The bit you quote that sticks out is that the obesity “epidemic” has levelled off, as though the US population has adjusted to an environmental change. I bet this levelling off has not happened here in France yet.

Assuming it has leveled off, we now have a scenario like this:

Something started affecting the USA in the late 70s, hit Britain and Australia in the late 80s and the rest of the western world a few years later. Whatever it is has had its complete effect on the US population, which has now stabilized at a new equilibrium.

There are candidates that might have that sort of worldwide rollout: modern food oils, cheap fast food (but what is it in that fast food?), change in home cooking styles and so on. I won’t list HFCS since that isn’t used much in Europe and we’re getting fat too. Lattes? Hip-hop? Gosh, you could come up with a huge list of things.

My hunch is Borlaug’s dwarf wheat, which followed that rough pattern of being grown throughout the world starting in Mexico and the USA. It’s all dwarf wheat in Aus and the UK and France. Dwarf wheat’s yields just conquer in a commodity market. Nearly all wheat in the world is Borlaug’s dwarf wheat. It saved India from starvation.

Dwarf wheat gives you cheap packaged wheat-based food since wheat yields are so good the price has dropped. If the modern dwarf wheat does have a dietary problem for a percentage of folks then when you combine convenient, easily storable wheat foods with dwarf wheat dietary issues you might get something near the obesity curve over time.

Now, of course, we have obesity as a major health problem in India instead of starving kids. That is still an improvement.