In the Simpsons episodes where Homer tried to gain weight for disability, his goal weight was 300 lbs. His normal weight was somewhere in the mid 200’s. The most famous American fatty on TV would barely stand out nowadays. Hell, in a lot of places, he could pass for relatively fit.I suspect the model there is meant to be a flattering presentation, but there is no doubt that what qualified as fat or chubby has changed markedly since that ad which is from the 50s, I think?. Even in the 70s most people, and certainly kids were much slimmer than now. People who weren't there can look at candid street photography of crowds for an illustration. Being very seriously overweight was really something mainly seen in the middle aged or older - people who had had time to eat themselves huge. With the normal kid's lifestyle - walking everywhere before everyone had a car, walking to school twice a day, playing outside actively not inside stuck at a console, active games in the playground at breaktimes instead of hunched around phones, and with food costs being actually a far larger part of the average wage than now and thus simply being more limited, it was simply harder to get children fat than it is now in a time of totally sedentary lifestyles and very cheap, calorie-dense food everywhere. Endless snacking between meals is cheap and possible in a way it never used to be unless you had money coming out of your ears. Sweets were a once a week thing for many in the 70s.
Compare and contrast now, when I see kids waiting for the bus at 8am with a can of Coke and a chocolate bar every single morning. Maybe instead of breakfast, but just as likely on top of breakfast. They have the money, you see them queuing in the local shop in the morning and after-school they buy sweets and fizzy drinks too. Affluence plays into this, for sure.
The 70s notion of a fat kid was maybe 10lb over the top weight they should be - enough to look a little chunky. A kid that size would stand out in class given everyone else was generally skinny. Now they have big sloppy beer bellies, or look like little spherical Sumos and it's out if the question to call them fat. I saw a kid maybe 9 years old following his mum at the supermarket the other day who was so all-over fat he waddled and had several chins. You really wonder if the parent even acknowledges it as a problem.
Even in the 80s it was vanishingly rare where I lived to see the kind of fat kid who seems to make up 20% of classes now- and whose parents would have a defensive, teary meltdown if you suggested - correctly- their kids was badly overweight and they should reassess the family diet.
Also I am imagining the fuss if a company named a line 'chubbettes' now.