New research suggests that many obese and overweight teens do not realize that they are fat.
Researchers found that 40 percent of overweight or obese teenagers don't see themselves as being too heavy and think their weight is about right. This "lack of understanding" may be putting these teens at a greater risk of cancer and other disease, The Guardian reported.
Carrying excess weight increases the risk of up to 10 different types of cancer, including cancers of the breast and bowel.
"Overweight teenagers are more likely to become overweight adults at higher risk of cancer," Julie Sharp, head of health information at Cancer Research UK, said in a statement. "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. Making these changes as teenagers could help protect them from cancer as adults."
For the study, researchers collected and analyzed data from nearly 5,000 13 to 15 year olds. The teens were asked about their weight and if they thought they were too heavy, about right or too light. Researchers then checked their answers against their Body Mass Index (BMI) -- to see whether the reality matched the teenagers' perceptions of themselves.
They found that 73 percent of the teenagers had a BMI within the normal-weight range. Twenty percent had a BMI in the overweight category and 7 percent were categorized as obese. Of those in the obese and overweight category, around 40 percent thought they were about the right weight with 0.4 percent saying they were too light, The Telegraph reported.
The study also showed that 84 percent of the normal-weight teenagers correctly identified themselves as being about the right weight, The Guardian reported. A small number of normal-weight adolescents (7 percent) felt they were too heavy, and slightly more (10 percent) thought they were too light, with girls more likely than boys to think of themselves as being too heavy.
"This study was a cause for celebration and concern," Professor Jane Wardle, lead author of the study, said in a statement. "Young people who think they're overweight when they're not can sometimes develop devastating eating disorders, so we're delighted that most of the normal-weight teenagers had a realistic view of their body size."
Wardle said there needs to be effective ways of helping too-heavy teenagers slim down and maintain a healthier weight.
"It's vitally important that we find out whether it helps if they are more aware of their weight status. There are no easy answers," she added.
The findings are detailed in the International Journal of Obesity.
