Taking the traditional wisdom head-on, scientists now report that eating too much — not exercising too little — may be at the core of long-term weight gain in children.
Conventional wisdom suggests that an increasingly sedentary and germ-free lifestyle, resulting in low daily energy expenditure, is a primary factor underlying rising rates of obesity in the US and elsewhere.
"Our study challenge that notion. We demonstrate that Amazonian children with physically active lifestyles and chronic immunological challenges don't actually burn more calories than much more sedentary children living here in the U.S," said Samuel Urlacher, assistant professor of anthropology at Baylor University in Texas.
This similarity in energy expenditure suggests that the human body can flexibly balance energy budgets in different contexts.
To investigate how children spend calories, Urlacher and his colleagues collected data from 44 forager-horticulturalist Shuar children (ages 5 to 12) and compared them to those of industrialized children in the US and the UK.
To measure energy expenditure, the researchers used gold-standard isotope-tracking and respirometry methods. This information was coupled with data reflecting physical activity, immune activity, nutritional status and growth.
The study found that Shuar children are approximately 25 per cent more physically active than industrialized children.
Shuar children have approximately 20 per cent greater resting energy expenditure than industrialized children, to a large degree reflecting elevated immune system activity.
Despite wide differences in lifestyle and energy allocation, the total number of calories that Shuar children spend every day is indistinguishable from that of industrialized children.
"These findings advance previous work among adults, showing that energy expenditure is also constrained during childhood," said study co-author Herman Pontzer from Duke University.
A key takeaway of the study is that rapid change in diet and increasing energy intake, not decreasing physical activity or infectious disease burden, may most directly underlie the chronic weight gain driving the global rise of obesity.
However, "exercise remains critically important for health and for weight management given its effects on appetite, muscle mass, cardiopulmonary function and many other factors," Urlacher said.
"Our results don't suggest otherwise. Everyone should meet recommended daily physical activity levels".
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