Nitack, and many people in this thread, seem to be missing the point.
The question is "why are we getting fat" (as a nation—or a society). Neither of Nitack's "sides of the equation" address this.
I will give a specific example so as to focus the issue. You can read here:
Migration, Social Change, and Health ... - Google Book Search
about Samoan immigrants who move from western agricultural Samoa to more modernized areas in California and Hawaii. When living in western Samoa, they have typical body forms (they are not typically obese nor prone to having adiposity)
When modernizing, Samoans (on average) become obese with serious health consequences. There are studies relating energy expenditure before and after modernization as well as dietary differences. Different studies suggest different things. But, the point is, we are getting fat (speaking as a resident of the U.S.).
Both our diet and our daily activities have changed over the past couple hundred years and now over 70 percent of Americans are overweight. What exactly is the cause of this? What exactly is the cause of a Polynesia immigrant to a modern, urban community gaining an average of some 30 odd pounds?
Is there a scientifically supportable answer to this?
~modest
