Tim Spector is a professor of genetic epidemiology at King's College London and honorary consultant physician at Guy's and St Thomas' Hospitals. He is a multi-award-winning expert in personalised medicine and the gut microbiome, and the author of four books, including the bestselling The Diet Myth. He appears regularly on TV and radio around the world, and has written for the Guardian, BMJ, and many other publications. He is the lead researcher behind the world's biggest citizen science health project, the COVID Symptom Study app. This free tool has been used by nearly 4 million people in the UK, US and Sweden to diagnose themselves without testing. It has confirmed new symptoms and risk factors for the virus, allowing scientists to monitor its progress and warn health authorities.