It has long been assumed that a lack of physical activity is one reason for the alarming rates of overweight and obesity seen in the United States and other developed countries. According to this theory, our bodies have evolved to be far more active than they are with today’s typical sedentary lifestyle, and therefore the body burns fewer calories than it would with a substantially higher level of physical activity.
While it seems reasonable, this explanation has not held up well to scientific scrutiny — including a new study involving people whose lifestyle could not be more different from what is typical in Western countries.A research essay was published in The New York Times, researchers decided to examine whether a consistently higher level of physical activity corresponds to a consistently higher number of calories burned by the body.
Their subjects were members of the Hadza tribe in Tanzania, a group that lives much the way all humans are believed to have lived before the agricultural revolution began some 12,000 years ago. The Hadza live in grass huts and spend the day gathering food, with the women digging up roots and picking berries while the men hunt with traditional poison-tipped arrows and gather honey.
As a separate article in the Times notes, men walk an average of seven and women an average of three miles each day. While this represents significantly more physical activity than the typical American gets, and the Hadza burn just as many calories through exercise as would be expected, their overall energy expenditure — the number of calories burned — is no greater than what is typically seen in more sedentary people. This stasis in energy expenditure supports the idea that the Western diet is more responsible for overweight and obesity than is a sedentary lifestyle.