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.