Americans Less Healthy Than They Think: Study

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From beer to cronuts, Americans can't get enough if our national obesity problem is any indication. But a new study reveals many of us are in denial about our health—and are actually less healthy than we perceive.

In a study commissioned by Aetna, the insurance giant measured everything from how we rank our health compared with other generations—to why some of us exercise at all: To look good in our underwear.

"There is a disconnect," mused Keri Gans, about the study's participants. "It's surprising."

For example, while 67 percent of people believe they need to lose a median of 25 pounds, another 54 percent believe they can be healthy—even if they're overweight, the "What's Your Healthy" study found.

But jokes aside, misinformation can mean serious health consequences. More than a third of adults are classified as obese by the Centers for Disease Control.

"Being healthy is about being at a healthy body weight ... the higher their weight goes, the higher their risk increases," said Gans, also author of the "The Small Change Diet."

"There is that road to health. More people are getting on it," she said. "I just think we need more people to be on that road."

(Read More: American Medical Association Wants Obesity Treated as Disease)

The Greatest Generation

Many Americans firmly believe their own generation is the healthiest—even as most want to get cracking on losing an average of 25 pounds, according to the study.

Aetna's study also found that a lot of people—45 percent of those surveyed—think that their own generation is in the best shape, followed by their parents' generation and then by the generation younger than their own. "It's wishful thinking," said Gans,

And each generation thinks about being healthy in different way, according to the survey of 1,800 adults between the ages of 25 and 64.

Baby boomers—those 50 to 64—are twice as more likely than GenXers and millennials to describe themselves as healthy including getting regular doctor checkups or screenings.

Millennials—those between 18 and 34—are more likely than other generations to think that having good eating habits and exercising regularly equals being healthy—even as they are far more likely to hit the booze to deal with stress, which 37 percent of them admitted doing often.

And about half of the millennials and GenXers—those 18 to 48—said they snack on unhealthy food when they're stressed out. These two younger groups, perhaps not surprisingly, are more vain than the older baby boomers—with about a third of each of the younger generations saying they care about looking good in their underwear.

Just 19 percent of the baby boomers worry about how they look in their undies.

(Read More: Setting a Price on Weight Loss)

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Eternal Question: Sleep or Workout?

When it comes to exercise, 44 percent of those surveyed said they are more motivated to exercise when they can do it alone. That desire to exercise alone surprised Gans as group fitness classes including indoor cycling, boot camp and yoga are prevalent.

Regardless of who they exercise with, more people would rather sweat than sleep if they were granted an extra hour in their day, the study found. A total of 18 percent said they would exercise, compared with 13 percent who said they would snooze.

Gans said that was another example of peoples' disconnect, because "sleep is very important to your health."

"If you get enough sleep, you tend to lose weight," she said.

By CNBC's Dan Mangan. Follow him on Twitter @danpostman.