Xand van Tulleken and Helen Lawal oversee proceedings as three more pairs road test some of the most popular and talked about diets. Teaching assistants Sheila and Syrika have a week to trim down ahead of their end-of-term party, partners Greg and Nath go on six-week diets to slim down before Lincoln Pride and Becci and Cassie want to lose weight for a friend's wedding in three months. Xand asks if fizzy water can really make people gain weight and also goes on a keto diet.