Teens who falsely believe themselves to be overweight may be more likely to using diet pills or vomiting in an attempt to control their weight - behaviors linked with long-term weight gain.
The authors of the new study, from Florida State University College of Medicine in Tallahassee, were interested in what the health outcomes might be for teenagers of a healthy weight who misperceived themselves as being overweight.
To do this, the team examined data from the National Longitudinal Study of Adolescent Health (also known as Add Health) concerning the height, weight and self-perceptions of 6,523 adolescents.
At the start of the study, the adolescents rated what they thought their weight was, on a scale ranging from 1 ("very underweight") to 5 ("overweight"). The study participants had an average age of 16 at the start of the study and were followed-up when they were about 28 years old.
The results show that adolescents who had an inaccurate perception of themselves as being overweight had a 40% increased risk of obesity - defined as a body mass index (BMI) of 30 or more - in adulthood, compared with peers who had an accurate perception of their weight.
Although it might seem strange that healthy teens who feel that they are overweight subsequently actually become overweight, the authors suggest mechanisms that might drive this association between misperception and overall weight gain.
One theory proposed in the study is that teens who falsely believe themselves to be overweight may be more susceptible to using diet pills or vomiting in an attempt to control their weight - unhealthy behaviors that are known to be linked with weight gain over the long term.
The same psychological factors that drive the weight misperception could also cause the teens to have "lower self-regulatory abilities," the researchers suggest. And it is also likely that weight-related stigmatization could influence this group's weight-control behaviors, as previous studies have found that weight stigmatization is associated with obesity.
It is possible that these factors contribute to what the authors describe as a "self-fulfilling prophecy," where teens who see themselves as overweight then fail to take the required steps to maintain a healthy weight, "because as they gain weight, they physically become what they have long perceived themselves to be."
Boys who misperceive weight have 89% increased risk of adult obesity
A surprise finding of the research was a particularly strong association between misperceived weight and later obesity among males. The boys in the study who had a misperception of their weight had an 89% increased risk of adult obesity.
Study author Angelina Sutin says that it is not clear why the association is stronger for boys:
"It may be that girls are more attentive to their weight and may intervene earlier when they experience any weight gain. As such, the self-fulfilling prophecy may be stronger for boys than for girls. Physicians and other health care providers may also notice weight gain sooner for girls than for boys, or may be more likely to address any weight gain with girls than with boys. We were unable, however, to test exactly why there is this difference across the sexes."
Sutin says her study proves how complex the determinants of obesity are, suggesting that a greater understanding is needed of determinants at all levels, including psychological determinants, in order to address the obesity-related challenges faced by medical practitioners and policymakers.