Chewing burns more calories than you think, and may have shaped our evolution science

When it comes to ways to burn calories, few people think about chewing. But about 3% of the daily energy we burn comes from munching on gum, gristle and other treats, according to a new study, and maybe more if you like salads and celery sticks. That’s a lot less than walking or even digesting, but it may have been enough to reshape the faces of our distant ancestors.

The study adds concrete data to the debate about why human jaws are so different from those of our distant ancestors and modern primates, says Callum Ross, an anatomist at the University of Chicago who was not part of the study . “That gives us a number we can start working with.”

Scientists have long suspected that our jaw size and tooth shape evolved to make chewing more efficient. As our hominid ancestors shifted their diet to easier-to-chew foods and developed technologies such as chopping and cooking to reduce the time and effort spent on chewing, the shape of the jaw and teeth also changed. change, was reduced compared to other primates. But without knowing how much daily energy we expend chewing, it is difficult to determine whether energy conservation was also a factor in driving these evolutionary changes, says Adam van Casteren, a biological anthropologist at the University of Manchester.

So in the new study, van Casteren and his colleagues put 21 men and women in a bubble-like helmet. The device measured the amount of oxygen they consumed and carbon dioxide (CO2) exhaled. The scientists then gave the participants a flavorless, odorless, calorie-free gum to chew for 15 minutes.

Using a special helmet, the researchers measured the amount of energy the volunteers used chewing.Adam van Casteren

While chewing, CO2 the volunteers’ breathing levels increased, indicating that their bodies were working harder. (Because the gum had no smell, taste or calories, it did not activate the digestive system, which also uses energy.) When the gum was soft, the volunteers’ metabolism increased by an average of 10%; a stiffer gum required 15% more energy than at rest. “It’s not huge, but it’s still important,” says study co-author Amanda Henry, an archaeologist at Leiden University.

Overall, chewing gum accounted for less than 1% of participants’ daily energy budgets, the team concluded today. Advances in Science. But chewing gum in a lab was essentially a proof of concept: Before the advent of cooking and the use of tools, early humans likely spent much more time chewing. If ancient peoples had spent as much time chewing gum as gorillas and orangutans do, the authors estimate that they could have consumed at least 2.5% of their energy budget chewing. “If you ate harder foods and chewed longer, you’d end up with a much larger proportion of your total energy expenditure,” says Henry.

The findings were a surprise. Henry says that even some of his collaborators were skeptical that the energy needed to chew would be enough to measure in the lab. “I think it’s a great study. It shows that a measurable amount of energy is being used,” says Ross.

The finding supports the idea that more efficient chewing, adapted to diet, may have been an evolutionary advantage, Henry says. “By saving energy in the chewing category, you have more energy to spend on other things, like rest, recovery and growth.”

Calculating the energetic cost of human chewing could also provide insight into the evolutionary strategies of other hominids. For example, Australopithecus— a hominid that lived in Africa between 2 and 4 million years ago — had teeth with chewing surfaces four times larger than modern humans and massive jaw muscles. They must have expended more energy chewing, and the new study is a first step in figuring out how much. “Presumably … they were taking advantage of very energy-dense foods,” says Henry. “We have the first evidence to explain this pattern.”

Still, Ross isn’t convinced that energy alone can explain the way jaws and teeth evolved over time. Other factors, such as the shape of the jaw that minimized tooth breakage or wear, for example, may have been more important. “Natural selection probably cares more about not wearing down your teeth than about energy efficiency,” he says; an animal without teeth would quickly run out of energy.

Compared to Australopithecus or primates living today, humans are an outlier: some estimates suggest we only spend 7 minutes a day chewing. By contrast, mountain gorillas can spend up to 90% of their waking time chewing, as do ruminants such as goats and cows. “Modern humans are the odd ones out. We have very bland foods and low chewing times,” says van Casteren. “Reducing the amount of energy you spend chewing is another element of these milestones in human evolution or agriculture, where you select foods that are less fibrous or chewy.”

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