Researchers who reviewed past studies found that even heavy people who didn't have high blood pressure or diabetes, for instance, had more heart attacks and strokes over time than healthy normal-weight people.
That runs contrary to the results of some recent shorter-term reports, which suggested people could be obese but heart-healthy.
"It made perfect sense to say there might be a group that have extra body fat but aren't necessarily at risk," James O. Hill said. "I think what this study says is, they are. It's just the risk may be lower (than among obese people who also have other problems) and it might take a little longer to see it."
Hill, executive director of the Anschutz Health and Wellness Center at the University of Colorado in Aurora, co-wrote a commentary published with the new analysis.
Canadian researchers pooled the results of eight studies that followed normal-weight, overweight and obese people over time.
Some of those participants were metabolically healthy. Others had a mix of heart-related risk factors like a large waist circumference, high blood pressure, high triglycerides, low "good" cholesterol and diabetes.
The studies included just over 61,000 people. Over a period of three to 30 years, depending on the study, about 4,000 of them died or developed heart problems.
At first, obese people without metabolic problems didn't seem to be any more at-risk than slimmer participants who were also metabolically healthy.
Then the researchers looked only at studies that followed people for 10 years or more. They found that over time, heavy but healthy people in those studies were 24 percent more likely to die, have a heart attack or stroke or develop heart failure.
"It was popular to say, well, maybe we shouldn't worry about these people," Dr. Bernard Zinman, who worked on the study, told Reuters Health.
"This kind of myth was propagated by looking at individuals and really not following the cohort for long enough."
Zinman is a senior investigator at the Lunenfeld-Tanenbaum Research Institute at Mount Sinai Hospital in Toronto and director of the hospital's Leadership Sinai Centre for Diabetes.
His team's findings are in line with recent research from Denmark. The authors of the Danish study found people's chances of developing heart problems went up as their weight went up, whether or not they also had metabolic problems (see Reuters Health story of November 12, 2013 here: reut.rs/17Sa7OP).
"The bottom line is that the stress of obesity on your cardiovascular system is always there," Zinman said. "It may be more in some people; it may be less in others."
NOT JUST ABOUT WEIGHT
Although extra weight was tied to long-term heart problems, normal-weight people could still have an elevated risk of death and heart disease, the researchers found.
They wrote in the Annals of Internal Medicine that people who had a combination of metabolic risk factors were more likely to develop heart problems, regardless of their weight.
Metabolically unhealthy normal-weight, overweight and obese people were all about three times more likely to get heart-related conditions or die of any cause than healthy normal-weight people.
"That's a little bit scary," Hill told Reuters Health.
He said it shows that although weight is important, it's not the only thing. And heavy people shouldn't be the only ones trying to improve their health to lower their chance of getting heart disease.
"Whether you're very obese or not obese, if you can engage in the behaviors that we know are part of a healthy lifestyle, you can probably reduce your risk as much as it's genetically possible to reduce it," Hill said.
Zinman recommended that people reduce their portion sizes while maintaining a healthy diet and exercise for half an hour at least five days per week.