I think it’s oversimplifying it. It’s not black and white. “Overweight people are sick and miserable. Skinny people are healthy and happy.” It’s not that simple. I think everything is good in moderation. Who told you that diet is a main thing?

I am not sure how cognitive functions and mental health are directly related to diet. There is some connection of course but not direct. My cognitive functions don’t change when I gain or lose weight and I don’t become stupider or smarter all of a sudden. Also it’s kind of silly to assume that overweight people must be all miserable suffering with mental health issues. No evidence of that. Sure being very overweight will potentially cause health problems. But so is extremely underweight

In general our society is so preoccupied with weight and looks that I think that becomes a problem. Like being obsessed with staying skinny might be more dangerous for mental health that being overweight