being thrown around recklessly as a cheap advertising scheme and the public is not aware of the entire story.
Phytosterols probably affect the P450 complex also.