Excellent point. People also made homemade meals made from scratch. My mom grew most of our vegatables. She also made just enough food to feed us.  Also, my parent's generation worked more physical jobs. For example my father worked a physical job in the trades. He would work an 8 hour day,  *then he would play catch  with my brother and I after dinner for about an hour. Think about it, Crossfit and many of these other exercise programs exist because many of the jobs in our economy no longer require any sort of physical prowess. Sadly, many of these jobs have been sent overseas or ceded to the Mexicans as "jobs white people won't do." These differences are something that this study ignores:  First, people are exposed to more chemicals that might be weight-gain inducing. Pesticides, flame retardants, and the substances in food packaging might all be altering our hormonal processes and tweaking the way our bodies put on and maintain weight. Second, the use of prescription drugs has risen dramatically since the ‘70s and ‘80s. Prozac, the first blockbuster SSRI, came out in 1988. Antidepressants are now one of the most commonly prescribed drugs in the U.S., and many of them have been linked to weight gain. Finally, Kuk and the other study authors think that the microbiomes of Americans might have somehow changed between the 1980s and now. It’s well known that some types of gut bacteria make a person more prone to weight gain and obesity. Americans are eating more meat than they were a few decades ago, and many animal products are treated with hormones and antibiotics in order to promote growth. All that meat might be changing gut bacteria in ways that are subtle, at first, but add up over time. Kuk believes the proliferation of artificial sweeteners could also be playing a role.  It couldn't have to do with the fact that many of us sit in an "ergonomically correct" cubicle all day, are too lazy to cook and refuse to make the necessary changes to account for these changes and correct the problem.