A new study bolsters evidence that obesity is increasing in kids in the US

I don't think we can narrow the dates down quite as much as you suggest, as there may have been a delayed reaction to whatever changed. I can think of several possibilities: increased use of plastics in essentially everything, increased use of seed oils because saturated fat was demonized, and increased carbohydrate consumption because all fats were demonized. Increased consumption of ultraprocessed foods might be a factor too.

It probably started a bit earlier than that, we may need to concerned ourselves with a process that took a decade or more to get going.

There has been far too much focus on CICO and exercise and all sorts of other stuff even though a lot of the rare stats for intake and exercise should suggest the population is just as healthy. Something went badly wrong and we need to identify it, its a epidemic that has been burning away for decades slowly but surely spreading.

Sometimes I read threads like this and feel like I'm taking crazy pills when people go "Oh we don't know why this is happening, is it plastics? Is it sugar? Seed oils?"

It's incredibly easy to eat a lot of calories and not be active. That's it. Portions are big, foods are calorically dense, and people work desk jobs instead of labor jobs. Kids can play video games or watch TV instead of playing outside.

As an analogy, to me it feels like looking at someone bleeding out from a gunshot and worrying if the lead in the bullet might be causing the person health issues.