Chewing burns more calories than you think – and can shape our growth 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 chewing gum, gristle and other stuff, a new study finds — and maybe if you’re partial to lettuce and celery stalks. That’s much less than walking or digesting, but it may have been enough to reshape the faces of our distant ancestors.

The study adds solid data to the debate about whether human primates differ from our distant ancestors and modern primates, says University of Chicago anatomist Callum Ross, who was not part of the study. “That gives us a number we can start working on.”

Scientists have long suspected that the shape of our jaws and the shape of our teeth evolved to make chewing more efficient. As our hominid ancestors developed techniques such as chewing and cooking to make their diet easier to digest and reduce the time and effort involved in chewing and cooking, the shape of the jaws and teeth also changed, shrinking compared to other primates. But because we don’t know how much energy we expend daily on chewing, it’s difficult to determine whether energy conservation was also a factor driving these evolutionary changes, says Adam van Castren, a biological anthropologist at the University of Manchester.

So in a new study, van Casteren and his colleagues put 21 men and women into bubble-like helmets. The device measures the amount of oxygen they consume and the amount of carbon dioxide (CO2) They sighed. Then, the scientists had participants chew a tasteless, odorless, calorie-free gum for 15 minutes.

Using a special helmet, the researchers measured how much energy the volunteers used to chew.Adam Van Castren

During chewing, CO2 The volunteers’ breath levels increased, indicating that their bodies were working harder. (Because the gum had no smell, taste or calories, it did not trigger the digestive system, which also consumes energy.) When the gum was soft, the volunteers’ metabolism increased by an average of 10%; A hard gum requires 15% more energy than a relaxed one. “It’s not huge, but it’s still significant,” says study co-author Amanda Henry, an archaeologist at Leiden University.

Overall, chewing the gum represented less than 1% of the participants’ daily energy budget, the team concluded today. Science advances. But chewing gum in the lab was essentially a proof of concept: Before the advent of cooking and tool use, early humans probably spent a lot of time chewing. If ancient humans spent as much time chewing gum as gorillas and orangutans, the authors estimate that they would spend at least 2.5% of their energy budget on chewing. “If you’re eating hard foods and chewing for a long time, you end up with a much larger proportion of total energy expenditure,” says Henry.

The conclusion came as a surprise. Henry says even some of her colleagues were skeptical that the energy required to chew would be enough to measure in the lab. “I think this is a great study. It shows that measurable energy is used,” says Ross.

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

Calculating the energy cost of human chewing may also provide a glimpse into the evolutionary strategies of other hominids. for example, AustralopithecusHominid living in Africa between 2 million and 4 million years ago had teeth four times larger than those of modern humans and jaw muscle chewing surfaces. They must have expended more energy chewing, and the new study is the first step in calculating just how much. “They were probably … taking advantage of the more energetically expensive food,” says Henry. “We have the first piece of evidence to explain that pattern.”

Still, Ross isn’t convinced that energetics alone can explain the way jaws and teeth have evolved over time. Other factors—like jaw size that reduces tooth breakage or wear, for example—may be more important. “Natural selection cares more about not putting your teeth out than energy efficiency,” he says; A toothless animal quickly depletes its energy.

When compared Australopithecus Or primates living today, humans are an outlier: some estimates suggest we spend only 7 minutes a day chewing. In contrast, mountain gorillas can spend up to 90% of their waking hours chewing, as do ruminants such as goats and cows. “Modern humans are weird. We have really soft foods and less time to chew,” says van Casteren. “Reducing the amount of energy you’re expending on chewing is another element of these milestones in human development, or in agriculture, where you’re choosing foods that are less fibrous or chewy.”

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