Professor Tim Spector has spent three decades asking: why do people respond so differently to the same food? As a genetic epidemiologist at King’s College London and founder of the Twins UK registry, he built one of the world’s richest long-term datasets on health, genetics, and environment. The insight that our gut microbiome may matter as much as our genes when it comes to metabolism and disease risk, helped to launch ZOE, a science-led nutrition company combining large-scale research with consumer testing to personalise diet advice. ZOE’s studies, including the large Predict trials and the widely used Covid Symptom Study app, have brought epidemiology into the era of digital health and citizen science. Tim was awarded an OBE for services to medicine. This episode explores the science behind the microbiome revolution and what personalised nutrition might mean for the future of public health.