An obese person isn't inevitably at increased risk of cardiovascular disease and death, a new U.K. study finds.
"The people really at risk are the ones who have obesity in combination with other metabolic health risk factors," said Mark Hamer, a principal research associate at University College London who worked on the study.
The results are in line with most previous research that defined metabolic health as having normal levels of markers like blood pressure, blood sugar, HDL, or "good" cholesterol, and C-reactive protein, which is a measure of inflammation in the body.
"People with good metabolic health are not at risk of future heart disease -- even if they are obese," Hamer told Reuters Health.
On the flip side, the non-obese in poor metabolic shape face as much risk as the unhealthy obese, the researchers concluded.
The findings, published in the Journal of Clinical Endocrinology & Metabolism, are based on more than 22,000 middle-aged participants in national health studies conducted in England and Scotland.
According to the researchers, the results suggest that metabolic factors may be more important in predicting a person's risk of cardiovascular disease than excess body weight in itself.
From a clinical perspective, stratifying individuals based upon their metabolic profile may help to identify those -- both obese and non-obese -- who should be treated with drugs or changes in diet and exercise, the study authors noted.
"We encourage obese people to lose weight for their health, but (some) provision should be made in how we screen people for metabolic risk," Hamer told Reuters Health.
An adult who has a body mass index -- a height-to-weight ratio -- of 30 or higher is considered obese. A normal BMI is between 18.5 and 24.9, and a BMI between 25 and 29.9 is considered overweight.
During the past 20 years, obesity has increased significantly in the United States. More than a third of American adults are obese, according to the Centers for Disease Control and Prevention.
Poor metabolic health?
For the new report, Hamer and a colleague collected data on participants' BMI and metabolic profiles and followed individuals, on average, for seven years. Then they looked at how many participants had died during the study period, and from what causes.
None of the participants had heart disease at the start of the study.
Almost a quarter were obese, and just under a quarter of those were considered "metabolically healthy obese" -- meaning they had no abnormal blood pressure, cholesterol, blood sugar or inflammation readings.
During the study period, more than 600 participants died from heart-related causes and 1,800 from other causes.
The obese individuals in good metabolic health were not at greater risk of dying from cardiovascular disease than the metabolically healthy non-obese, the researchers found.
But both non-obese and obese participants in poor metabolic health had a 59 percent and 64 percent increased risk of dying from heart disease, respectively, compared to the healthy non-obese.
Among the metabolically unhealthy participants, the non-obese had high levels of hypertension and inflammation -- comparable to those in the unhealthy obese group.
The metabolically unhealthy obese also had a 72 percent higher risk of dying from non-heart-related causes than those in good health.
That was after taking into account study participants' age, sex, smoking, physical activity and socioeconomic status.
Researchers found the results to be largely unchanged when they used waist circumference to define obesity instead of BMI.
'Think more broadly'
Hamer and his colleague note in their report that a strength of their study was having a large study population. But because the researchers only measured participants' metabolic risk factors at the beginning of the study, it's possible that some of the metabolically healthy obese went on to develop unhealthy readings.
The study shows the need "to think more broadly about obesity" rather than to focus on body weight alone, said Dr. Cora Lewis, a professor of preventive medicine and an epidemiologist at the University of Alabama, Birmingham, who was not involved in the research.
"If you are obese and you struggle with weight, but your (metabolic) risk factors are fine, that may not be such a bad place to be," Lewis told Reuters Health -- adding that only "a minority of people" fit the description of "metabolically-healthy obese."
Equally important, the study shows that people may be at increased metabolic risk no matter what they weigh, she noted.
Excess body fat may be carried not only under the skin, but also inside the abdomen, heart, liver and muscles -- making it hard to tell -- she added.
"BMI doesn't always tell you everything. If you are non-obese, but you have high cholesterol or hypertension, you have some work to do," Lewis said.