This week Dr Christian Jessen tackles the eating habits of Amy-Jo, a superskinny undereater, who is due to spend five days in the 'feeding clinic' with 38½-stone Andy. The participants' attitudes towards food couldn't be more different, but they are both putting their health in danger. Amy-Jo may look perfect on the outside but her extreme exercise regime and diet, which restricts carbs, could lead to her body crumbling inside. To shock her into a new way of eating, she must gorge on the gigantic meals and colossal snacks of the biggest supersize of the series. Meanwhile Andy must learn to survive on the limited calorie intake of Amy-Jo. The aim is for them both to learn how they are affecting their bodies Journalist Anna Richardson tries another extreme diet, taking the star-studded route to dropping a dress size: living on tiny jars of baby food. She also meets former Liberty X star Michelle Scott-Lee, who spills the beans on the pressures for celebrities to be thin. Gillian McKeith has a shock in store for a team of large-bummed female rugby players from York as she continues her quest to reduce the nation's rears. Gillian also tests the knowledge of a bunch of London taxi drivers. With cheesy jackets, ploughman's and scampi and fries on the canteen menu, can they recognise a high calorie option when they see one?

• Liza Tarbuck
• Anna Ryder Richardson
• Gillian McKeith