The other thing that came after the rise of vaccines was women not staying home with kids, and hence kids not running around playing for hours after school but sitting like lumps in daycares or in front of the TV, and then the computer, eating chips and junk. No moms cooking healthy dinners and the appearance of the microwave also meant more easy snacking and more fast and convenience food. It's not a tricky biological mechanism, it's a change in society and daily habits. And a picture is what made me lose weight thirteen years ago; I was nowhere near barge-size, but one night my husband and I went out to dinner and my MIL took a photo of us. I was so horrified when I saw that photo that I decided that was it, started counting calories, and lost 40 pounds (and have not gained it back).