Is meat a meme or not? I hear a lot of arguing over the best diet. Vegan is the best, meat is the best, mediterranean is the best, etc.

I used to follow a mediterranean diet but I've also had mental issues for years. Recently I've noticed, the more I cut from my diet, the better I feel. Quitting gluten basically cured my depression and anger issues. I don't even have celiac. Nuts, beans, seeds, and non-gluten whole grains increase my OCD and give me racing thoughts. So I cut those out and feel significantly better. Every day I eat chicken, eggs, white rice, kale, and a few other things.

I wonder what would happen if I cut out kale for example? What if I cut out white rice, because I've heard grains in general cause problems. But I'm underweight and I need calories, so I would have to increase my meat intake. Is this a bad thing? I've heard many stories of people eating more meat really helped them out with whatever issues they had. But then how come the longest living civilizations don't eat a lot of meat?

Help.