The Duchess of York will swap her penthouse in Manhattan for a £40-a-night guesthouse on a deprived council estate in Hull when she investigates obesity for an ITV reality show.

ITV hopes that she will be a hit with viewers after it suffered a string of ratings flops. It chose to trumpet its new signing on the day that it announced a 35 per cent fall in annual profits and a drop in audience share.

In the reality show the duchess, who is 48, will follow a family of seven as they struggle with their waistlines on the Preston Road Estate in East Hull. She will stay at the East Thorpe Guest House, which is popular with dockers and lorry drivers.

She promised to use her experience of “eating disorders, low self-esteem, family conflict, financial crisis, divorce and bereavement” to help familes on the estate to improve their lifestyle. The results will be screened this summer in The Duchess in Hull, a two-part ITV special.

Families in Preston Road have some of the lowest incomes in Britain, as well as high levels of teenage pregnancy, crime and unemployment. The estate has been selected for a £55 million regeneration scheme.

The duchess said: “I do like being with people at street level, where I feel they accept me as I am.”

At the guesthouse she was offered a twin room with television, coffee-making facilities and an en suite bathroom. On her first day she was taken on a shopping expedition with fellow single mothers to Netto, a low-budget supermarket. The duchess picked out cream crackers and margarine.

Household debt is a big problem on the estate and the duchess will employ her experience of paying off about £4 million to Coutts, the Royal Family’s bank, to offer advice.

The ambassador for Weight Watchers was assigned as a mentor to Tonia and Mick Sargerson, who have four children living at home. She replaced their diet of crisps with fruit and vegetables and advised them on an exercise regime. Jean-Christophe Novelli, a Michelin-starred chef, produced a diet plan.

Mrs Sargerson, 40, said: “The duchess was very down to earth. I lost a stone the first week they were filming. I have bought more fruit. Mick, bless him, hasn’t lost a pound.”

The duchess, who has a burgeoning television career in the US, said: “The family I met in Hull live in a way that I hadn’t experienced – feeding six on a week’s benefits.”

Some of the residents from the Preston Road Estate were sceptical that the duchess could transform their lives. Jolene Brady, a mother of four who lives off £169 a week in benefits, has debts of £35,000. “If Fergie had come in my house she wouldn’t have wanted to come back again,” she said.

The duchess, who lives in a £2.5 million apartment overlooking Central Park, will return to Hull today to lecture young people on obesity.

ITV is expected to sell the programme to international broadcasters. This week Monarchy: The Royal Family at Work, attracted 14 million American viewers on ABC.

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