“Life Is a Game of Turning Energy into Kids”

One of the simplistic models of obesity relies on the notion of a balance between calories a person consumes in foods and drinks and those burned in physical activity. Some people even go so far as suggesting food labels should tell us how much we’ll have to exercise to burn off the calories in that cookie. But evolutionary anthropologist Herman Pontzer is here to tell us this is simply wrong. Our bodies are evolved to handle the energy we consume and use to sustain life in a much more complex way.

What distinguishes humans from other species is big brains and big babies, says Pontzer. So our bodies evolved around the principle that life is all about turning energy into kids. This is the view through a lens of evolutionary biology.

Energy for Much More Than Physical Activity

In a recent interview, Pontzer explains how our bodies have evolved to consume and use a lot of energy:

“There has been a big change in human evolution, in the way that our bodies burn calories. We have ramped up our metabolic rates. Our cells are busier. We burn more calories every day than our ape relatives do. That’s because of all these really expensive traits that we have, these big expensive brains.

“Humans have big babies quite often compared to other apes. All those things take a lot of energy. So we’ve actually increased our energy expenditure as a species compared to other apes.”

We have trillions of cells, all using energy all the time for many different purposes that sustain life.

A Stable Burn Rate

So it turns out that physical activity doesn’t directly determine how much energy our bodies burn. Going for a run will not necessarily burn off all the extra calories in those Girl Scout cookies. This is because our bodies adapt to different levels of physical activity and maintain a relatively steady metabolic rate. The energy goes for other purposes when it’s not necessary for physical activity.

Pontzer saw this when he studied the energy expenditure of the Hadza people in northern Tanzania. These are people with a very active lifestyle of hunting and gathering food. But when he rigorously measured their energy expenditures, he found that “Hadza men and women burn exactly the same amount of energy that we burn in the U.S.” Our more sedentary lifestyles made no difference in this comparison.

Bodies Adapt

Pontzer found that body composition is a more reliable predictor of energy expenditure than physical activity. This is a finding that has been relatively consistent in other research. Burning more calories in exercise might improve the health of our bodies. But it does not lead us to lose weight. Our bodies adapt because they are adept in using energy efficiently to sustain our lives.

Click here for the interview with Pontzer and here for his research. For more on the role of exercise in energy balance and body composition, click here.

Diego at the Charles Darwin Research Station, photograph by Kaldari / Wikimedia Commons

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June 11, 2021