The objections to this oversimplified reasoning usually point to the fact that, among other things, there's a documented rise in obesity among animals as well, across a variety of situations (feral rats, lab primates, domestic pets). Lab primates aren't eating out more or getting less PE in schools, which suggests the possibility of an environmental factor[1].
> particularly deep fried foods.
This is a very early-1990s understanding of nutrition. The low-fat recommendations pushed by the USDA and followed to a large degree by American consumers didn't do anything to halt the obesity rise, because excess dietary fat isn't nearly as bad for you as excess processed carbs/sugar.
Nope, we are fat because there are many cheap sources of calories, particularly deep fried foods.