The incidence rate of genetic issues generally doesn't change much over time due to how slow genes changes, so an increase in obesity rates from 5% to over 40% in just a few generations suggest the cause is very unlikely to be due to genetics.

Not exclusively genetic but inclusively genetic. There are of course other factors involved and I think genes are a big one.

In the US, I'm convinced that it was the food pyramid.

As a kid in the 80s, I wondered how it made sense that my diabetic father was told to follow the same model as non-diabetics, which emphasized carbohydrates.