Chicago ? You can look great in a swimsuit and still be a heart attack waiting to happen. And you can also be overweight and otherwise healthy.

A new study suggests that a surprising number of overweight people – about half – have normal blood pressure and cholesterol levels, while an equally startling number of trim people suffer from some of the ills associated with obesity.

The first national estimate of its kind bolsters the argument that you can be hefty but still healthy, or at least healthier than has been believed.

The results also show that stereotypes about body size can be misleading, and that even “less voluptuous” people can have risk factors commonly associated with obesity, said study author MaryFran Sowers, a University of Michigan obesity researcher.

“We’re really talking about taking a look with a very different lens” at weight and health risks, Sowers said.

In the study, about 51 percent of overweight adults, or roughly 36 million people nationwide, had mostly normal levels of blood pressure, cholesterol, blood fats called triglycerides and blood sugar.

Almost one-third of obese adults, or nearly 20 million people, also were in this healthy range, meaning that none or only one of those measures was abnormal.

Yet about a fourth of adults in the recommended-weight range had unhealthy levels of at least two of these measures. That means some 16 million of them are at risk for heart problems.

It’s no secret that thin people can develop heart-related problems and that fat people often do not. But that millions defy the stereotypes will come as a surprise to many people, Sowers said.

Study co-author Judith Wylie-Rosett emphasized that the study shouldn’t send the message “that we don’t need to worry about weight.” That’s because half of overweight people do face elevated risks for heart disease.

To arrive at the estimates, scientists analyzed nationally representative government surveys involving 5,440 people age 20 and over, and extrapolated to calculate nationwide figures.

The new study appeared in Monday’s Archives of Internal Medicine.