The stigma around weight gain has been reliant on this argument of overeating for so long, while the research has indicated that there's a lot going on behind the scenes that has to be considered.
"obesity is innate, that weight regulation is not governed by a uniform tally of “calories in–calories out,” and to quote Jules Hirsch, that “there is a biochemical or basic biological element in what it is that we call `willpower.'”5 The views of many Americans notwithstanding, weight is clearly far from being entirely within an individual's control. Genetic predispositions, in tandem with the development of food environments that facilitate overeating and built environments requiring minimal energy expenditure, may help explain why so many Americans are obese today."