Some people are however always fat regardless of what they eat or don't. It's also not just about cico or activity level.

Sure. Even then, there's degrees and habits that curb/exacerbate the issue. The 64oz Big Gulp isn't doing anyone any favors, except the folks profiting off of sugar-water as a meal substitute.

Healthism is a neoliberal concept, there is only so much anyone can control their health by food choice.

Individualism is neoliberal, particularly in an economy that is constantly trying to nudge you into the most self-destructive decisions. But people still need health education. They need a material understanding of what their needs are and when a craving is productive or destructive. They need both medical professionals to guide them and sufficient autonomy to make informed decisions.

Also carbs as such are a staple of the human diet and always have been.

Carbs are a staple because they're cheap to manufacture, easy to store, and calorie dense. These yield economic benefits, but they can produce health problems as collateral. Case in point, you can track the rise in consumption of grains neatly with the rise in all sorts of dental problems in human populations.

We've also become significantly more sedentary over the last century. We have a host of tools for growing, transporting, and preserving foods year round that humans haven't always enjoyed. So a calorie rich diet that stores well isn't our primary concern anymore.