Until fairly recently, the idea of listening to your gut was mostly metaphorical. The heart, lungs and liver are important to keep in good shape. But the stomach, intestines and colon? Surely they just keep chugging along, processing whatever you put into them, occasionally objecting, but basically doing their job. Well, not quite. Over the last five years or so, evidence has been piling up that the huge community of microorganisms – bacteria, viruses and fungi – that live in the gut affect everything from the immune system to mental health. We have learned that there are roughly 500m neurons in the human gut, alongside the 100bn in the brain, and research around the “gut-brain axis” – the biochemical signalling system that links your gastrointestinal tract and your central nervous system – suggests that signals go both ways between the two. Professional athletes, for instance, have more diverse gut microbiota than regular people, but it is becoming increasingly clear that the relationship is bidirectional – they might be better runners because they have more efficient gut bacteria, but doing more exercise is probably helping to keep the little chaps happy. “Having a healthy gut is part of being a healthy human on quite a number of levels,” ​​says Dr James East, a gastroenterologist at Mayo Clinic Healthcare in London. “Common signs that something is wrong with the system include persistent changes in bowel habits, abdominal pain, blood in the stool, weight loss and trouble swallowing. If any of these are happening you should seek medical help. But your gut microbiome might be important for lots of other things, such as putting on weight and depression. We can see correlations with that and we are already investigating whether altering or improving your microbiome might help some of these other health issues that are not classically associated with gut health. It’s an exciting field of research – the manipulation of the microbiome may be an opportunity to approach some of these challenging societal issues.” The gut seems to play a role in appetite, energy absorption and circadian rhythm, with one small study suggesting that diets can be effective depending on the different bacteria making up the microbiome. A relatively recent review of 21 studies on the subject, meanwhile, found 11 suggesting that regulating intestinal bacteria might have a positive effect on anxiety. So how do you give your gut the best chance of keeping you in shape? “From a dietary perspective, there are straightforward things that you can do such as eating a more Mediterranean-style diet – less processed meat, more olive oil, fish, nuts, fruits and vegetables,” says East. “Having enough fibre in your diet, drinking enough water and taking exercise can all improve gut motility, while eating a diverse range of foods is also helpful.” Gut motility, or how fast food transfers through the whole system, seems to be a good indicator of your microbiome’s health overall, with shorter “transit” times for food generally suggesting a healthier gut. If you want to improve the overall diversity and health of your gut bacteria, the best nutritional bang for your buck is to add prebiotics and probiotics to your diet from whole foods – the former will encourage existing gut bacteria to multiply by giving them something to feed on, while the latter are live bacteria that will top up your stores. Prebiotics are easily increased by adding more garlic, onions, legumes, beans and berries to your regular diet. Probiotics are another matter – some options include kimchi (try this in quesadillas), sauerkraut (a spoonful goes nicely with scrambled eggs) or kefir (perfect as a post-gym drink). It is probably a good idea to avoid processed foods if you can, but your gut’s relationship with booze is more complicated – in one study, gin decreased the amount of “good” bacteria in subjects, while moderate red wine intake seemed to increase it. And, as we have already seen, getting enough exercise and sleep seem to be important for good gut health, but the relationship goes both ways – so by taking care of your gut’s feelings, you can trust it to look after you.