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Overweight Teens Often Underestimate Their Weight

Overweight Teens Often Underestimate Their Weight

Pam Harrison

July 17, 2015A significant proportion of overweight or obese adolescents in the United States and the United Kingdom think they are just about the right weight and are not concerned about their weight status, two new studies suggest.

“Adolescents with accurate self-perceptions of their body weight have greater readiness to make weight-related behavioral changes and are more effective in making the changes,” senior investigator of the US study, Jian Zhang, MD, DrPH, from the Jiann-Ping Hsu College of Public Health, Georgia Southern University, Statesboro, Georgia, said in a news release. “By contrast, overweight adolescents who do not perceive their weight status properly are less likely to desire weight loss, and are more likely to have a poor diet.”

Julie Sharp, PhD, head of health information at Cancer Research UK, concurs.

“Overweight teenagers are more likely to become overweight adults at higher risk of cancer,” she said in a news release. “So it’s important that young people who are too heavy have support to be more active and make healthy changes to their diet — being aware that they are above a healthy weight could be a first step.”

Boys Less Likely to Accurately Perceive Weight

In the US study, Hui Lu, PhD, from the Department of Social Medicine and Health Education, School of Public Health, Nanjing Medical University, China, and the Department of Social Medicine, School of Public Health, Fudan University, Shanghai, China, and colleagues used data from adolescents between the ages of 12 and 16 years who participated in the National Health and Nutrition Examination Survey (NHANES). They analyzed data from two survey periods, 1988 through 1994 (the “early” survey) and 2007 through 2012 (the “recent” survey) to compare the generational shift in adolescents’ perception of their body weight between the two intervals.

A total of 1720 adolescents completed the early NHANES survey, and 2518 completed the recent NHANES survey. Self-perceived weight status was assessed by face-to-face interviews, and body mass index (BMI) z-scores were calculated using directly measured weights and heights, using the 2000 Centers for Disease Control and Prevention Growth Charts as the reference.

“The percentages of self-perceived overweight [adolescents] declined between the two survey periods,” the authors report.

In the recent survey, 21% of overweight boys correctly perceived themselves to be overweight compared with 28% of boys in the earlier survey, whereas the percentage of obese boys who accurately perceived their weight status declined from 80% in the early survey to 58% in the recent survey (P < .05 for both comparisons).

The percentage of overweight girls who appropriately perceived themselves as overweight declined from 79% in the early survey to 36% in the recent survey (P < .05). The percentage of obese girls who accurately perceived their weight status declined from 89% in the early survey to 73% in the recent survey.

“Overall, girls’ self-perception was more accurate than boys’ in both early and recent surveys,” the investigators observe.

Compared with the early survey, the median BMI z-scores increased unevenly across demographic groups. The largest increase occurred among adolescents 12 years of age, and the smallest increase among those 16 years of age (both significant, at P < .05).

Across racial/ethnic strata, the declining tendency of accurately self-perceiving as being overweight among overweight/obese adolescents was more noticeable among white adolescents (probability ratio [PR], 0.64; 95% confidence interval [CI], 0.48 – 0.85) and least noticeable among black adolescents (PR, 0.76; 95% CI, 0.58 – 0.99).

Overall, after controlling for age, race/ethnicity, sex, and family income level, overweight/obese adolescents interviewed recently were 29% less likely to accurately self-perceive as being overweight (PR, 0.71; 95% CI, 0.62 – 0.82) compared with their counterparts with the same body weight who were interviewed earlier.

“The gap between the reality and perception about body weight status has been expanding among adolescents,” the researchers acknowledge.

They continue, “[t]he declining tendency may be indicative of a generational shift in body weight perceptions, presenting a vast challenge to obesity prevention among adolescents.”

The study was published online July 6 in the American Journal of Preventive Medicine.

Cancer Research UK

For the UK study, S. E. Jackson, PhD, from the Health Behaviour Research Centre, Department of Epidemiology and Public Health, University College London, United Kingdom, and colleagues analyzed data from the Health Survey for England from 2005 and 2012. The household survey is done annually.

Across all surveys, data from 4979 adolescents (2668 boys and 2311 girls) between the ages of 13 and 15 years were analyzed.

Weight status was deemed as normal or overweight/obese according to BMI standard deviation scores derived from objective measures of height and weight, using International Obesity Task Force standards.

“The majority of normal-weight adolescents (83% of boys, 84% of girls) correctly identified themselves as ‘about the right weight,’ ” Dr Jackson and colleagues report.

Overestimation of weight was uncommon among normal-weight teens, with only 4% of boys and 11% of girls identifying themselves as “too heavy.”

In contrast, only 53% of overweight/obese boys and 68% of overweight/obese girls correctly identified themselves as being “too heavy,” whereas 47% of boys and 32% of girls in the same weight category underestimated their weight, perceiving themselves to be either “about the right weight” or even “too light.”

In contrast to the US study, no trend in either overestimation or underestimation of body weight was observed among adolescents surveyed between 2005 and 2012.

“Previous studies have demonstrated strong associations between accurate weight perception and efforts to control weight in adolescents,” the UK authors write, “suggesting that those who fail to recognise their weight status may be at greater risk of continued weight gain and obesity-associated comorbidities in later life than those who recognise they are overweight.”

The study was published online July 9 in the International Journal of Obesity.

The authors have disclosed no relevant financial relationships.

Am J Prevent Med. Published online July 6, 2015. Full text

Int J Obesity. Published online July 9, 2015. Full text

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