there are so many factors that go into your guts. whats required in order to break down certain vitamins from plants vs. animals, modern processing, genetic mutations, early diets... i've even read studies about gut health and birth. whether or not you are born vaginally or cesarean, because you collect bacteria from the mother during vaginal birth. though its not a for sure thing, it just can raise the chances of certain health issues in cesareans.
etc etc
anyways, yeah, its just complicated like that because our bodies are complicated and different. i'm no expert on dietary health but my conclusion from everything i've read or listened to from both sides and the neutral, is that there is no one diet answer for everyone.