Weight misperceptions strongly associated with unhealthy dieting

Research published today in BMC Public Health, which analyzed data from 113,542 US adolescents, finds that overestimating one’s own body weight and a desire to change are factors most strongly associated with unhealthy dieting behaviors like fasting, purging and using diet pills.

It is no secret that the United States (US) is facing an obesity problem; adolescent obesity is currently three times more prevalent than it was in the 1980s. What is perhaps surprising is that at the same time, the prevalence of US households with both overweight and underweight members exceed 5% of the population. This highlights the US’s dual burden of weight mismanagement at both ends of the weight spectrum. Moreover, it is striking to note that this trend is accompanied by a high persistence of unhealthy dieting behaviors among youths.

Unhealthy dieting behaviors such as fasting for extended periods of time or purging via forced vomiting have been shown to be risk factors of several eating disorders (EDs). Unhealthy dieting is not the same as EDs since EDs are classically linked with psychological implications, but they may act as precursors to more severe mental disorders and can lead to being dangerously underweight.

Unhealthy dieting behaviors have also been shown to be ineffective for long-term weight loss for people who are overweight, and could cause weight gain in that population since they are associated with counter-productive practices such as reduced physical activities and a decrease in fruit and vegetable consumption. As seen, these behaviors could potentially exacerbate the weight mismanagement issue in both directions.

Perceiving one’s weight

Although numerous public health strategies to combat weight mismanagement have been implemented over the years, many have focused on behavioral interventions such as diet and exercise education. In our research, we wanted to explore in detail the role of one’s perception of their own weight and so examined associations between self-perceptions of weight status, weight change intentions, and unhealthy dieting behaviors across the different sex, age, race and weight spectrum in US adolescents.

To find out, we analyzed data from 113,542 adolescents collected between 1999 and 2013 in the Youth Risk Behaviour Surveillance System, which monitors the health risk behaviors among 9th through 12th grade students in the US through school-based surveys. The survey included questions on self-perception of weight, weight change intentions and unhealthy dieting behaviors. Measures of self-reported unhealthy dieting behaviors were fasting for 24 hours or more, taking diet pills/powders/liquids, and vomiting/taking laxatives, in the last 30 days in order to lose weight or keep from gaining weight.

We discovered that overestimating one’s own body weight and a desire to change it were most strongly associated with unhealthy dieting.

We found that adolescent girls were more likely to overestimate their weight, while boys were more likely to underestimate. Also, unhealthy dieting was more common among girls than boys, with 26.2% of girls performing an unhealthy dieting behavior in 1999 and 22.7% in 2013. These figures for boys were 10.4% in 1999 and 10.1% in 2013. After adjusting for sex, age and race, we discovered that overestimating one’s own body weight and a desire to change it were most strongly associated with unhealthy dieting.

We also observed significant racial disparities in unhealthy dieting behaviors, with non-white groups displaying higher levels of fasting and purging, which are important precursors of anorexia nervosa and bulimia nervosa respectively. As racial disparities were found to have persisted over time, it could mean that minority groups may be disadvantaged in the long term.

These findings are important as unhealthy dieting behaviors are linked to serious health consequences and can further worsen the weight mismanagement observed in US adolescents. This study suggests that high levels of weight misperceptions, particularly overestimation, increase the likelihood of clinically inappropriate weight change intentions, which was found to be associated to unhealthy dieting behaviors. Hence, public health policies should look to helping adolescents have an accurate perception of their own weight to help reduce unhealthy dieting in the future.

As ever, there are caveats: as this study used self-reported survey data, information and recall bias may be a factor. Moreover, as we were unable to track the same individuals over time, causation between the factors could not be drawn conclusively. Nevertheless, the persistence of the high prevalence of unhealthy dieting behaviors, especially among females across all racial groups, is concerning. Further research into weight status perceptions may inform efforts to curb this worrying trend.

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