Lower energy expenditure can’t get all the blame for today’s rising obesity levels, if study of hunter-gatherer population is correct.
Results from a new study* published in the July 25, 2012 issue of PLoS ONE reveal that there is no difference between the energy expenditure of modern hunter-gatherers and Westerners, challenging the widely accepted theory that today’s sedentary lifestyle in Western countries is the reason for rising obesity levels. The findings are also significant for understanding our relationship to our ancient hunter-gatherer past, as the study subjects are members of a modern-day hunter-gatherer population that is believed to closely reflect the way our ancient hunter-gatherer ancestors once lived.
Led by Herman Pontzer of Hunter College in New York City, along with David Raichlen of the University of Arizona and Brian M. Wood of Stanford University, the research team measured the daily energy expenditure (calories) of members of the Hadza, a population of hunter-gatherers who live in the open savannah of northern Tanzania. The Hadza, because of their life-style, are thought by scientists to closely approximate the way ancient hunter-gatherers in Africa may have lived tens of thousands of years ago in what many consider to be a possible ancestral homeland for modern humans. They found that, despite a way of life that involved trekking long distances to forage for wild plants and game, the Hadza actually did not burn more calories each day than modern-day adults in the U.S. and Europe. In their analysis, they tested for effects of body weight, body fat percentage, age, and gender. The study was significant in that it was the first to directly measure energy expenditure in hunter-gatherers; before, scientists had relied primarily upon estimates.
It is surprising because modern sedentary lifestyles characteristic of those living in Western countries are thought to be quite different from those of hunter-gatherers, and by extension our ancient hunter-gatherer ancestors. This fact is raised by many as the cause of the current rise in global obesity. Moreover, it challenges long-held assumptions that our ancient hunter-gatherer ancestors, always “on the go”, must have expended more energy than modern populations. It also suggests that metaboloc rates are actually comparatively constant among diverse human populations.
“These results highlight the complexity of energy expenditure,” says Pontzer . “It’s not simply a function of physical activity. Our metabolic rates may be more a reflection of our shared evolutionary past than our diverse modern lifestyles.”
* Pontzer H, Raichlen DA, Wood BM, Mabulla AZP, Racette SB, et al. (2012) Hunter-Gatherer Energetics and Human Obesity. PLoS ONE 7(7): e40503. doi:10.1371/journal.pone.0040503