Many of us take dietary rules for granted such as eating little and often, not skipping meals and keeping a check on our calorie intake. But genetic epidemiologist Professor Tim Spector argues we need to re-evaluate what we think we know about a good diet: diversity in both the types of food we eat and in the unique mix of microbes we nurture in our gut is the most important factor for health.In a multi disciplinary career following early training as a rheumatologist, Tim founded the UK Twins Registry at Kings College London to unravel the extent to which genes contribute to a vast range of human conditions and diseases. But the puzzling differences he observed in identical twins would fuel his current research on the gut microbiome and the discovery that each of us has a unique mix of gut bacteria – in effect a chemical factory that dictates our highly individual responses to different foods. Tim tells Jim Al-Khalili how his research has evolved to successfully develop a new scientific approach to personalised nutrition – through technology that during the pandemic has famously been pressed into service to track Covid symptoms across the UK, and that’s now revealing how a diverse diet has huge implications for Covid-19 outcomes. Producer: Adrian Washbourne