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Inaccurate idea of own body weight may be strong factor in unhealthy dieting

Overestimating one’s own body weight and a desire to change it are the factors most strongly associated with unhealthy eating behaviours such as fasting, using diet pills, vomiting and using laxatives, according to a study published in the open access journal BMC Public Health.

Researchers at Imperial College London found that unhealthy dieting behaviours were more common among adolescent females than males in the US, with 26.2% of females performing an unhealthy dieting behaviour in 1999 and 22.7% in 2013, compared to 10.4% of men in 1999 and 10.1% in 2013.

Dr Filippidis, the corresponding author said: “These findings are important as unhealthy dieting behaviours are linked to serious health consequences, such as becoming dangerously underweight, and are ineffective for long-term weight loss for people who are overweight. In light of the increasing levels of weight mismanagement among youths, this is a pressing issue.  Public health policies should look to helping adolescents improve the accuracy of their weight status perception to help reduce unhealthy dieting behaviours in future.”

The authors also found that females were more likely to overestimate their weight and males were more likely to underestimate their weight, which has previously been associated with being less likely to lose weight. The proportion of both males and females overestimating their weight dropped; from 21.9% in 1999 to 15.9% in 2013 for females and 6.9% in 1999 and 6.1% in 2013 for males. Underestimation of weight status increased among females, from 21.2% in 1999 and 25.0% in 2013, and also in males from 30.6% in 1999 and 40.2% in 2013.

Ms Sarah Chin, first author of the study, said: “High levels of weight misperception increases the likelihood of clinically inappropriate weight change intentions, which was found to be associated to unhealthy dieting behaviours in this study.” 

The researchers observed significant racial disparities in unhealthy dieting behaviours, with non-white groups displaying higher levels of fasting and purging which have previously been reported as important precursors of anorexia nervosa and bulimia nervosa respectively. As racial disparities have persisted over time, the authors suggest that this may disadvantage minority groups long-term.

The researchers used data from 113,542 adolescents, collected between 1999 and 2013 in the Youth Risk Behavioural Surveillance System, which monitors the health risk behaviors among 9th through 12th grade students in the US. As part of the survey, adolescents answered questions about their weight perception, weight change intentions and dieting behaviors. The authors looked at the relationship between these factors and unhealthy dietary behaviours. They defined unhealthy dietary behaviours as fasting for more than 24 hours, taking diet pills, powders or liquids and purging behaviours such as vomiting or taking laxatives.

The authors caution that the study’s use of self-reported survey data may have introduced information and recall bias. The cross-sectional nature of this study does not allow for conclusions about cause and effect between perceptions of weight, intentions to change weight and unhealthy dieting behaviors.



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Notes to editor:

1.    Research article: 
Trends and correlates of unhealthy dieting behaviours among adolescents in the United States, 1999–2013
Chin et al. BMC Public Health 2018
DOI: 10.1186/s12889-018-5348-2

When the embargo lifts the article will be available at:

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