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.
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.