Nutrition: Glucose spikes

My social media is flooded with nutrition tips. I'm not allowed to eat a lot of things, I should fast for at least sixteen hours - no, eight. Or not at all? My body doesn't know when it's day or night, some say, and I shouldn't eat anything for four days at least once a year, others say.

I probably have high cortisol levels. I think that because I know what is known as brain fog, sometimes I'm tired and then I eat fructose from berries. But I read that this is also dangerous. I have the feeling that everyone is going a little crazy, and yet I know that there must be something to some of it, because only a few things are really good for me when I eat them. I can't tolerate gluten, nor lactose or too much histamine. And I sometimes wonder how humanity has managed to hold out until today. Diarrhea in ancient times must have been murderous.