People who rely on food banks risk developing nutritional problems because of the lack of fresh produce, an expert has warned.

Nearly a million people were helped by food banks in 2013-14, but the meals handed out are designed to be emergency relief. However, some users have been fed by the charities for up to 12 weeks.

Mel Wakeman, a Birmingham City University lecturer in health and nutrition, told The Guardian that she and her students had analysed the food that is usually given.

“We found that it’s very much processed food being donated, with little fresh produce. The meal plans we came up with revealed that in the long term there is a real risk of children and families becoming deficient in fibre, calcium, iron and a variety of vitamins,” she said.

“We’re not criticising what food banks are doing and, of course, only food that is safe to eat should be available, which limits the handling of perishable food.”

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Tinned soup, meat, puddings and pasta sauce were common types of food on offer.

“I would like to see more fresh produce in there. If levels of poverty continue to rise, then the level of support given to food banks may have to be increased so we don’t have a situation where families are prevented from accessing nutritious food,” Ms Wakeman said.

“Over longer periods, eating donated food that is often refined could result in nutritional deficiencies.”

The largest food bank charity, the Trussell Trust, tries to ensure food bank users do not become dependent on them and that supplies are only given for emergencies, not the long term. It aims to provide “nutritionally balanced” food but only some of its outlets offer fresh produce.