Dr Xand van Tulleken and Dr Helen Lawal ask ordinary Brits to test some of the most popular and talked about diets and give viewers the lowdown on how the diets performed for them. Café cook Stacie Stewart helps the volunteers to turn their diets into delicious dishes. Katy and Emily have two weeks to slim down for Katy's summer wedding, Valenta and Praise go on six-week dieting plans to lose weight for a beach holiday and Johnny and Joe want to slim down for a pool party in four months' time.