The cost of chewing: the energetics and evolutionary significance of mastication in humans

Abstract

Mammalian mastication represents a vital initial step in digestion with any change in its relative energetic cost detracting from the net energy gain from foods. Although the energetic efficiency of masticatory effort is one of the fundamental concepts through which the functional morphology and evolution of the human masticatory system is explored, nothing is known currently about the associated metabolic costs and how this is influenced by the item being chewed. Here, using respirometry and electromyography of M. masseter, we demonstrate that chewing by human subjects represents a measurable energy sink. Chewing a tasteless odorless gum elevates metabolic rate by 10-15% above basal levels. The 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 novel energetic dimension to the interpretation of hominin dentofacial fossils.