This week the online journal PLoS One published a study that links the rising weight trend of the last few decades to a decline in physical exertion at work. Based on data from the Bureau of Labor Statistics, Louisiana State University exercise researcher Timothy Church and his colleagues report that "in the early1960's almost half of the jobs in private industry in the U.S. required at least moderate intensity physical activity," compared to less than 20 percent today. This trend, they estimate, translates into an average decline in energy expenditure of more than 100 calories a day. That difference, they say, corresponds very closely to the increase in weight measured by the National Health and Nutrition Examination Survey during the same period:
From 1960–62 to 2003–06 we estimated that the occupation-related daily energy expenditure decreased by 142 calories in men. Given a baseline weight of 76.9 kg in 1960–02, we estimated that a 142 calories reduction would result in an increase in mean weight to 89.7 kg, which closely matched the mean NHANES weight of 91.8 kg in 2003–06. The results were similar for women.
In other words, less arduous work seems to account for almost all of the increase in weight. Since people who focus on increased calorie intake claim that it too is an adequate explanation for the "obesity epidemic," our expanding waistlines seem to be an overdetermined phenomenon. While The New York Times calls Church et al.'s findings "one piece of the obesity puzzle," on the face of it that's one piece too many.
Just as we are daily warned about the perils of seductively cheap and dangerously delicious food, the Times story portrays labor-saving technology, the movement from backbreaking farm work to cushy jobs in air-conditioned offices, and even the convenient placement of computer printers as public health menaces. As I noted in my 2004 Reason cover story about the War on Fat, we tend to lose sight of the fact that both of these developments—the fact that making a living is much less physically demanding than it used to be and the fact that food has become much cheaper and easier to get, to the point where the fattest Americans are the poorest Americans—are overwhelmingly positive from a historical perspective. If the downside is that we need to consciously constrain our food intake and actively seek opportunities for exertion, that's a small price to pay for the enormous improvement in living standards that has made it possible for us to worry about weighing too much.