And it may have influenced the way our jaws and teeth evolved

We might not think of chewing as a strenuous activity, but new research suggests it uses a surprising amount of energy. The way we mash up our food may have even played a role in how humans evolved. 

In a study published in Science Advances, researchers outfitted 21 participants with plastic astronaut-like helmets and measured their metabolic rates, or how much energy their bodies were using, as they chewed.

But the participants weren’t served any five-course meal—they chewed on flavorless, odorless gum. 

“This way it doesn’t activate the digestive system to the same extent as it otherwise would,” co-author Adam van Casteren, a biomechanics researcher at the University of Manchester in the United Kingdom, tells New Scientist’s Jason Arunn Murugesu. “We wanted to measure just chewing or as close to chewing as we could get.”

The volunteers first reclined under the bubble-like hood for 45 minutes to provide a baseline measurement. Then, they chewed on two types of gum—one softer and the other stiffer—for 15 minutes, while researchers measured carbon dioxide exhaled, a sign of energy use. They found the softer gum caused a 10 percent increase in the participants’ metabolic rates, while the stiffer gum caused a 15 percent increase. 

“I thought there wasn’t going to be as big a difference,” van Casteren tells the New York Times’ Kate Golembiewski. “Very small changes in the material properties of the item you’re chewing can cause quite substantial increases in energy expenditure, and that opens up a whole universe of questions.”

Compared to other mammals like cows, orangutans or especially pandas—which may spend a whopping 12 hours a day munching on bamboo—humans spend much less time masticating, averaging only about 35 minutes a day, writes Inverse’s Allison Parshall. 

Food consumed by our earlier Homo ancestors would have “certainly required a greater masticatory effort to orally process,” write the authors. But modern humans and our more recent predecessors cooked and used tools, which helped make chewing easier. As that happened, their tooth and jaw structure changed, becoming smaller than that of other primates, according to Science’s Andrew Curry.

Callum Ross, an anatomist at the University of Chicago who was not part of the study, tells Science he isn't convinced that energy use alone can explain the way our teeth and jaws evolved. 

“Natural selection probably cares more about not wearing your teeth out than energy efficiency,” he tells the publication. Still, he says, the new study is a starting point. 

Van Casteren wants his future research to look into how much energy chewing real food, rather than plain gum, exerts, and he also looks forward to uncovering more about human evolution, he tells the Times. 

“To know about the environmental and societal and dietary causes that led us to get here, it’s just infinitely interesting to me,” he says to the newspaper. 

Margaret Osborne is a freelance journalist based in the southwestern U.S. Her work has appeared in the Sag Harbor Express and has aired on WSHU Public Radio.

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