Call it the “Benefits Street effect” – the popularity of widely held preconceptions about unemployed people. And one of the most prevalent is that jobless people are more likely to be overweight than those in work.

While television documentaries and newspapers can help perpetuate this belief, academic studies also reinforce it. A series of studies have suggested that employers are biased against larger candidates when hiring staff. As a result, slimmer people tend to be employed first, leaving the overweight in the pool of the unemployed for longer.

But a study in the journal Preventive Medicine produces evidence that unemployed people are far more likely to be significantly underweight than the average person. The study’s authors, Dr Amanda Hughes and Professor Meena Kumari from the Institute for Social and Economic Research at the University of Essex, believe their findings provide a corrective to popular misconceptions about unemployed people and should alert health professionals to the heightened mortality risks that come from being underweight.

Hughes explained that she first became suspicious of a link between weight and unemployment when volunteering at a food bank. She observed that there were more people coming in who were painfully thin than were clearly overweight.

“There were people who had not eaten that day or the day before, or who had walked for two hours to get there, because paying for a return bus journey was out of the question,” she said. This set her thinking: had researchers become so concerned with obesity that they were ignoring the big picture?

“In public health there’s a really quite consistent and replicated finding that obesity is more common among more disadvantaged groups,” Hughes said. “It’s such a well replicated finding that, even in public health, there has always been this assumption that if unemployment affects body weight it will be in the direction of increasing it.”

But Hughes’s work suggests the picture is far more complex: that there is a “U-shaped” association between unemployment and body weight, with jobseekers tending to be more susceptible to being obese or underweight than those in work.

Using the Understanding Society database, a nationally representative survey of more than 40,000 UK households, Hughes looked at the BMI (body mass index) of 10,737 working-age adults between 2010 and 2012, a time when the effects of the recession were being keenly felt and substantial changes were being made to the benefits system.

Of those who were in employment, were full-time parents or in full-time education, 0.7% had a BMI below 18.5 and were therefore classed as underweight. But for those who were unemployed, the proportion shot up to almost 4%.

When factors such as education, gender and smoking were taken into account, it was revealed that the unemployed were still four times more likely to be classed as underweight than those who were not classed as unemployed.

Furthermore, just under 29% of those unemployed were classed as overweight compared with almost 40% of those in work or full-time education.

The study found that unemployed people were more likely to be obese, but only if they were non-smokers. Hughes suggested that this might be because some people on severely restricted budgets chose to prioritise their spending on tobacco rather than food.

“Together, these results point to a complex picture in which jobseekers, depending on the complexities of individual lives, are at increased risk of being either underweight or obese, each with their own associated health risks,” Hughes said.

“We now have quantitative evidence that many unemployed people are not eating enough in simple caloric terms. These results make an important contribution to research trying to explain the increased risk of chronic illness and mortality for unemployed people. They suggest that, at least in contemporary Britain, being underweight may contribute to this much more than previously realised.”