Doctor and dietician Michael Mosley puts five volunteers on a low-calorie diet to help get their health back on track after the UK's Covid-19 lockdown. In the first episode, Michael runs a series of tests to find out just how badly lockdown has affected his volunteers' health, before creating a bespoke diet plan for the 21 days. He also tests misconceptions of what a healthy BMI looks like, and explores the cutting-edge research which indicates ties between BMI and survivability from Covid-19