New research warns that the normalisation of 'plus-size' body shapes may be leading to an increasing number of people underestimating their weight -- undermining efforts to tackle England's ever-growing obesity problem.

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 Dr Raya Muttarak, from the University of East Anglia (UEA) 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% less likely to try to lose weight compared with people who accurately identified their weight status.

The results, published today 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% in men and 24.5% to 30.6% 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%).

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The study comes amid growing global concern about rising obesity rates and follows a 2017 report by the Organisation for Economic Co-operation and Development (OECD) that showed 63% of adults in the UK are overweight or obese.

Dr Muttarak, a senior lecturer in UEA's School of International Development, says her findings have important implications for public health policies.

"Seeing the huge potential of the fuller-sized fashion market, retailers may have contributed to the normalisation of being overweight and obese," said Dr 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. The increase in weight misperception in England is alarming and possibly a result of this normalisation.

"Likewise, the higher prevalence of being overweight and obesity among individuals with lower levels of education and income may contribute to visual normalisation, that is, more regular visual exposure to people with excess weight than their counterparts with higher socioeconomic status have.

"To achieve effective public health intervention programmes, it is therefore vital to prioritise inequalities in overweight- and obesity-related risks. Identifying those prone to misperceiving their weight can help in designing obesity-prevention strategies targeting the specific needs of different groups."

Dr Muttarak added: "The causes of socioeconomic inequalities in obesity are complex. Not only does access to health care services matter, but socioeconomic determinants related to living and working conditions and health literacy also substantially influence health and health behaviours.

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"Given the price of healthier foods such as fresh fruits and vegetables are higher than processed and energy-dense foods in this country, as a sociologist, I feel these inequalities should be addressed. The continuing problem of people underestimating their weight reflects unsuccessful interventions of health professionals in tackling the overweight and obesity issue."

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% vs 8.4%). Correspondingly, only about half of overweight individuals were trying to lose weight compared with more than two-thirds of people with obesity.