I think we all know that obesity is caused by the high carbohydrate and sugar intake of today, and too little exercise. Real fats (as opposed to transfats) have little to do with it. In fact we need some natural fat such as meat fat, oily fish butter, olive oil, avocado for our health.
Remember soft drinks when we were young? Very occasionally our Mums would buy a bottle of lemonade or dandelion & burdock and all the kids would get a glass. That would be it. These days many kids get a bottle each a day.
Fast food was fish n chips on a Friday. And two of us would share one lot of chips. These days it's MacDonalds food with its white rolls containing sugar, meat cooked in transfats, or KFC with its heavy coating of carbs cooked in unhealthy oils, or all the other coated, salty, junk food. Too many kids eat too much of it. Then there's breakfast. For us it was a boiled egg, or cornflakes in a bowl half the size of today's bowls. These days cereals, marketed as healthy, are in fact sugar-laden junk. Unless their mums know a bit about nutrition, and are tough enough to say NO when necessary, the kids don't stand a chance.
Then there's exercise. We could play out and run around all day. Some kids still can. But many have computer games and spend an unhealthy amount of time on them.
I'm 68 now and disgustingly healthy. I don't eat anything with grain in it (bread, cakes etc) but eat as much meat, fish, cheese, eggs and veggies as I like, plus a little fruit. Before I adjusted my way of eating I was piling the weight on, after retirement. I halted it at size 16. I'd have been at least a size 20 now, the way I was going, if I hadn't cut out the carbs.
Strange thing is, before I did this, I was always hungry. Now I rarely am.