Chewing consumes a surprising amount of energy

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Christophe Intagliata: When paleoanthropologists have lunch with biomechanists…well, sometimes the conversation can get quite technical.

Adam Van Casteren: Some of us would have cooked potatoes and some would have raw salads… this got us thinking not only how long does it take to get through your food, but does it expend more energy than those who eat cooked food.

Intaglio: Adam van Casteren from the University of Manchester says, thankfully, there is a machine to measure this. It’s a transparent chamber that you slip over your head – looks like an astronaut helmet. And it measures the oxygen you breathe in versus the carbon dioxide you breathe out…an indicator of how much energy you’re burning.

Intaglio: Van Casteren and his colleagues had 21 volunteers sit in this device for 45 minutes, just to get a baseline on their metabolism. Then they gave them flavorless gum to chew, for 15 minutes at a time.

Van Casteren: If you ever have to chew something for 15 minutes, that’s a lot longer than you think. And sometimes we had to remind people… ‘keep chewing!’

Amanda Henry: “And boredom is the key point here – like you’ve been chewing gum for too long and it’s lost its flavor and it’s just this stuff…it’s what the participants were chewing.”

Intaglio: Co-author Amanda Henry from Leiden University in the Netherlands explained that rather than cooked potatoes and raw salads, they needed something tasteless and odorless. Because anything appetizing would trigger a chain of digestive reactions. Saliva and digestive juices would start flowing…and overwhelm metabolic metrics related to chewing.

Intaglio: And those measurements were significant — it turns out that chewing gum increased the volunteers’ metabolic rates by 10% above baseline. A stiffer gum accelerated the metabolic rate by 15%.

Van Casteren: Such a big difference on such a small change in the mechanical properties of the chewing substrate is what opened my eyes and made my jaw drop a bit no pun intended.

Intaglio: And he says energy expenditure might increase even more for harder foods, like carrots, nuts and seeds. The results are in the log Scientists progress. [Adam van Casteren et al, The cost of chewing: The energetics and evolutionary significance of mastication in humans]

Intaglio: Now, before you give up on your workout routine, keep in mind that chewing gum boosts metabolism in much the same way as if you were at a computer…or reading a book.

Henry: It’s not going to the gym and lifting weights, is it? You don’t build giant muscles with chewing. But it’s still a process that can eat up a lot of your energy expenditure during the day.

Intaglio: And while humans don’t spend a lot of time chewing…especially considering the cooked and processed foods we eat…I mean how long does it really take to chew a chicken nugget? The same is not true for our primate cousins. Orangutans and gorillas spend up to six and a half hours a day chewing! And it’s possible that our human ancestors did too.

Van Casteren: This is something that natural selection can work on, it can change tooth morphology or muscle architecture to increase the energy you get from your food and it can give you a competitive advantage over your neighbor who sucks to chew or something like that.

Intaglio: The researchers say the work could give scientists a new evolutionary lens through which to interpret fossil remains…especially the body parts most often left behind…teeth and jaws.

[The above text is a transcript of this podcast.]

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