Earlier quoted context omitted.
olive oil has been widely available for the last 7000 years, butter for ten thousand years, but the obesity pandemic is only 50 years old
But they were relatively expensive and scarce. And no-one is getting fat by drinking litres of olive oil or eating tubs of butter. It's a combination of more high-calorie convenience foods and a more sedentary lifestyle than even just 50 years ago.
the cost of edible oil has not been a bar to access to calorie-dense foods for at least centuries if not millennia
clearly the proximate cause of obesity is eating more and metabolizing less (both by way of lower exercise and lower basal metabolism). but why are people doing that? did they lose the gene for willpower in a single generation? that seems implausible
it seems to closely follow industrially-mass-produced foods, but the relevant feature of those foods is clearly not that they are more convenient or higher in calorie density than a can of crisco or an amphora of olive oil; they aren't