Can you taste the difference between a calorie-laden sugar and a zero-calorie sweetener? Specialised cells in your gut can, according to experiments in mice. These cells tell the brain whether a sugar or sweetener has been ingested within milliseconds.

Research in the 1950s revealed that food doesn’t need to pass through the mouth to stimulate a response from the brain. Mice respond to food rewards when they are put directly into their stomachs, too. More recent studies have found that mice favour sweet foods even when their taste …