Study leader Herman Pontzer of Hunter College in New York along with David Raichlen of the University of Arizona and Brian M. Wood of Stanford University measured daily energy expenditure -- calories per day -- among the Hadza, a population of traditional hunter-gatherers living in the open Savannah of northern Tanzania.
Despite spending their days trekking long distances to forage for wild plants and game, the Hadza burned no more calories each day than adults in the United States and Europe.
The team ran several analyses accounting for the effects of body weight, body fat percentage, age and gender. In all analyses, daily energy expenditure among the Hadza hunter-gatherers was indistinguishable from that of Westerners.
The study was the first to measure energy expenditure in hunter-gatherers directly; previous studies had relied entirely on estimates, Pontzer said.
Although the findings upend the long-held assumption that our hunter-gatherer ancestors expended more energy than modern populations, the findings suggest habitual metabolic rates are relatively constant among human populations and the current rise in obesity is due to increased food consumption, not decreased energy expenditure.
The findings were published in the journal PLoS ONE.