Teens Are Increasingly Underestimating Their Weight

By many measures, teen obesity is an international public health crisis, with data showing that 340 million adolescents worldwide are affected, a number that’s risen tenfold in the last half century. The largest study to date of how teenagers perceive their own weight—encompassing 40 countries and 16 years—suggests that the same teens are increasingly underestimating how much they weigh.

According to Anouk Geraets, a postdoctoral researcher at the University of Luxembourg and the study’s lead author, the findings, published July 5 in the journal Child and Adolescent Obesity, help explain why so many countries’ attempts to course correct the rise of teenage obesity “don’t have the right effect that they want to have.” Geraets argues that the data suggest health care experts may be overlooking the importance of discussing body perceptions in conversations with adolescents about their health and habits—and highlight why we need to reconsider how weight and health are measured.

Gareats’ team used World Health Organization data from longitudinal international school-based surveys, including 746,121 teens worldwide who had answered questions about weight perception between 2002 and 2018. “What’s very important is that the study has asked the same questions across the years,” says Geraets, allowing findings from each survey year to be compared directly.

Across all years and countries, teens underestimated their weight by about 13%. And that number is growing, with the global annual average of teen weight underestimation growing by some 33% between 2002 and 2018. On the other hand, the increase in underestimation was accompanied by a decrease in overestimation, mostly accounted for by changes in how girls reported experiencing their weight. Geraets believes both trends could be attributed to changing body ideals throughout the years included in the study. “In the ‘90s, there was this skinny body ideal, and we started in 2002,” when those standards were still fairly prevalent, she says. Teens in the 2010s “were maybe not comparing themselves to skinny models like [they were] the ‘00s.”

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Additionally, about 60% of teens were correct in their own assessment of their weight, a measurement that increased or remained consistent over time in all but 8 of the 41 included countries—a trend also driven largely by girls.

Geography seemed to play less of a role. Geraets’ team found that, although teens in countries with higher obesity rates were generally more likely to misjudge their weight, when teen obesity rates in a given country went up, it didn’t necessarily correlate to changes in overestimation or underestimation far outside the country’s average rates. It’s possible, then, that the changing ways teens view their bodies could be the result of global cultural changes. Increased smartphone ownership worldwide, for instance, means that teens on every continent are now able to spend time in the same corners of the internet.

In the U.S. especially, where teens have to process messages about diet culture and body size from all sides, understanding where weight perception can play a more helpful role would likely mean doing more research that uses Geraets’ findings as a jumping-off point. As obesity rates have grown, so too has the number of teens affected by eating disorders, which pose serious health risks at any weight. A recent study of more than 5,000 teenagers with obesity across 10 countries found that caregivers and doctors were often unaware of self-managed attempts at weight loss. This type of miscommunication can strip teens of the opportunity to receive appropriately tailored health care and leave them open to messages about obesity that over- or under-stress the implications it has for their long-term health.

Messaging focused on obesity alone can also deny teens a nuanced picture of their health beyond Body Mass Index (BMI), which remains both the metric used to determine weight status and a standard in research. And though it can be useful when processing large datasets, there’s a large margin of error when using BMI as an indicator of anything on an individual level. Geraets herself prefers waist circumference over BMI, which her study was limited too, as a predictor of cardiovascular health. “If you really want to have the best measures,” she says, “you should look much further than BMI.” For these reasons and more, teenagers should never be left to deal with their weight and body image on their own, suggests Geraets. “If you want to lose weight, if you want to gain weight, I think it’s important to do this in a responsible manner and contact a doctor,” she says.