World-leading microbiome scientist and surgeon James Kinross shows us how everything from exercise, sleep and diet through to antibiotics and ageing are directly impacted by the state of our microbiome. He introduces us to the microbiome, a vast genetic universe of ‘dark matter’ – bacteria, yeasts, viruses and parasites – living inside us, which adapts with us as we age and influences how we think and feel, our sex lives and even how fast we run. Kinross is a senior lecturer in colorectal surgery and consultant surgeon at Imperial College London. He talks to neuroscientist Dr Hannah Critchlow.