The real question is why people eat more now than they did in 1961. I think convenience and cost is a big part of it. Food is much more affordable than it used to be, so people can afford to eat a lot more soda and potato chips. Today, you buy 12-packs of soda, instead of 6-packs. Potato chips and every kind of junk food comes in bigger packages, tastes delicious, and is cheaper. More people own two cars, making it easier to shop by car as often as desired rather than by bus or less frequently. For example, my grandparents had one car, so when my Mom was growing up in the 60s, she said her grandma would take the car once every TWO WEEKS to shop on the weekend. Today, my husband and I shop a few times a week and it's super easy and convenient.