As portion sizes and waistlines keep getting bigger, a recent study finds many adults are in denial about how much they weigh.

Sean Gallup, Getty Images

Sixty-nine percent of U.S. adults are either overweight or obese according to the Centers for Disease Control and Prevention. Despite the numbers, a recent Gallup poll found 55 percent of those surveyed don't think they are overweight, and only 18 percent  said they were trying to drop a few pounds.

Men were less likely than women to recognize that they were overweight, with 15 percent who said they were overweight versus 21 percent of women who said the same.

Deborah Carr, a sociology professor at Rutgers University, said there's a number of reasons overweight people might not consider themselves overweight.

"It could be that people are engaging in something called social comparison to convince themselves their body weight is fine - where you look around and you choose to compare yourself with those people who will make you feel good about yourself. So you might compare yourself with someone who is considerably heavier than you, and then as a result you will feel thin," Carr said.

Another factor, according to Carr, is what she called "vanity sizing."

"A shirt that's quite large might have been a size 12 a decade ago, and now it will be labeled a size 8, so women feel they're getting smaller because the clothing size has been changing."

Carr said another contributing factor could be the "fat and fit" phenomena, where overweight people who exercise are healthier than their thin counterparts that don't exercise.  Carr said those healthy overweight people don't think of themselves as overweight.

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