Vegan or vegatarian chess players
Like I said, different ways of eating work for different people with different neurobiologies.

I don't want to get into an argument with vegans, but here's a couple of videos that I think are worth watching. I respect Dr. Cywes and think he's intellectually honest.
Part 1 discusses vegan diets (with a keto perspective). Part 2 discusses vegetarian diets.
Dr Robert Cywes - Is Keto Possible on a Vegan Diet (Part 1)
https://www.youtube.com/watch?v=DAq64uQNeKk
Dr Robert Cywes - Is Keto Possible on a Vegan Diet (Part 2)

I have been vegan practically since i was born and I ate meat for a while,but I became vegan again, and have improved my chess

Your body does not need protein from meats, plant protein is perfectly sufficient. Most major health organizations agree that you can be perfectly healthy on a vegan diet, and most people (at least in the US) eat too much meat.