Dr Michael Mosley reunites five volunteers, whose health he helped transform in Lose a Stone in 21 Days with Michael Mosley, in a bid to myth-bust some of the common misconceptions around healthy weight management. Using cutting-edge tests and technology to illustrate that the calories our volunteers actually need day to day, could be different to the NHS's recommended daily amounts, the show investigates whether weight loss inevitably leads to putting weight back on again, and explores whether exercise is as helpful as we think. There is also bespoke advice to each volunteer on how to achieve a healthy weight for the long term.