July 26, 2012 by APRIL McCARTHY
The Verdict Is In: Energy Expenditure Is Not The Problem, It's Our Food
Modern lifestyles are generally quite different from those of our hunter-gatherer ancestors, a fact that some claim as the cause of the current rise in global obesity, but new results published in the open access journal PLoS ONE find that there is no difference between the energy expenditure of modern hunter-gatherers and Westerners, casting doubt on this theory.
Speaking at the annual Castan Centre for Human Rights Law Conference in Melbourne, Dr Samantha Thomas said the war on obesity has failed because society has not placed enough emphasis on the food industry and corporate abuse.
"Obesity rates are still increasing because we put all the responsibility on the individual, but are completely reluctant to tackle the corporations that are part of the cause - the junk food companies, the soft drink companies, even the town planners who design new suburbs with no backyards or playgrounds," News.com.au quoted Dr Thomas as saying.
The research team behind the study in PLoS ONE, 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 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 U.S. 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.
A number of previous studies such as the research from Loyola University Health System also failed to support the common belief that the number of calories burned in physical activity is a key factor in rising rates of obesity.
These findings upend the long-held assumption that our hunter-gatherer ancestors expended more energy than modern populations, and challenge the view that obesity in Western populations results from decreased energy expenditure. Instead, the similarity in daily energy expenditure across a broad range of lifestyles suggests that habitual metabolic rates are relatively constant among human populations. This in turn supports the view that the current rise in obesity is due to increased food consumption, not decreased energy expenditure.
The authors emphasize that physical exercise is nonetheless important for maintaining good health. In fact, the Hadza spend a greater percentage of their daily energy budget on physical activity than Westerners do, which may contribute to the health and vitality evident among older Hadza. Still, the similarity in daily energy expenditure between Hadza hunter-gatherers and Westerners suggests that we have more to learn about human physiology and health, particularly in non-Western settings.
"These results highlight the complexity of energy expenditure. It's not simply a function of physical activity," says Pontzer. "Our metabolic rates may be more a reflection of our shared evolutionary past than our diverse modern lifestyles."
Dr Thomas, a senior research fellow at the Monash University School of Marketing, said more should be done to prevent obesity, rather than simply telling people to lose weight.
"It is easy to say ''I do the right thing, why don''t they?'', but for some people, for a variety of reasons, it is very hard to make the right decisions. We really need to create a healthy environment to help people do that," she said.
Dr Thomas said the anti-obesity fight should be similar to the war on smoking, with big tobacco companies held accountable rather than individuals labeled weak or lazy.
"With the anti-smoking movement, we realized that tobacco was being heavily marketed at adolescents and we were disgusted. Junk food is heavily marketed at children and adolescents but, instead of trying to stop that, we just put all the responsibility on parents," she said.
Although parents have a huge influence on a child's dietary habits, there must be some measure of guidance coming from reputable organizations and corporations who can help lead the charge. Personal resposibility is key only when people have been informed of the facts. We are not being informed of the facts from the food industry and it's time for that to change.
April McCarthy is a community journalist playing an active role reporting and analyzing world events to advance our health and eco-friendly initiatives.