I come from a country where the absolute majority of people were slim when I was growing up. It's changing now, but the average size is still far smaller than in UK. And all this is because one reason only: FAT SHAMING. Now I have to say in advance, I DON'T AGREE WITH ANYTHING I'm going to say below and I do think it's HORRIBLE. I'm just sharing the experience.
-Fat people (kids, grownups and old people) were and still are shamed everywhere and by everyone: other kids, teachers, employers, random people in the streets, shop assistants, relatives and parents - everyone. Not a day will go by without someone (and you're lucky if it's just one) person mentioning that you're fat, look awful and you need to stop stuffing your face and lose weight (and that's putting it politely).
-If you're a bigger person, you will have issues at work. Especially if your duties are representative/dealing with customers. If you're size 16, you won't be hired for these roles and no one will faff about with excuses, they will tell you your appearance is unsatisfactory.
-If you're a fat girl - no man would look at you. If you're a fat boy - you won't have a girlfriend.
-You will really struggle to find clothes if you're anything more than size 12. Above size 16? No chance. Tailoring or internet shopping abroad.
-Reasons for being fat such as 'mental issues'? You'd be laughed out of the room in unison and would be told to stop stuffing your face and start moving your arse. Any doctor would tell you the exact same thing. Psychiatrists/psychologists would keep quiet if not asked, but if you'd mentioned your weight - they would tell you the same (and this is from personal experience).
-'I'm a real woman', 'I'm rocking my curves' - people would die laughing. And when they catch their breaths, they would tell you that size 8 (or 10 at a push) is curvy. Size 16 is a cow. Above that? Monstrosities not worth talking about.
-There was a program on telly. I didn't see it, but as I understand, it was something to do with bigger girls being beautiful, plus size modelling, that sort of thing. It was taken off-air after a few episodes due to lack of attention. Judging by comments after the program, viewers were genuinely baffled: why would any TV channel choose to show these fatties and pretend they're attractive? Is this supposed to be a comedy? Not funny.
So basically it comes to this: if you're fat - you don't exist. No one cares about your tiredness or mental health issues. Don't gain weight/lose it or stay in the outskirts of society.
There are far more things, but these are enough, imo. Now again, I don't agree with any of it. The population IS slim, though. But the cost is also ridiculously high.
I came to UK 10 years ago. Back home, I was considered to be properly chubby/bordering on fat (5'11'' size 14 back then). Here in UK people called me slim. Being here, I've gained loads of weight (pregnancy and other issues) and was size 18/20. Here I was called 'plus size', but generally no one batted an eyelid. Back home I was a monstrosity, people didn't even laugh at me, they pitied me. Then I lost weight and I'm currently size 6/8. Now I get some grief and skinny shaming here in UK. Back home I'm considered to be absolutely normal. Slim, but not skinny at all. Medically I'm on the verge of being underweight, but I'm happy with my size.
Ah, but there are a few GOOD things to mention about 'back home', though. People still cook and teach their kids to cook from scratch and junk food (in shops and fast food joints) is far more expensive than healthy choices. What surprised me here in UK, is that you could get a meal from McD/KFC and the likes for practically nothing. Yet back there (ironically) these kinds of places are considered to be a luxury, as you can easily get a proper good meal in a decent establishment for far less. Also, fast food availability. For example, the city with a population of 295 000 has 1 McD, one KFC (which closed down as wasn't popular), one PizzaHut, one Subway and one Hessburger.