About 81% of overweight boys and 71% of overweight girls believe they are about the right weight, according to recent data released by the U.S. Centers for Disease Control and Prevention (CDC) from the National Health and Nutrition Examination Survey.

Overall, the survey, which collected data on the weight of U.S. adolescents between the ages of 8 and 15 from 2005 to 2012, found that about 30% of children and adolescents perceive their weight status incorrectly. That’s estimated to equate to about 9.1 million young people.

While the majority of overweight kids incorrectly classified their weight status, general weight misperception in the study also meant that kids who were not obese could think that they were, or that they could incorrectly consider themselves underweight.

The data also shows that weight misperceptions tended to be slightly higher among boys than girls, and had a higher prevalence among non-Hispanic black and Mexican-American kids. Weight misperception was significantly lower among kids and adolescents in higher-income families compared with kids in lower-income families.

Sadly, these are the same populations whose parents are more likely to be overweight, Dr. Daniel Neides, medical director for the Wellness Institute at the Cleveland Clinic, tells TIME. That suggests the possibility that overweight kids view their weight status as normal because that’s what they see in their own families. “As our country gets heavier, children don’t necessarily see it as abnormal,” he says. (Neides was not involved with the survey.)

The trouble is also that parents often don’t want to hear that their child is overweight. Prior research has shown that only about a quarter of parents of overweight kids say a doctor has told them that their kids were overweight. “People are very sensitive to weight and to growth charts, and [parents] will argue it hasn’t been updated in years,” says Neides. “We feel like young people are immortal and will be fine, and that population also doesn’t see the long-term implications.”

But overweight children is serious business. Kids are increasingly being diagnosed with diseases that usually only appear in adults, like Type 2 diabetes. A 2013 Harvard Medical School study also found a 27% increase in the proportion of children ages 8 to 17 with elevated blood pressure. “I am seeing people younger and younger coming into my office with osteoarthritis from weight,” says Neides. “We weren’t learning about kids with these problems when I was in medical school.”

The new data should serve as a warning to families and physicians that young people are confused about their weight status, and that if overweight kids continue to believe they’re the right weight, it could have detrimental effects on progress being made against the obesity epidemic.

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