A breakthrough study explains how chewing shaped human evolution

The first stage of digestion begins with chewing. In fact, it is such an important step that experts emphasize the importance of chewing many times. So, the act of chewing has a great role in our lives. But what if this action kick-started the evolution of our ancestors millions of years ago?

Scientists from Leiden University pursued the answer to this question and initiated a comprehensive research, initially reported by The New York Times. The results of the study were published on Wednesday in the journal Science Advances.

Using respirometry and electromyography of the masseter muscle, scientists found that chewing by human subjects represents a measurable energy sink. Moreover, it elevates metabolic rate above basal levels by 10 to 15 percent.

Six males and fifteen females between the ages 18 and 45 participated in the study. While the subjects sucked on soft or stiff chewing gum, the researchers took various measurements. The volunteers’ oxygen consumption, carbon dioxide production, and the activity of their masseter muscles were all measured using a customized hood and electrodes.

“When chewing the softer gum, the volunteers increased their energetic expenditure by an average of 10.2% relative to their basal metabolic rate (BMR). This rose to 15.1% above for the stiffer gum. BMR is the amount of energy that the body burns at rest each day,” told Paleoanthropologist Amanda Henry.

“What we discovered was that chewing food takes a lot of energy. And more importantly: the harder the food, the more energy it takes.”

Foods are softer today

As per The Scientist, the study started with a conversation over lunch. Paper co-author Adam van Casteren, an anthropologist at the University of Manchester in the UK, watched his coworker chew (and continue to chew) a salad and began wondering “how much more energy would be invested in eating a salad compared to eating a cooked meal?” So he and his colleagues designed an experiment to test just that.

Most foods today are processed and softer. But our ancestors had to eat seeds, nuts, and leaves. As a result, they spent much more energy chewing their food than modern humans.

“Modern humans are quite weird,” says van Castaren. “We don’t chew very much because we cook and process all of our foods before we eat. But our ancestors would have been spending a lot of time chewing.”

In addition to that, co-author of the study, Amanda Henry also said, “We assume that natural selection produced jaws, facial muscles, and teeth that make the chewing system as efficient as possible, thus minimizing the energy spent chewing food. We, therefore, think that how we humans chew today has been optimized by evolution.”

This discovery is expected to help better understand human morphology.

Study abstract:

Any change in the energetic cost of mammalian mastication will affect the net energy gain from foods. Although the energetic efficiency of masticatory effort is fundamental in understanding the evolution of the human masticatory system, nothing is known currently about the associated metabolic costs of chewing different items. Here, using respirometry and electromyography of the masseter muscle, we demonstrate that chewing by human subjects represents a measurable energy sink. Chewing a tasteless odorless gum elevates metabolic rate by 10 to 15% above basal levels. Energy expenditure increases with gum stiffness and is paid for by greater muscle recruitment. For modern humans, it is likely that mastication represents a small part of the daily energy budget. However, for our ancestors, before the onset of cooking and sophisticated food processing methods, the costs must have been relatively high, adding a previously unexplored energetic dimension to the interpretation of hominin dentofacial fossils.