Obesity is really more common now than it was back then.
Even when I was a kid, it seemed there weren't too many fat people. And when you saw one, they really stood out. When I was in elementary school, which was in the mid 70s-early 80s, there was only 1 fat kid in the class, and again, he stood out. And he wasn't even really fat, just "chubby."
Today, fat kids seem to be common, and nobody seems fazed by it.
I'm thinking because there's more fast food restaurants out there than ever, and people just don't cook at home... or when they do, they use processed food like instant potatoes or whatever. Not only is this contributing to obesity but also higher rates of diseases like cancer and high blood pressure. At a previous job I had, quite a number of people would bring those instant microwavable lunches to work and eat that for lunch. I'm sure those are really high in sodium and preservatives. I couldn't imagine doing that all the time.