Dr Xand van Tulleken and Dr Helen Lawal challenge three pairs of friends to try out the latest popular diets, while cook Stacie Stewart demonstrates some healthy recipes. Sophie and Zoe give the Citrus Diet and the Sexy Pineapple Diet a road test, Barbara and Denise spend six weeks on the Summer Salad Diet and the Summer Sandwich Diet ahead of their holiday in Ibiza, and Theo and Ervis take on the Greek Island Longevity Diet and the South American Diet so they can lose weight in time for a pool party.