Engineering approaches to chewing and digestion.

The guts of people and animals function like industrial chemical plants. They are assemblies of tubes and tanks in which foods are hydrolysed by enzyme-catalysed reactions, or fermented by microorganisms. Raw materials enter at one end, waste matter is voided at the other, and valuable products are abstracted on the way. A mill at the entrance end reduces the raw materials to small fragments, enabling the reactions to proceed faster. This paper shows how ideas from chemical engineering are guiding research on the gut, giving much clearer understanding of how foods respond to chewing, and of how guts are designed to process different foods. We will discuss the teeth as a grinding mill, and the digestive tube as a chain of chemical reactors.