Rosie Turner from Cambridgeshire has just turned 30 and is preparing for her wedding to fiancé Randy in three months time. Like every bride-to-be, Rosie wants to look and feel her best on her big day, but at nearly 16 stone, she's worried she won't fit into her dress.

Rosie is a rep for a travel company and spends most of her working week on the road. During the day, she grabs fast food from service stations and pizzerias because it's 'quick and easy', and she blames this lifestyle for piling on the pounds. She often feels too exhausted to cook in the evenings, so her dinner consists of an additive-laden takeaway or microwave meal. On top of this, she constantly indulges her sweet tooth with cakes, pastries and chocolate bars, and never takes any exercise.

Enter holistic nutritionist Gillian McKeith, who starts by reviewing Rosie's food diary and confronting her with a week's worth of her consumption laid out on a table. Worryingly, the selection includes no fresh food; no vegetables apart from a few over-cooked peas and only a single piece of fruit! Gillian is concerned that Rosie is unaware of the impact of such a diet on her long-term health, and explains how the excess sugar could eventually lead to Type 2 diabetes. To illustrate her point, Gillian produces 550 meringues - the staggering equivalent of Rosie's monthly sugar intake!

Rosie is often constipated, lacks energy and has a low sex drive; all symptoms that Gillian believes can be countered or improved by her diet. A stool analysis and blood tests confirm to Gillian that Rosie has poor digestion and low iron store levels, so after consulting a medical doctor, Gillian sets about designing a bespoke 8-week detox plan to address Rosie's specific needs and help her get into her wedding dress.

Processed foods, dairy products and refined sugar are all banished: in their place are lots of beets and green leafy vegetables to increase Rosie's iron store levels; plenty of fibre to restore her bowel function; and zinc-rich foods like strawberries to stimulate her sex drive. Gillian even takes Rosie to a service station to show her some healthy alternatives to a sausage sandwich!

But will this be enough to persuade Rosie to ditch the convenience food and change the eating habits of a lifetime?

Two months on, and Gillian returns to find that Rosie is nearly two stone lighter and bursting with energy. She is no longer constipated, feels much fitter and has a new-found confidence in her appearance. Although she admits to struggling with the preparation involved, she plans to stick to her new eating plan in the run-up to her marriage and beyond.

As a parting shot, we see footage of a radiant and much slimmer Rosie in her wedding dress, as she marries Randy in Barbados.