Normalisation of ‘plus-size’ body shapes lead to an increasing number of people underestimating their weight - undermining efforts to tackle the problem of obesity.

While attempts to reduce stigmatisation of larger body sizes - for example with the launch of plus-size clothing ranges - help promote body positivity, the study highlights an unintentional negative consequence that may prevent recognition of the health risks of being overweight.

The study by Raya Muttarak, from the University of East Anglia (UEA) in the UK and the International Institute for Applied Systems Analysis (IIASA) in Austria, examined the demographic and socioeconomic characteristics associated with underestimation of weight status to reveal social inequalities in patterns of weight misperception.

Analysis of data from almost 23,460 people who are overweight or obese revealed that weight misperception has increased in England.

Men and individuals with lower levels of education and income are more likely to underestimate their weight status and consequently less likely to try to lose weight.

Members of minority ethnic groups are also more likely to underestimate their weight than the white population, however they are more likely to try to lose weight. Overall, those underestimating their weight are 85 per cent less likely to try to lose weight compared with people who accurately identified their weight status.

The results, published in the journal Obesity, show that the number of overweight individuals who are misperceiving their weight has increased over time, from 48.4 to 57.9 per cent in men and 24.5 to 30.6 per cent in women between 1997 and 2015.

Similarly, among individuals classified as obese, the proportion of men misperceiving their weight in 2015 was almost double that of 1997 (12 vs 6.6 per cent).

“Seeing the huge potential of the fuller-sized fashion market, retailers may have contributed to the normalisation of being overweight and obese,” said Muttarak.

“While this type of body positive movement helps reduce stigmatisation of larger-sized bodies, it can potentially undermine the recognition of being overweight and its health consequences,” she said.

The study used data from the annual Health Survey for England, which contains a question on weight perception.

Focusing on respondents with a BMI of 25 or over, about two-thirds were classified as being overweight and one-third as obese. In order to assess trends in self-perception of weight status, the analysis was based on pooled data from five years - 1997, 1998, 2002, 2014, 2015 - of the survey.

The proportion underestimating their weight status was higher among overweight individuals compared with those with obesity (40.8 per cent vs 8.4 per cent).

Correspondingly, only about half of overweight individuals were trying to lose weight compared with more than two-thirds of people with obesity.