About 10% of the calories consumed over the course of the day are expended on digesting, absorbing, metabolizing, and eliminating that food. According to a new study, you can add another 1% to that — the energy we burn in the act of chewing food. That might not seem like a lot, but it’s more than previously expected, and scientists now think mastication likely played a major role in shaping the kind of faces humans have today.
Around 4 million years ago, our earliest ancestors, such as Ardipithecus and Australopithecus, ate tough plant foods, such as seeds, nuts, tubers, and fibrous leaves that would have large jaw muscles and cheek teeth to break down. As such their faces were broad and deep to accommodate massive muscle attachment areas.
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Although energy consumed on chewing is significant, early humans must have burned even more calories in our lineage’s distant evolutionary past. According to one estimate, humans only spend 7 minutes a day chewing food, whereas mountain gorillas can spend up to 90% of their waking time masticating food. If early human ancestors were more like gorillas than us, they also must have spent copious amounts of energy on chewing. From this standpoint, modern humans are incredibly efficient at squeezing every calorie out of the food we eat to transform that energy into more useful work.
