Roberta Jupp gives my theory a very different twist by pointing out that just as medical advances make obesity cheaper, so does health insurance. The more heavily you're insured against heart disease, the more likely you are to have that second scoop of ice cream. I love this observation, but I'm not sure that insurance contracts have changed enough in the past 10 years for us to pin all the blame on them.
Besides medical advances, my other theory was that low-calorie foods encourage people to eat more, so their weights might go either up or down, depending on how much more they eat. (Actually, my column referred to "low-fat" foods; several readers correctly pointed out that I should have said "low-calorie," because low-fat and low-calorie are not the same thing.) Raphael Laufer points out an interesting test of this theory: It suggests that we could see movement toward both extremes, as some people use low-calorie foods to indulge themselves and others use them to lose weight. I haven't managed to find numbers that would let me perform this test.
Steven Zara points to Home Shopping Networks, TiVo, cell phones, and cable/satellite TV as new technologies that tend to keep the potato on the couch. Heidi Hirst raises the key follow-up question: How does the obesity explosion correlate with changes in TV viewing hours? And Rusty Bastian asks a great related question: Did obesity increase at a different rate among those who have physically demanding jobs? Sadly, I don't know the answers.
Cindy Shank, Greg Diamond, Paul W. Horn and others point to the advent of Prozac and similar antidepressants. Obesity might be a side effect of such drugs or, more interestingly, maybe Prozac makes you worry less about being obese. But the prize for the most alarming theory goes to Paul Townsend, who writes, "Aliens are force-feeding and fattening us up like geese for liver pate."
There are still several thousand e-mails I haven't gotten to, and I'm sure I'll never get to all of them. If you had a great idea I overlooked, I apologize.