None. I had experimented with low carb/keto diets for years for no more than a few weeks at a time, I find the theory is quite interesting. Never had the willpower to power through it for longer but it left me that empirical sensation that I function a lot better when cutting carbs.
A month ago I started keto again, and I've started to notice that some keto-friendly foods still give me some kind of physical discomfort, like bloating and other digestive issues. I've never been diagnosed with anything, but I wanted to get rid of everything that may cause gut discomfort, since many scientists espouse the idea that mental health is directly correlated to gut health and the main purpose is to understand if I can function better.
So I got rid of:
* all FODMAPs (https://en.wikipedia.org/wiki/FODMAP), recommended against for all IBS sufferers
* all sweet stuff, especially fruit
* foods containing histamines (http://www.histamineintolerance.org.uk/about/the-food-diary/...)
This list is mostly experimental: on keto diet I feel myself shrinking down (i.e. the opposite of bloating), and it helped me to see the real effect of some kind of foods that I've always eaten but I've never been able to see the real effect they have on my body.
Anyway, this restriction doesn't leave very much, but I mostly live on unprocessed meat, eggs, butter, zucchini, bell peppers, olives (technically containing histamines but whatever), good quality cheese, some cream.
It's an interesting ride, not very scientific but I'm not trying to write a paper here, I'm just trying to eat what my body likes and avoid what my body doesn't handle well. And as an anecdote, yesterday, I ate onions again after 2 weeks of restriction, a vegetable I've probably eaten once a day for all my life, and I instantly felt like I was exploding from the inside. How haven't I noticed till now?
Some seem to joke that cutting out food groups is the reason for food intolerance: you are fine all your life, you get in the no gluten craziness and now you can actually feel sick when you reintroduce it in your diet. It's funny and it's also partly true: I could eat anything without any problem and now I feel measurably different on a lot of different nutrients.
Nutrition is rocket science.