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 U.S. and elsewhere.
But in a recent study from Baylor University, researchers found that eating too much—not exercising too little—may be at the core of excessive weight gain.
They found forager-horticulturalist children in the Amazon rainforest do not spend more calories in their everyday lives than children in the United States, but they do spend calories differently.
That finding provides clues for understanding and reversing global trends in obesity and poor metabolic health.
The study is published in Science Advances. One author is Samuel Urlacher, Ph.D., and assistant professor of anthropology at Baylor University.
In the study, the team showed that Amazonian children with physically active lifestyles don’t actually burn more calories than much more sedentary children living here in the U.S.
They collected energetics data from 44 forager-horticulturalist Shuar children (ages 5 to 12) and compared them to those of industrialized children in the U.S. and the United Kingdom.
The Shuar are a population of around 50,000 individuals living in the isolated Amazon region of Ecuador.
Without easy access to stores and labor-saving technology, they continue to rely predominantly on a subsistence-based lifestyle of hunting, fishing, foraging, and small-scale horticulture.
The team found that Shuar children are approximately 25% more physically active than industrialized children.
They have approximately 20% 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.
This similarity in energy expenditure suggests that the human body can flexibly balance energy budgets in different contexts.
Standard models in human nutrition assume that habitual energy use is “additive,” such that exercise and other metabolic tasks increase total daily energy expenditure, which is the total number of calories that humans burn each day.
Consistently exercise more, spend more total calories.
However, that model has been increasingly challenged by studies suggesting that total daily energy expenditure is “constrained” within a relatively narrow human range.
The team says because tradeoffs underlying energy constraint may often limit physical growth, such constraint has implications for understanding childhood growth faltering and its associated increased risk for adult obesity and metabolic diseases such as type 2 diabetes and hypertension.
They say the rapid change in diet and the 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.
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