Is it the women's movement?

"According to our research, as much as two-thirds of the increase in adult obesity since 1980 can be explained by the rapid growth in the per capita number of fast-food restaurants and full-service restaurants, especially the former. It’s not hard to imagine how the explosive growth in these restaurants could fuel the obesity epidemic. Food served in these restaurants has extremely high caloric density, and almost certainly has contributed to obesity. We also found that the very modest growth in the per capita number of fast-food and full-service restaurants accounts in large part for the stability of adult weight in the period from 1960 to 1980, before the first major obesity upswing. During that period, the per capita number of full-service restaurants actually fell. Indications point to restaurant growth as the primary cause of increased obesity after 1980.

What caused this explosive restaurant growth? The principal driver seems to have been the increases in rates of labor force participation by women. As nonwork time for women became increasingly scarce and valuable over the last few decades, time devoted to at-home meal preparation decreased. Families began eating out more often. Indeed, the economists Patricia M. Anderson, Kristin F. Butcher, and Phillip B. Levine find that the rise in average hours worked by mothers can account for as much as one-third of the growth in obesity among children in certain families. In part, the rise in obesity seems to have been an unintended consequence of encouraging women to become more active in the workforce."

The Economics of Obesity, By Inas Rashad; Michael Grossman, Research Report, Summer 2004. [This link has deteriorated into one of those blob catch all things, but you can access it at "Access My Library" and register to become a user.

Just say no. And teach the kids, too.