If you want to learn more about what’s going on in your gut, the first step is to turn your poo blue. How long it takes for a muffin dyed with blue food colouring to pass through your system is a measure of your gut health: the median is 28.7 hours; longer transit times suggest your gut isn’t as healthy as it could be. We are only now beginning to understand the importance of the gut microbiome: could this be the start of a golden age for gut-health science?

“The gut microbiome is the most important scientific discovery for human healthcare in recent decades,” says James Kinross, a microbiome scientist and surgeon at Imperial College London. “We discovered it – or rediscovered it – in the age of genetic sequencing less than 15 years ago. The only organ which is bigger is the liver.” And, for all that the internet may be full of probiotic or wellness companies making big health claims about gut health, “We don’t really know how it works,” he says. At the risk of sounding like the late Donald Rumsfeld, there’s what we know, what we think we know, and an awful lot that we don’t yet have a clue about.