Chewing Grass

Humans Chewing Up Energy When We Eat

Believe it or not, the amount of energy we’re chewing up when we eat is both significant and important to understand. It’s significant because chewing can raise the rate at which our bodies burn energy by 10 to 15 percent. Just last week, Adam van Casteren published a paper quantifying this for the first time in Science Advances.

It’s important because it might help explain how humans evolved by learning to process their food so that they could spend less time and energy eating it. It might even have implications for understanding the contribution of ultra-processed foods to weight gain and obesity.

A Small, Carefully Controlled Study

Van Casteren et al used indirect calorimetry to precisely measure the metabolic cost of chewing in 21 subjects. They also used electromyography to document how these subjects activated their masseter muscles for this energy expenditure.

They measured basal metabolic rate for each of these people, as well as the energy they used for chewing two different flavorless gums for 15 minutes each. The only difference between the two gums was that one was softer and easier to chew. The other was stiffer and harder.

That difference meant that people used 50 percent more energy to chew the stiffer gum. This matters for understanding human evolution and the important milestone of humans learning to cook and process their food to make it easier to eat. Van Casteren explains that humans put much less energy into chewing:

“Modern humans are the weird ones. We have really soft foods and low chewing times .Reducing the amount of energy you’re spending on chewing is another element to these milestones in human evolution, or in agriculture, where you’re selecting foods that are less fibrous or chewy.”

We spend about 35 minutes daily chewing our food – it adds up to more than a week every year. But other primates spend much more time and energy on this essential task. Mountain gorillas can spend up to 90 percent of their waking hours chewing. Our jaws are physically very different from other apes and it may be that reduced demand for chewing helps to explain this.

Let’s be clear. The importance of this study is not the effect size of chewing a piece of gum for 15 minutes. It’s not large. What’s important is that it provides clues for answering other questions.

Eating Processed Food More Easily and Quickly

In a 2019 study of minimally processed versus ultra-processed foods, Kevin Hall and colleagues found that ultra-processed foods caused people to eat about 500 calories per day more than a similar diet of minimally processed foods. That result was a surprise to Hall and so scientists want to know what explains this difference.

One explanation might be that the ultra-processed food was easier to eat – reflected by the fact that people ate that food faster than they ate the minimally processed foods. This study provides one more clue and some food for thought.

So yes, the energy that goes into chewing is noteworthy, measurable, and may be important for understanding how our food environment has changed to prompt us to eat more and do it more easily.

Click here for the study by van Casteren et al, here, here, and here for further perspective on it. For the study by Hall et al on ultra-processed food, click here.

Chewing Grass, photograph by Ivan Radic, licensed under CC BY 2.0

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August 22, 2022