Our sedentary lifestyles don't explain the obesity crisis.


Finbarr O'Reilly/Reuters

PROBLEM: The equation is simple enough: Consume more calories than you burn off through physical activity, and you will gain weight. As such, the largely sedentary nature of the Western lifestyle is often blamed for our culture's rising levels of obesity. How legitimate is this claim, and do we desk-workers expend significantly less energy each day than do those who lead more "traditional" lifestyles?

METHODOLOGY: The Hazda, a hunter-gatherer population in Northern Tanzania, were used as a modern manifestation of the foraging lifestyle: they procure their food without the help of modern instruments and do not consume processed foods. Using wearable GPS devices, portable respirometry systems, and urine tests, researchers tracked the Hazda's daily walking distances and measured their energy expenditure when walking and resting. This data was compared both to individuals and to populations, comprising Western, market, and farming economies.

RESULTS: As expected, the Hazda were, on average, much more active than members of Western society. But in a surprising twist, there was no significant cross-cultural difference in total energy expenditure between people of similar age and body composition, at least partly because we burn more calories just sitting around than do the Hazda.

CONCLUSION: Lifestyle was not shown to be a contributing factor to one's total daily energy expenditure. In fact, total energy expenditure is remarkably consistent across global cultures and economies, and is perhaps "more a product of our common genetic inheritance than our diverse lifestyles." So whether you are hunting down and killing your dinner yourself or grabbing take-out after sitting in front of a computer all day, the calorie intake needed to supplement your energy expenditure is more or less the same.

IMPLICATIONS: With differences in energy expenditure taken out of the above equation, these results seem to indicate that it's increased calorie consumption that is contributing to obesity (supersized soda, anyone?). However, the researchers are careful to point out that they are not attacking exercise:

"Physical activity has important, positive effects on health, and increased physical activity has been shown to play an important role in weight loss and weight-maintenance programs."

The full study," Hunter-Gatherer Energetics and Human Obesity," is published in the journal PLoS One.

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