Having tight abs, killer thighs and a “healthy” weight does not guarantee you immunity from having a stroke or a heart attack, suggests a new report from the University of Michigan. Researchers found that about half of overweight people have normal blood pressure and cholesterol levels, while an equally startling number of “fit” people suffer from a number of ills associated with obesity. The bottom line? Size can be misleading as a measurement of true health.

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. And almost one-third of obese adults, nearly 20 million people, were in this healthy range as well.

The study validates the argument that the medical community should assess what is overweight or obese by using a standard other than Body Mass Index (BMI), which does not differentiate between fat and lean tissue. Some experts want to look at waist size instead as a measure of what is fit and what is not.