Consumption, Not Inactivity, to Blame for Obesity

Amanda Alvarez

Posted Aug 4, 2012

Challenging one of the most fundamental beliefs in our weight-obsessed culture, a group of researchers has found that physically active hunter-gatherers don't necessarily burn more calories than Westerners.

The new study, published Wednesday, claims that modern humans share the same energy needs as their Paleolithic ancestors but just consume more. The research into cultural differences in physical activity and diet suggests that rising levels of obesity are the result of more than just sedentary lifestyles.

It has been hard to pin down what exactly about modern life is responsible for obesity because data on the eating and activity habits of people before the industrial age are almost nonexistent.

But now, researchers led by anthropologist Herman Pontzer of Hunter College in New York visited Tanzania, where a group called the Hadza live in a traditional "hunter-gatherer" manner, foraging for tubers and berries and hunting on foot with bows. The Hadza, numbering about 1,500, don't have electricity, and their diet consists almost entirely of wild food such as honey, baobab fruit and meat.

The researchers expected that the Hadza expend a lot more energy than typical Americans, with their active lifestyle. They walk an average of 3.6 miles (women) and 7 miles (men) a day and were not only more physically active than Westerners but also have lower body fat.

But the Hadza didn't burn more energy than Western men and women.

"They are able to maintain a more active lifestyle and use the same number of calories," Pontzer said.

Instead of being more efficient -- their metabolic rates are what would be expected for their body size -- the Hadza used the same amount of energy to get different things done.

"A large proportion of their energy is spent on physical activity, and a smaller proportion is spent on other things," he said.

But in both Hadza and Western populations, there was no correlation between physical activity and body fat. Pontzer says the implication is that energy intake -- in other words, how much people eat -- is the main factor behind obesity's prevalence in Western populations, not lifestyle differences.

The research was published Wednesday in the journal PLoS ONE.

Likely one-of-a-kind look

Dale Schoeller, professor of nutritional sciences at the University of Wisconsin-Madison, said this study is, to his knowledge, the only analysis of energy budgets of an ancient lifestyle. He agreed with Pontzer's conclusion, that there is not a huge difference in energy use across very different populations.

"Most people assume that being sedentary causes obesity, but there is a growing base of data that obesity causes people to be sedentary," said Schoeller, who was not involved with the study.

The highly physical lifestyle of the Hadza contributes to their health -- they don't suffer from Western diseases such as diabetesor heart disease. But physical activity, Pontzer says, doesn't explain the difference in obesity.

"It happens to be that (physical activity level) does not correlate well with how fat you become," he said.

"We tend to say that obesity is a two-part problem: eating too much and not enough exercise," Pontzer said. "But emerging evidence is that population differences in obesity aren't related to energy expenditure but more to how much you eat. I'm not saying that physical activity isn't important, but it's not going to solve the global obesity problem."

©2012 the Milwaukee Journal Sentinel

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