Great response. Shame on the NYTimes for not accepting it!
In an op-ed titled Debunking the Hunter-Gatherer Workout in the Sunday New York Times on August 26, 2012, Herman Pontzer from Hunter College comments on a study that he published this July in PLos One.
As someone who has devoted his career to researching and promoting physical activity and preventing obesity, I object to Dr. Pontzer's conclusion that physical activity has nothing to do with obesity. This is a claim that surfaces regularly, so it needs to be addressed repeatedly and thoughtfully. A key point of rebuttal is that, based on their evaluation of the literature, the Institute of Medicine, Centers for Disease Control and Prevention, US Surgeon General, International Obesity Task Force, and the World Health Organization, among other groups, recommend physical activity as part of obesity prevention. However, let's take a look at the Pontzer op-ed and study.
The study was an interesting one. They studied the Hadza people of Tanzania who live a traditional hunter-gatherer lifestyle with little or no intrusion of technology. The investigators used the high-tech method of doubly-labeled water to assess energy expenditure, and compared findings to a sample of "Westerners". I have 3 main objections to the study and op-ed.
First, the results don't add up. The Hadza from Tanzania were on average 65 pounds lighter than the Western sample, and they were much more active, with the Hadza men walking 15-20 miles a day. How could they conclude there is no connection between physical activity and obesity? Dr. Pontzer compared total energy expenditure, which was actually a little higher in the Western sample. But overweight people expend much more energy than thin people walking the same distance. As pointed out by my colleague Steve Blair, the authors should have compared energy expenditure per kg of body weight, which would have produced a more accurate and obvious conclusion that the Hadza were much more active.
Second, they concluded diet alone is responsible for obesity, but their study had no measure of diet. Where is the basis for that conclusion?
Third, they made a sweeping conclusion that "inactivity is not the source of the obesity epidemic." They dismissed previous research that shows active people gain less weight. When they say "we are not going to Jazzercise our way out of the obesity epidemic" many people will hear "I don't have to exercise anymore." Did the authors consider the effects of their confusing message to the public, most of whose health is at risk from inactivity?
Because of the prominent placement of this op-ed in the Sunday New York Times, it is likely thousands of people are questioning whether they should bother being active as part of their quest to control their weight. If some of those people stop exercising because of this op-ed, that would clearly be a negative health outcome because inactive lifestyles are the fourth leading cause of death in the US and world. Did the authors consider the effects of their confusing message to the public, and are they prepared to take responsibility for discouraging people be active?