TORONTO -- The notion that someone can be obese yet still healthy is a myth, say researchers, who found that obesity carries a higher risk of premature death compared to that of normal-weight people, regardless of cholesterol, blood pressure and blood-sugar readings.

In an analysis of data pooled from several previous studies, researchers at Toronto's Mount Sinai Hospital found people who were obese but metabolically healthy had a significantly increased risk of having a heart attack or stroke and of dying prematurely.

"Our research findings challenge the myth that there is such a thing as healthy obesity if people maintain normal-range readings of cholesterol, blood glucose and blood pressure," said endocrinologist Dr. Ravi Retnakaran, co-author of the study in this week's Annals of Internal Medicine.

Researchers reviewed eight studies from the last decade, which included a total of more than 61,000 participants who were followed for a mean period of 11 years. Almost 4,000 of the subjects had cardiovascular events such as a heart attack of stroke.

The studies evaluated subjects' metabolic status, including cholesterol levels, blood-sugar levels and blood pressure. Measurements also included waist circumference, as excess abdominal fat tissue can contribute to the development of Type 2 diabetes, for example.

The studies compared fatal and non-fatal cardiovascular events, as well as other causes of death like cancer, across three weight categories -- normal, overweight and obese.

Researchers said the comparative risks for premature death in the three weight groups became especially apparent after 10 years of followup.

Lead author Dr. Catherine Kramer said that even in the absence of such markers as high blood pressure or elevated cholesterol, an obese person with a body mass index, or BMI, of 30 or greater had a 24 per cent higher risk of having a heart attack or stroke or of early death compared to a normal-weight person.

"So we are telling people and doctors that it is not OK to be obese, even though you don't have metabolic abnormalities," Kramer said in an interview Monday. "This excess of weight still confers increased risk for cardiovascular events."

For study participants who were overweight, with a body mass index of less than 30 but greater than 25, the risk of cardiovascular events was the same as for normal-weight subjects during the study periods.

"But we also evaluated all metabolic parameters -- lipids, blood sugar, blood pressure -- and we show that people with metabolically healthy overweight already have increases (in levels) compared to normal weight," said Kramer.

While those readings weren't yet in the so-called unhealthy zone, "this is a sign for us. Maybe they are still healthy now, but in five, 10 years, maybe (the excess weight) will have an effect on metabolic health."

In an accompanying editorial, Drs. James Hill and Holly Wyatt of the University of Colorado say the Toronto researchers provide strong evidence that "healthy obesity" is a myth.

"The review casts doubt that any obese persons have no long-term risk for cardiometabolic disease," they write. "Obesity affects almost all aspects of human function and physiology.

"Obesity also increases risk for Type 2 diabetes, kidney disease and some types of cancer. It is linked to orthopedic problems, reproductive problems, depression, asthma, sleep apnea, renal disease, back pain, skin infections and cognitive decline. Obesity produces social stigma and overall reduced quality of life.

"It would be a mistake to label obese persons as healthy on the basis of only the presence or absence of risk factors for cardiometabolic disease."

Kramer said that regardless of lab tests that point to a healthy metabolic profile, doctors need to stress to overweight and obese patients that they are potentially shortening their lives and strongly encourage them to shed excess pounds through diet and exercise.

"Our message to physicians is that for obese individuals, normal metabolic status regarding blood pressure, cholesterol and blood glucose is not protective. If they can start to lose weight, that's a benefit."

In 2011, about 18 per cent of Canadian adults were classified as obese.