Pitsmoor Methodist Church in Sheffield offers senior citizens a weekly lunch service. This film follows the volunteers who keep the service going, and tells the story of what it means to the people who depend on it for their only hot meal. guardian.co.uk

Austerity Britain is experiencing a nutritional recession, with rising food prices and shrinking incomes driving up consumption of fatty foods, reducing the amount of fruit and vegetables we buy, and condeming people on the lowest incomes to an increasingly unhealthy diet.

Detailed data compiled for the Guardian, which analysed the grocery buying habits of thousands of UK citizens, shows that consumption of fat, sugar and saturates has soared since 2010, particularly among the poorest households, despite the overall volume of food bought remaining almost static. Food experts and campaigners called for government action to address concerns the UK faces a sustained nutritional crisis triggered by food poverty, which is in turn storing up public health problems that threaten to widen inequalities between rich and poor households.

The data show consumption of high-fat and processed foods such as instant noodles, coated chicken, meat balls, tinned pies, baked beans, pizza and fried food has grown among households with an income of less than £25,000 a year as hard-pressed consumers increasingly choose products perceived to be cheaper and more "filling".

Over the same period, fruit and vegetable consumption has dropped in all but the most well-off UK households, and most starkly among the poorest consumers, according to the data. It estimates the number of people who regularly achieve the "five-a-day" fruit and vegetable guideline has declined by 900,000 over the two years to May 2012.

The food campaigner Laura Sandys, who is Conservative MP for South Thanet in Kent, one of the UK's most deprived constituencies, said the findings demonstrated that the country faced a "major and growing" nutritional crisis. Sandys called for the government and the food industry to introduce measures to tackle food poverty, which she said would only intensify as food prices continued to rise and household incomes declined.

Sandys, who set up the Smarter Consumer Commission earlier this year to address food poverty, said: "We have to start to look at food as an important policy area and accept that many families are not going to be able to feed themselves in the way they have done, because of food price inflation, and lack of food skills."

Data for the Guardian's Breadline Britain investigation was collected by the consumer analyst Kantar Worldpanel, which operates a panel of 30,000 UK households across all income categories. The participating households electronically scan every grocery item they buy each week, enabling Kantar Worldpanel to build up a detailed, constantly updated picture of food purchasing habits.

Giles Quick, Kantar Worldpanel director, said: "We should worry about the child who goes to bed having not eaten a meal that evening but we should also worry about the much greater number of children who go to bed filled with food that is nutritionally poorThis problem affects many millions of homes on a regular basis. Left unchecked it is gradually creating a major social and public health problem."

Mary Creagh, shadow environment secretary, said the findings were "a big wake-up call" for ministers. "We need action to tackle what is an epidemic of nutritional poverty. We face a perfect storm of stagnant wages and high food prices at a time when the government is cutting huge holes in the social welfare net, and the impact will be felt most by the most vulnerable: children, women and the elderly."

The data, which captured consumer food buying habits up to June 2012, showed lower income groups were nutritionally most affected. The rising price of food – up 32% over the past five years according to official figures – meant the least well-off consumers focused their increasingly stretched food budgets on frozen and processed products at the expense of fresh fish, meat and fruit.

Food choices of poorer households were driven primarily by price and were more likely to be influenced by two-for-one style price promotions, most commonly associated with processed food products. Spending on chilled ready meals was up 25% in the past two years. "Feeding the family on a special offer pizza or ready meal represents a cheaper alternative to more complex, freshly cooked meals containing multiple ingredients," said Quick.

Fruit and vegetable consumption has fallen since 2010 across all households and almost all regions of the UK, but most markedly in the poorest households, and in north-west England. In Scotland, five-a-day intake has marginally increased since 2010, the data shows. This was attributed by Quick to the Scottish government's maintenance of a sustained social marketing campaign to encourage healthier choices.

Since May 2010, fruit and vegetable intake has decreased among consumers at all the leading supermarkets, excepting discounters such as Lidl and Netto, according to the data. Quick said price was the key factor: "Health is simply not seen as a priority when budgets are tight.

"Fruit and vegetables are much more likely to be consumed as a part of a home-cooked meal, and home cooking declines as working hours lengthen as families struggle to make ends meet and retain their jobs."

The findings echo official government statistics released last month, which showed the lowest income households started to buy less food in 2007, after the first of a series of food price rises. Over the past five years, the retail price of processed food has risen 36%, including a 15% rise in the year to 2012. Fruit prices have risen by 34% since 2007, and vegetables by 22%.

Liz Dowler, professor of food and social policy at the University of Warwick, said poor diet in early life stored up health problems for the future.

"Children who go hungry and who fill up on monotonous diets based on highly processed carbohydrates, little fresh vegetables and no fruit, are likely to have poor nutritional status – particularly insufficient micronutrients [vitamins and minerals] which are essential for building good immunity, enabling efficient metabolism and full body functioning."Professor Tim Benton of the Global Food Security programme, which brings together government departments and academic research councils, said the implications of rising food prices needed to be urgently addressed. "We have seen three food price spikes in five years. I can't see how that will go away – it can only get worse."

Sandys has set out a 10-point plan to address food poverty issues, including establishing a national food affordability index to monitor food prices and nutritional changes, mandatory food education in the early years schools curriculum, and a review of the effectiveness of the coalition's Change4Life healthy eating campaign.