Weighing in at just 6 stone 8 pounds is superskinny working mum Gillian. The 24-year-old Inverness nurse is so busy caring for others she's forgotten how to look after herself and her weight has plummeted.

Her polar opposite is another nurse, 26-stone self-confessed foodie Philippa, whose typical daily supersize menu includes a generous breakfast, followed by burger and fries, Yorkshire pudding and shepherd's pie.

Both women get shocking wake-up calls: Gillian discovers the devastating effects her diet has had on her body and Philippa comes face to face with the consequences of a lifetime of overeating when she meets Lisa, a woman about to undergo life-threatening weight-loss surgery.

Meanwhile, Anna Richardson travels to LA to investigate the continuing obsession with thinness. Back in the UK, she launches her very own Flab Fighters club and teaches a group of serial failed dieters from Newport how to indulge in their favourite treats and still lose weight.

Checking into the feeding clinic is marathon-running, superskinny Kim Fawke. Following a stressful divorce, her weight has plummeted to just over six stone.

In her race to get her relationship with food back on track, she's joined by supersized scoffer and takeaway queen, 23 1/2 stone Trudy Alexander.

Meanwhile, Anna and her Flab Fighters club swap gorging on cheddar for a hike in the Cheddar Gorge.

And four young women in the grip of the eating disorder anorexia nervosa reveal their extreme eating habits, and are forced to discuss the causes, symptoms and anxieties around their distorted relationship with food.

Featherweight father-of-two Colin Hunt barely tips the scales at nine stone by living on chocolate and little else.

Joining him on the five-day diet swap is a supersizer twice his weight, Tracey Hibbert, who binges on bread. Her post-baby weight has rocketed to 18 and a half stone and she is desperate to lose the pounds.

Meanwhile, the Flab Fighters weigh in before heading for the hills for a dog-walking session. Will they bank their calories or binge on a barrel of biscuits?

And in the home of size zero, Anna Richardson discovers where the overweight go to in LA. At a fat-fighting farm she goes for the burn with an extreme workout and meets the residents of Club Bounce, the dating disco for larger lovelies.

Swapping diets are 18-year-old superskinny Georgetta, who under-eats to look good but at a cost to her model looks. She will be paired with 28-stone supersizer Ameer, who is determined to lose weight so he can find a girlfriend.

Anna Richardson's Flab Fighters are four weeks into their battle of the bulge, and this epsiode embark on a calorie-burning rowing trip. But will they choose to have their cake and eat it?

There's also an update on the progress of four young women suffering from anorexia nervosa, where a shopping trip reveals the devastating physical affects of their body dysmorphia. Dietician Ursula Philpot then confronts the four young women's food anxieties by getting them to eat a highly calorific sandwich.

Pint-sized Tiffany Patterson had to grow up quickly when her mum left home, leaving her to become the breadwinner and meal-maker. Too busy to eat, the seven stone 25-year-old lives on a daily dose of energy drinks and little else.

Joining her for the five-day diet swap is DJ Keith Kelsey, whose out-of-hours eating has caused his weight to balloon to 30 stone. Dr Christian Jessen accompanies him to see 45-year-old Lisa Wheeler as she undergoes life-threatening weight-loss surgery.

It's ping pong in exchange for pizza as Anna Richardson takes on the Flab Fighters with a game of table tennis to show them how to have their favourite treats and still lose weight.

Plus four young women battling with anorexia nervosa face their food fears in the kitchen of a gourmet curry house, where they have to prepare and eat a highly calorific meal.

Two men confront their lifelong eating problems in the feeding clinic. A former jockey obsessed with keeping his weight down swaps diets with a man whose booze-binging is out of control.

In Los Angeles, Anna Richardson discovers that a fascination with celebrity mums lies behind the dangerous trend of extreme post-baby weight-loss regimes. She meets the Hollywood housewife who won't leave her Beverly Hills mansion until she's lost her pregnancy weight, and joins in an exercise class where babies are used as dumb-bells.

The Flab Fighters descend on Cardiff's Millennium Stadium for another lesson in how to enjoy their favourite treats and still lose weight. Will they be tempted by a tub of ice cream after a marathon session of step-running?

This week's show features Charlotte, whose dreams of being a pin-up model have fallen flat so far due to her desperate diet. She weighs just six stone and her childlike portions are doing nothing to help her gain the womanly curves she craves.

Joining her in the final five-day diet swap is 22-year-old Heather, who's passing on her terrible eating habits to her toddler daughter. The bride-to-be's reliance on ready meals is keeping her at over 20 stone - and no closer to getting into her perfect wedding dress.

Three weeks after two thirds of her stomach was cut away in life-threatening surgery, Lisa Wheeler reveals her dramatic weight loss.

Ditching diets in favour of a glamorous photo shoot, Anna Richardson discovers the Hollywood cheat's route to a slimmer body, including inch-reducing designer frocks and digital liposuction.

And the Flab Fighters' latest calorie-burner takes them to Silverstone for the dirty job of rally car washing in exchange for a celebratory glass of bubbly. While, at the end of their course of therapy, four anorexia sufferers describe their feelings as they visit a spa for a massage and face their biggest challenge of the course.

One year on, Dr Christian Jessen invites diet swappers back to discover how they're getting on with their new healthy lifestyles, and whether they've finally managed to banish their bad eating habits for good.

Twenty-six-year-old Kevin from Brighton weighed just 8 stone 5 lbs; he was living on coffee, cigarettes, pre-packed sandwiches and takeaways. He regularly skipped breakfast or lunch - or replaced them with chocolate or crisps.

We also catch up with Stefan, a 36-year-old milkman from Northern Ireland. A self-confessed 'carb junkie', Stefan weighed in at 37 stone and was keen to lose weight in a bid to get on the dating scene and boost his confidence.

So how are they both faring 12 months later?

Dr Christian Jessen checks up on diet swappers one year on.

Darryl from Derbyshire was a hefty 33 stone, and was keen to lose weight in a bid to be more active with his two young sons. The self-titled 'Blobbie Williams' lived on fry-ups, roast dinners, crisps and kebabs - often all in the same day. Darryl swapped with London mum Yasmin, whose diet was free of wheat, dairy, gluten, lactose and preservatives . Yasmin hoped to gain more curves and boost her energy.

London-based jazz singer Sandra was desperate to lose weight to combat her chance of developing diabetes, which runs in her family. She met seven-stone Tatiana in the food clinic. Tatiana, from Brighton, hated her skinny body, but couldn't bring herself to eat anything that wasn't lean and fat-free. How has the last year been for them?