Without going to a "name brand" diet (keto, vegan, or whatever), just pay attention to what you eat and what your brain feels like a few hours afterword. I found some foods (certain chocolates, unfortunately) where, somewhat less than an hour after I ate it, it felt like someone had kicked my brain.

When you notice something like that, stop eating it. You may be able to add it back in small quantities later, but for now, just stop.

When you've identified the major ones and stopped eating them, then take stock of where you are. Is it enough? Or do you want to go further?

We started being very careful what we eat because one of my daughters had extreme food sensitivities. I said "Nah, not me, I'm good". But I felt a lot better/less mentally foggy as well.