Xand van Tulleken, dietician Hala El-Shafie and cook Stacie Stewart oversee proceedings as three more pairs road test some of the most popular and talked about diets. AK and Bethany have two weeks to slim down for an evening of speed dating, Gemma and Charlotte want to lose weight for their school reunion in six weeks, and married couple Si and Simon aim to shed the pounds for Manchester Pride in four months' time.