Americans may be much fatter than we all feared. The potential miscalculation seems to come down to an over-reliance on using the Body Mass Index (BMI), according to Dr. Eric Braverman and New York State Commissioner of Health Dr. Nirav Shah, who just published a study on the topic. "Based on BMI, about one-third of Americans are considered obese, but when other methods of measuring obesity are used, that number may be closer to 60 percent," Braverman says." Yikes!

To come to their conclusion, Braverman and Shah studied 1,400 men and women and compared their BMI to their actual body fat percentage (which they got from a dual-energy X-ray absorptiometry, or DEXA, scan). And, especially with women, they found depressing results. About half of the women who were not classified as obese by their BMI were declared obese by the DEXA scan. The percentage of men bumped up to obese by the scan was about 25 percent.

But the DEXA scan, which can tell bone from muscle from fat, produced even more interesting results than that! About a quarter of those studied who were obese according to their BMI were not obese according to the scan. All in all, about 39 percent of those studied whose BMI said they were overweight were actually obese when the docs took a closer look at their body fat.

Why does BMI seem to be a worse way to classify weight in women? Because women lose muscle and bone and replace it with fat faster than men. Braverman and Shah recognize that it isn't feasible for the average person to have a high-tech scan to tell them they are obese, but their study suggests ways that clinicians can modify BMI estimates to be more accurate. And those methods in turn would allow doctors to give better advice to their obese patients on how to better themselves. Or not! Being fat can be healthy, too.