In this photo, from 1976, almost everyone is what we would now call slim. So what has happened? A sudden loss of willpower, as some rightwing journos claim? No. An obesogenic environment created by junk food manufacturers and their advertisers. 
The food companies employ scientists to make their products ever less resistable. The advertising companies employ psychologists and neuroscientists to break down our defences. They overwhelm our willpower.
Yet the billionaire press blames people for forces much bigger than ourselves, whether it is structural unemployment, indebtedness caused by housing costs or the obesity crisis. The individuation of blame sits at the heart of neoliberalism.
Its catchphrase is "personal responsibility". Yet no responsibility is attributed to the corporations, politicians and lobbysists responsible for such crises.
For the billionaire press to be right about this, it would have to identify a factor that caused the brains of much of the population radically to change in the course of 40 years. As no such factor has been proposed, the obesogenic environment is a more likely explanation.
And here, via @harryrutter, is a scientific paper that makes the same point, with evidence thelancet.com/journals/lanpu…
You'll note from the graph that 1976, by chance, was more or less the inflection point.
