A new study claims that the notion of healthy obesity is a myth, as most obese people over time suffer from poor health and chronic illnesses.  The "obesity paradox" is a theory that argues that obesity might improve some people's chances of surviving an illness, such as heart failure, says lead researcher of the study Joshua Bell, a doctoral student in the University College London's department of epidemiology and public health.

Research tracking the health of more than 2,500 British men and women for two decades found that half the people initially considered "healthy obese" ended up suffering from poor health as the years passed.

"Healthy obesity is something that's a phase rather than something that's enduring over time," Bell says. "It's important to have a long-term view of healthy obesity, and to bear in mind the long-term tendencies. As long as obesity persists, health tends to decline. It does seem to be a high-risk state."

The idea of "healthy obese" originated from a study of people who were overweight that did not suffer typical obesity-related health problems such as high blood pressure, cholesterol and elevated blood sugar, according to Dr. Andrew Freeman, director of clinical cardiology for National Jewish Health in Denver.

"No one can say how the obesity paradox works, but some have speculated that people with extra weight might have extra energy stores they can draw upon if they become acutely ill," Freeman says.

To test this theory, researchers measured the body mass index, cholesterol, blood pressure, fasting blood sugar and insulin resistance, and ranked them as either healthy or unhealthy and obese or non-obese.  At the beginning of the study, about one-third of the obese people had no risk factors for chronic disease and were ranked as healthy obese.  Over time, however, this group began to develop risk factors for chronic disease and by the end of the study 51 percent of the group had fallen into the unhealthy category.

"The longer one is obese, the more likely they are to induce damage," Freeman says. "I have very seldom seen people who are obese for the long-term not have a condition that requires treatment."

And Bell believes his findings demonstrate that people who are obese should try to lose weight, even if they don't currently have any risk factors for chronic illnesses related to weight. 

"All types of obesity warrant treatment, even those which appear to be healthy, because they carry a high risk of future decline."