What children of the Amazon can teach us about weight gain

But, Urlacher wondered, were their wiry frames a result mostly of their active lives? As a postgraduate student, he had worked with Herman Pontzer, an associate professor of evolutionary anthropology at Duke University, whose research focuses on how evolution may have shaped our metabolisms and vice versa (you can read more about his work here.)

In Pontzer’s pioneering research with the Hadza, a tribe of hunter-gatherers in Tanzania, he found that, although the tribespeople moved frequently during the day, hunting, digging, dragging, carrying and cooking, they burned about the same number of total calories daily as much-more-sedentary Westerners.

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Pontzer concluded that, during evolution, we humans must have developed an innate, unconscious ability to reallocate our body’s energy usage. If we burn lots of calories with, for instance, physical activity, we burn fewer with some other biological system, such as reproduction or immune responses. The result is that our average, daily energy expenditure remains within a narrow band of total calories, helpful for avoiding starvation among active hunter-gatherers, but disheartening for those of us in the modern world who find that more exercise does not equate to much, if any, weight loss. (Pontzer’s highly readable new book on this topic, Burn, will be published March 2.)

Pontzer’s work focuses primarily on Hadza adults, but Urlacher wondered if similar metabolic trade-offs might also exist in children, including among the traditional Shuar. So, for a 2019 study, he precisely measured energy expenditure in some of the young Shuar and compared the total number of calories they incinerated with existing data about the daily calories burned by relatively sedentary (and much heavier) children in the United States and Britain. And the totals matched. Although the young Shuar were far more active, they did not burn more calories overall.

But young Shuar differ from most Western children in so many ways, including genetics, that interpreting that study’s findings was challenging, Urlacher knew. But he also was aware of a more comparable group of children only a longish canoe ride away, among Shuar families that had moved to a nearby market town. Their children regularly attended school and ate purchased foods but remained Shuar.

So, for the newest study, published in January in The Journal of Nutrition, he and his colleagues gained permission from Shuar families, both rural and relatively urban, to precisely measure the body compositions and energy expenditure of 77 of their children between the ages of 4 and 12, while also tracking their activities with accelerometers and gathering data about what they ate.

The urban Shuar children proved to be considerably heavier than their rural counterparts. About a third were overweight by World Health Organisation criteria. None of the rural children were. The urban kids also generally were more sedentary. But all of the children — rural or urban, active or not — burned about the same number of calories daily.

What differed most were their diets. The children in the market town ate far more meat and dairy products than the rural children, along with new starches, such as white rice, and highly processed foods, such as candy. In general, they ate more and in a more modern way than the rural children, and it was this diet, Urlacher and his colleagues conclude, that contributed most to their higher weight.

These findings should not romanticize the forager or hunter-gatherer lifestyle, Urlacher cautions. Rural, traditional Shuar children face frequent parasitic and other infections, as well as stunted growth, in large part because their bodies seem to shunt available calories to other vital functions and away from growing, Urlacher believes.

But the results do indicate that how much children eat influences their body weight more than how much they move, he says, an insight that should start to guide any efforts to confront childhood obesity.

“Exercise is still very important for children, for all sorts of reasons,” Urlacher says. “But keeping physical activity up may not be enough to deal with childhood obesity.”

New York Times