How much energy do we use when chewing

In order for us to better digest our food, we chew it before swallowing it. But the chewing process itself also costs energy. A new study has now measured energy consumption during chewing for the first time. Accordingly, the activity of the masticatory muscles increases our base energy consumption by up to 15 percent, depending on how hard the food is. While these costs are negligible for modern humans, they may have played a role for our early human ancestors, who had yet to cook.

Chewing food is an important step in the digestive process. The food is already broken down in the mouth in such a way that the nutrients it contains are more readily available for additional digestion steps. Although using jaw muscles also costs energy, chewing has become a more energy-efficient alternative to swallowing larger pieces in the course of evolution. But how much energy does chewing actually cost?

Chewing gum for science

A team led by Adam van Kastern of the University of Manchester investigated this question. To do this, the researchers asked 21 people to chew gum in a lab. To ensure that the results were distorted as little as possible by any digestive processes stimulated by chewing, the researchers selected tasteless and odorless gum with two different degrees of hardness. They also instructed the participants not to eat anything from the evening before the experiment. In the lab, they first measured individuals’ basal metabolic rate for 45 minutes while they were lying on the couch. Depending on body weight and gender, this averaged 4.27 kilojoules per minute, or 1.02 calories, in the test group.

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Next, the researchers asked the participants to chew hard or soft gum for 15 minutes and measured how their basal metabolic rate changed. The result: “Chewing either gum significantly increased energy expenditure compared to the basal metabolic rate, with harder gums requiring more energy than softer gums,” the researchers report. When chewing soft gum, the basal metabolic rate increased by about 10% to 4.69 kilojoules per minute (1.12 calories), while chewing hard gum increased by up to 15% to 4.91 kilojoules per minute (1.17 calories).

Related to human evolution

However, anyone hoping to become slim by chewing should be disappointed by the researchers: “Although chewing a test substrate results in a significantly higher energy rate compared to the base metabolic rate, the daily costs of chewing are relatively low. , even with the longest chewing times reported in humans which are well below 1% of basal metabolic rate.” According to previous studies, people today chew hardly more than half an hour a day. In addition, we as modern humans eat cooked food that we previously worked on using utensils. So we don’t chew as much as our early relatives and ancestors did,” says Van Kastern.

On the other hand, modern apes and perhaps our early ancestors may have spent more time chewing. Studies show that daily chewing times are about 4.5 hours for chimpanzees and up to 6.6 hours for orangutans. “These chewing habits are probably more representative of the amount of chewing work that early humans had to do,” the researchers wrote. In addition, the available food was probably much harder than all of the gum used in the experiment, which could increase the energy costs of chewing. Thus, more efficient chewing and emerging technical possibilities to facilitate food chewing and digestion may have a critical role in human evolution.

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Source: Adam van Casteren (University of Manchester, UK) et al., Science Advances; doi: 10.1126/sciadv.abn8351

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