""not the staple foods our various societies has thrived on for centuries!""
The white rice, pasta and wheat used in most breads (Spelt flour etc not included), isn't what we've eaten for centuries, or the same as what was traditionally eaten in the countries that the originated from. We have hybridised versions of the "traditional" grains once grown, as well as the traditional grains being rarely used and expensive (then there is the processing of the grains.
It is the white carbs that add little to our diets, but as said, they are filling and cheap.
Carbs also come from Veg sources, Swede, Sweet Potatoes, Squash, Beans, Peas etc and Corn (which my ancestors Native Americans made their bread etc from).
One of the issues is the constant availability of food, we not the staple foods our various societies has thrived on for centuries!don't go through "lean times", which naturally controlled our weight.
I comfort myself with the thought that my body, that stores fat ridiculously well, would have ensured my survival had I of lived in past times.
The reaserch from the Concentration camps (and other human experiments) shows that there are differences in the way our bodies use food and cling on to weight.