At just 6 stone 10lbs, 19-year-old Tatiana Moxey is extremely underweight and desperate for people to stop asking her if she's got an eating disorder. Weighing in at 23½ stone, jazz singer Sandra Andrew is a late-night food lover, enjoying home-cooked West Indian food through the day before feasting on junk food all night long. In the feeding clinic, under the supervision of Dr Christian Jessen, Tatiana and Sandra take part in an extreme diet swap to fatten up skinny Tatiana and slim down overweight Sandra. Meanwhile, size 14 journalist Anna Richardson immerses herself into the world of serial dieters and attempts to drop a dress size or two by following their faddy diets and lifestyle regimes. This week she looks behind the glamorous façade of modelling and exposes the body-abusing methods some models use to stay skinny as she embarks on an extreme apple-only 'model' diet. And it's no wonder we're obsessed with the size of our bottoms: Britain has the biggest bums in Europe; so Gillian McKeith is on a nationwide campaign to reduce the size of our rears. And with the help of 101 women, the latest treatments, hi-tech gadgets and machinery that claim to achieve a perfect rear are put through their paces. This week a group of Nottinghamshire lasses are lassoed to horse-riding simulators to gee up their chances of success. And if you wise up to calorie content you can still indulge without the bulge. Gillian McKeith heads to Billingsgate Market to find out if the fishmongers of London know a high-calorie breakfast when they see one.

Fussy eaters put up a food fight in the feeding clinic as Superskinny Yasmin Smith is forced to swallow a gargantuan diet of snack foods and diet drinks, while Supersize Darryl Weston weighing in at a whopping 33 stone and one pound suffers on Yasmin's lactose, wheat, sugar and fat free diet. Dr Christian Jessen referees the match. Journalist Anna Richardson takes the nip and tuck route to slimming by investigating the world of cosmetic treatments, but she meets with unforeseen complications during the procedure. Gillian McKeith is sent to Coventry as part of her nationwide campaign to turn bountiful bottoms into bums of steel. This week can the personal services of a gym bunny reduce their rears? And there's no need to battle the bulge if you know the calories of your favourite foods. With Cornish pasties, chicken salad and ham rolls on offer, do the market traders of St Albans know a high calorie lunch when they see one?

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?

Tipping the scales at just over six stones, 41-year-old Elizabeth Young thinks she's found the elixir to eternal youth: an extremely disciplined diet. She exists on a radical diet of Brazil nuts, rice, garlic and not much else. In the feeding clinic, Dr Christian Jessen, begs to differ and has the challenge of persuading her that her lack of eating is doing the exact opposite; it's prematurely ageing her. Dr Jessen's prescription is a short, sharp shock, a week of eating the food of 34 stone 9lbs supersized milkman Stefan Ginesi, the fattest contributor of the series. The Northern Irish 'carb junkie' lives on potatoes and Irish stew and is keen to lose weight to start dating and get involved in a relationship. Into the fourth week of her diet, journalist Anna Richardson goes nil by mouth when she swaps food for diet pills. On the way she meets Denise Townsend, whose prescription pills left an unsightly and permanent residue in her pants… and her toilet. And more alarmingly she encounters two young pill poppers whose cocktail of diet pills is potentially seriously damaging their health. Corporal Gillian McKeith gives a posse of Portsmouth girls their marching orders as they attempt to reduce their rears with the help of Masai technology, a trainer designed to get the wearer to copy the tribe's long-distance walking technique. And do the high-rollers at the dogs know a high calorie takeaway when they see one? With pizza, a burger and an Indian on offer which one is odds on favourite for a feast? Gillian McKeith reveals how to indulge and avoid the bulge.

Dr Christian Jessen comes face to face with twenty-six-year-old Kevin Calladine from Brighton who hasn't had a decent meal since he left home. Short on time and money, his weight has plummeted to just 8 stone 5lbs, two and a half stone underweight, which is no great surprise because Kev lives on a diet of coffee and cigarettes for breakfast, pre-packed sandwiches for lunch and a liquid dinner of orange juices. Meanwhile, supersized super-eater Julie Mead from Essex weighs in at 26 stone 6lbs. Julie hopes some motherly love will help fatten Kev up while she learns to curb her excessive food consumption. Journalist Anna Richardson continues her weight-loss crusade, hoping that hypnosis will help her drop a dress size. Surfer girl Gillian McKeith dons her wetsuit to get some Welsh rare-butts to reduce their rears. And how to have your cake and eat it: with three posh puddings on offer – Pavlova, Belgian chocolate cake and apple tart – can the horsey set guess a high-calorie pudding when they see one? Gillian offers some low-calorie alternatives.

In the feeding clinic this week with Dr Christian Jessen are two women at opposite ends of the weight spectrum but with one thing in common: they both want to look wonderful in their wedding dresses. Wafer-thin Jenette Nolan from Lancashire refuses to marry her husband until she can fill her wedding dress but she's got a long way to go. Weighing just 6 stone 8lbs, she's two stone underweight. Meanwhile Rosemarie Palmer, who lives on the Isle of Man, is hoping that a week's food swap will kick start her weight-loss plan to get from over 21 stone to a size 14 in time for her wedding this summer. Meanwhile, journalist Anna Richardson looks into the dark world of extreme dieting. She meets Lisa Bond who became partially blind by taking the radical decision to stop taking insulin in order to lose weight. Anna also talks to ex-Big Brother housemate Nikki Graham about the extremes she has gone to in order to stay thin. And when it comes to reducing the size of the nation's rears, Gillian McKeith is cleaning up the act of a group of Brummie bottoms with a device that promises to vacuum away the fat. And after dealing with the ladies of Birmingham Gillian's off to test some ten-pin bowlers on what they know about the calories in some typical party food.

Dr Christian Jessen faces a bumpy ride this week in the feeding clinic as superskinny size zero Louise Sapsford, who clocks in at 6 stone 2lb, faces up to supersize 28 stone 13 pounder Desroy Gordon's challenging diet of non-stop take-aways. Louise comes to terms with the fact that size zero is not a good look and changes her eating habits for good. Stuffing herself with Desroy's gigantic meals and a relentless run of take-away dinners teaches Louise she can eat more than the tiny meals she never normally finishes. Journalist Anna Richardson nips across the pond to New York City where she discovers the very latest fat-busting techniques, including cheerleader aerobics! Gillian McKeith has a powerful arse-busting technique in store for some London lasses as she continues her quest to reduce the nation's rears. For this week's Extra Helpings Gillian finds out if a bunch of jive dancers know their calories as well as their moves as she offers them a variety of romantic dinners for two. Can they tell which dishes they can dine out on without building up their love handles?

Long and lanky, 22-year-old Alex Law from Stockport hits the scales at just over ten stone because he barely eats a meal. Tired and exhausted he lives on a diet of caffeine pills supplemented by stodgy cakes and snacks despite holding down the physically demanding job of a plasterer. Dr Christian Jessen decides to hit him where it will hurt most with a stiff warning about his manhood. His diet swap partner Tracy Morgan from Wales has a mouth that's constantly on the move. If she's not talking at the call centre where she works she's snacking, just like Alex, but the trouble is she's snacking before, after and in between her already substantial daily meals which has caused her weight to soar to nearly 20 stone. Deprived of the meals and forced to eat just Alex's snacks she soon realises where she's going wrong. Journalist Anna Richardson meets Isabelle Caro, the actress who unwittingly found herself a worldwide celebrity as the star of a media campaign to highlight the shocking affects of anorexia. And for the first time in her life Gillian McKeith pigs out as she gets a group of ladies from Basingstoke to reduce their rears with a workout at a pig farm followed by trying out the bum-shrinking effects of mud-packs. Does mum know best when it comes to counting calories? The nation's favourite family meals are checked out by supermarket check-out girls for their highest calorie content as Gillian dishes up spaghetti Bolognese, good old-fashioned sausage, mash and gravy, and a traditional roast beef meal.