Can people really be obese and healthy at the same time? A recent study says people who have been dubbed "healthy obese" are still at a significant risk of health problems down the road.

New research suggest the health of supposedly "healthy obese" individuals tends to decline over time, calling question to the validity of this concept, the American College of Cardiology reported.

To make their findings researchers looked at the health of 2,500 men and women over a 20 year period. The participants were between the ages of 39 and 62; among the sample 181 were classified as obese, which included 66 who were classified as unhealthy obese.  Health obesity was defined as obesity with no metabolic risk factors.

"A core assumption of healthy obesity has been that it is stable over time, but we can now see that healthy obese adults tend to become unhealthy obese in the long-term, with about half making this transition over 20 years in our study," said lead study author Joshua Bell. "Healthy obese adults were also much more likely to become unhealthy obese than healthy or unhealthy non-obese adults, indicating that healthy obesity is a high risk state with serious implications for disease risk."

The researchers found after five years 32 percent of the participants who were initially classified as healthy obese had become unhealthy; after a decade 41 percent were unhealthy obese, 35 percent were unhealthy at 15 years, and over 51 were unhealthy obese after 20 years.

"Healthy obese adults show a greater risk for developing cardiovascular disease than healthy normal-weight adults, although this risk is not as great as for the unhealthy obese. Healthy obesity is only a state of relative health - it's just less unhealthy than the worst-case scenario. And as we now see, healthy obese adults tend to become unhealthy obese over time, providing further evidence against the idea that obesity can be healthy," Bell said.

The findings were published in a recent edition of the Journal of the American College of Cardiology.