I'm not sure school lunches could reasonably be the culprit because we're talking a third and there's simply too much variation across thousands of school districts. Whatever it is has to affect everyone across the US mostly the same.

> There’s no way sugar is the root cause, since this wasn’t a problem back when it was the default sweetener.

You may want to check the quantities.

Also, back in the day, not every product contained sugar or glucose syrup.

It's probably a combination.

30-40 years ago, sugar wasn't in everything, or at least not in the levels it is found today. People also chuck down liquid sugar like there's no tomorrow, which is also something "new" that wasn't around 30-40 years ago.

People today are less active, eat much more calories, many in the form of sugar, and many in the form of fat.

The main problem is, even if you wanted to go back to a "1970s diet", you probably couldn't today. Processed food is everywhere.

HFCS is a sugar. The difference between HFCS and standard cane sugar is relatively minor - a 5% difference in the ratio of fructose to glucose.

There's some evidence HFCS is worse than sucrose (standard refined cane sugar) and some metabolic mechanisms to make that plausible, but it's a relatively minor difference compared to just the overall amount of consumption.

10 grams of "sugar" (sucrose) is 5 grams of fructose. 10 grams of high fructose corn syrup is 5.5 grams of fructose.

A diet going from 10 grams of any sugar per day to 50 or 100 grams of any sugar per day is going to have a drastically larger impact on health than if the 10 grams were sucrose vs HFCS.

Admitted, i'm an old fart, but when i was a kid, cake was something we had on sundays, sodas was something we got at a birthday party, and we had one, maybe two, and meals were rich in protein and fat, with carbohydrates usually being at the bottom. We spent the entire day outside, riding our bikes, playing (as in physical, not computer), riding skateboards, etc.

These days it almost feels like sugar has replaced a lot of the protein and at least some of the fat, and we eat a lot more of it.

Sodas are no longer a "monthly" event, but a daily event, and people will happily drink 2-3-4 sodas per day (or more). In our food, a lot of the protein has been replaced by sugar and fat as well.

And instead of running around, playing on the streets, kids these days sit in front of a computer/tablet/phone/tv/whatever.

Thank food corporations for pouring high-fructose corn syrup into everything.

GLP1 drugs were developed to manage blood sugar levels in diabetics. Weight loss was a side effect.

One of the issues that came up when they started getting popular for weight loss was shortages causing issues for diabetics that had been relying on them.