Do People Know When They’re Overweight?

A new study finds that most people can estimate their height-weight combinations fairly accurately. However, overweight and obese people miss the mark when they’re asked to characterize the healthiness of their weight-to-height status.

Indeed, among adults who met the National Institutes of Health criteria for being obese, only 15 percent realized they were obese, notes Kimberly P. Truesdale of the University of North Carolina. She says that her team’s findings, which she reported in San Francisco earlier this month at the Experimental Biology ’06 meeting, have important public health implications: “If [obese] people don’t identify with being obese, then they’re most likely going to ignore messages warning of health risks.”

The important thing now, she says, is to verify how universal these trends are. If they’re confirmed, she says, the question then becomes, What factors contribute to misperceptions about weight among people who most need to slim down.

The breakdown

Truesdale and June Stevens, also from the University of North Carolina, recruited 104 white and black men and women between the ages of 45 and 64. The volunteers first answered questions about their heights and weights and then underwent measurements by the researchers.

The measurements placed roughly one-third of the group into each of the categories normal weight, overweight, and obese.

The researchers calculated each volunteer’s estimated and actual body-mass index, or BMI, a measure of health that accounts for both height and weight.

Based on federal guidelines, people with BMIs less than 18.5 are considered underweight, and those who fall in the range 18.5 to 24.9 are considered normal weight. BMI’s from 25 to 29.9 indicate a person is overweight, and BMIs 30 and above define obesity.

Truesdale and Stevens found that their subjects’ self-reported and actual vital statistics yielded almost identical BMI’s. However, when asked to characterize their weight status—from underweight to obese—only about 70 percent of normal weight and overweight people did so accurately. When they erred, normal-weight individuals tended to think they were overweight. By contrast, overweight people who misjudged their status were most likely to round down, describing themselves as of normal weight.

The real disconnect occurred among obese volunteers. As noted earlier, 85 percent misjudged their BMIs, estimating the figures to be lower than they actually were.

To further probe perceptions on weight, Truesdale and Stevens asked each participant to estimate how many pounds he or she would have to gain or lose to fall into each respective weight category, from underweight to obese. How far off the mark an individual’s estimates were tended to rise with his or her actual weight.

Consider the hypothetical 5’4″ woman and 5’10” man. To be normal weight, based on federal guidelines, she should weigh between 108 and 145 pounds and he between 129 and 174 pounds. Normal-weight participants in the study came closest, on average, to estimating how many pounds they’d need to lose or gain to hit the center of their height-appropriate weight ranges. Obese individuals, however, typically underestimated how much they had to lose to get to such a point in a normal-BMI range.

When it came to estimating what their weights would be if they were obese, only normal-weight volunteers hit the mark: height-adjusted values equivalent to 174 or more pounds for a 5’4″ woman and at least 208 pounds for a 5’10” man. Obese volunteers, in contrast, didn’t come close. They estimated values that, for instance, would have put the minimum threshold for obesity in a 5’4″ woman at 222 pounds and for a 5’10” man at 241 pounds.

Such findings may offer one explanation for the escalating global obesity epidemic, Truesdale told Science News Online. People who most need to cut their weight may not realize they’re in that category, she says. Indeed, she suspects that as average waistlines grow, heavy people see themselves as having normal and presumably healthy weights.

Studies have relentlessly pointed to problems associated with excess weight, including elevated risks of cancer, heart disease, diabetes, arthritis, and more. With unhealthy weight gains beginning in the elementary school set (see Honey, Let’s Shrink the Kids), Truesdale says that public health professionals may have to target messages to children and let them know that other kids’ weights aren’t necessarily healthful.

You can figure your BMI by plugging your height and weight into a calculator on the National Heart, Lung, and Blood Institute’s Web site, referenced below.

Janet Raloff

Janet Raloff is the editor of Science News for Students, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer.

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