I was thinking the same, moving to UK. Some people here are huge, by my native country standards, while in my country rarely was a fat person in my generation. But I remember as children going out once per month, for a restaurant meal, which by the way was quite healthy by today standards. No fast food, maybe 2 pizza per year, an icecream here and there. Rarely going to the cafe to have a cake, again, on my birthday, maybe. If I was behaving. We were out playing footbal and games morning til dusk. If I was more than one hour on PC, mom was coming to switch it off. Different habits.

And yes, fat people back then are considered average now.