First time I ever switched to vegetarian was after my first psychedelic experience.
Almost all times afterwards I have switched, but eventually I go back to my regular diet, although it seems that over the years, perhaps due to the trips, the diet I have gets more and more selective.
Something else I noticed, perhaps tangentially related, but any times I have physically traveled to different parts of the world where one can experience cultural disillusionment, the tendency has been to switch over to a plant based diet.
I don't know if it's because I don't trust the food right off the bat and I'm doing it due to some safeguard mechanism, or if it's because part of my awareness is more awakened by the strange and foreign reality around me and then my more awakened awareness is somehow drawn to simpler / cleaner foods.
On the flip side of all of this, I have often done fasts or decided I need to be more careful about what I eat, and the result has often been an enrichment of the kind of subtle awareness of the intricacies and complexity of interconnections that the matrix of reality is build on... if that makes sense.
To myself at least I have proven that what you put in you (be it food or medicine or even ideas) has an effect on your perception and the abilities of your perception as well.
Cleaner diet = cleaner mind.