[jacques_chester]

I know what you're saying, but consider the counterfactual (ie, almost all history to this point).

In the absence of cheap, tasty food, obesity is rare.

When cheap, tasty food is abundant, so too are overweight and obesity.

On a population level it looks very much like cheap, tasty food is both necessary and sufficient. Without an increase in per-capita calories, there can't be an increase in population BMI.

The reason we call all these other phenomena strange is because we've never had tens of millions of overweight and obese subjects before. Sample sizes of tens of millions throw up new and interesting outliers. It's only going to get weirder.