Humans take 35 minutes to chew. Every year, that adds up to more than a week. Chimps chew for 4.5 hours a day, and orangutans chew for 6 hours a day.
Our chewing habits are different from those of our closest relatives. A study published Wednesday in the journal Science Advances explores how much energy people use while chewing.
In addition to keeping us from swallowing, chewing makes it easier for us to digest food. The act of chewing requires us to burn a lot of calories. Humans adapt to their teeth, jaws and muscles.
Adam van Casteren, an author of the new study and a research associate at the University of Manchester in England, says that scientists haven't looked too deeply into the energetic costs of chewing because it's a thin slice compared to other activities. He wanted to find out if chewing could be a big part of evolution.
To measure chewing energy, Dr. van Casteren and his colleagues fitted study participants with plastic hoods that looked like astronauts helmets. Oxygen and carbon dioxide can be measured from breathing. Gas exchange can be used to measure how much energy is taken up by a process. The subjects were given chewing gum.
The gum bases they chewed were odorless and tasteless. The researchers wanted to make sure they were only measuring the energy associated with chewing and not the energy of a stomach preparing for a meal.
The test subjects chewed two pieces of gum for fifteen minutes each. Researchers were shocked by the results. When the participants were resting, the softer gum increased their metabolism by 10 percent, while the harder gum increased it by 15 percent.
There wasn't going to be a big difference. Changes in the material properties of an item can lead to substantial increases in energy expenditure, and that opens up a lot of questions.
The findings suggest that the cost of chewing may have been an important factor in the evolution of our species. Making food easier to process through cooking, mashing food with tools and growing crops for eating might have lessened the evolutionary pressure to be a super-chewer. What our faces look like may be influenced by our chewing needs.
Justin Ledogar, a biological anthropologist at East Tennessee State University who was not involved with the study, said that they haven't been able to figure out why the skull is funny. Our facial skeletons are built with small jaws, teeth and chewing muscles compared to our relatives. He said that this reflected a reduced reliance on chewing.
He said that our faces and jaws allow us to bite more quickly. The process of feeding is less expensive because of it. Humans were able to chew smarter. Dr. van Casteren hopes to learn more about how humans evolved through his research.
He said that he was interested in knowing about the environmental and societal causes that led to us getting here.
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