Dr Xand van Tulleken and dietician Hala El-Shafie ask ordinary Brits to road test some of the most popular and talked about diets out there, and to then give viewers the lowdown on how the diets worked for them. CafÚ cook Stacie Stewart helps the volunteers to turn their diets into delicious dishes. This time, Daria and Emma have seven days to slim down for a birthday bash; bridesmaids Emma and Elisa go on six week dieting plans for a forthcoming wedding; and entrepreneurs Dom and Adam want to slim down for a corporate summer party in four months. To find out how fasting affects body and mind, Xand goes on an extreme 'water-only' fast, and investigates if so called 'zero calorie' and 'negative calorie' foods really exist.