Fat scanner may give better picture of health

Doctors have traditionally consulted BMI charts -- short for body mass index -- to determine whether a person is overweight or obese. But some experts say the charts don't give a complete, accurate picture of health.

"Your weight in pounds does not necessarily reflect how much fat you have, nor does it reflect where the fat is located," Dr. Steven Goldstein of NYU Langone Medical Center told CBS News.

Susan Reed certainly didn't think of herself as someone with a weight problem. She bikes and kayaks, and eats a mostly vegetarian diet.

"For BMI purposes, I fall right in the normal range," she said.

So imagine her surprise when her doctor told her she had a "fat" problem.

A potbelly or abdominal fat is much riskier than fat carried on the hips or buttocks. Goldstein authored a study that found that BMI charts mislead a lot of people.

"Twenty percent of the people with normal BMI, normal height and weight were greater than the 75th percentile for body fat," said Goldstein. "What we call 'the skinny fat.'"

The wakeup call for Susan Reed came when she had a modified version of a DEXA scan. It's similar to the scan that calculates your bone density and risk for osteoporosis, only this special version detects all of your lean and fat body mass, and, most importantly, where you carry that fat.

It turns out, Reed was what doctors call 'skinny fat.'

"I have to say I was shocked. I've had no other indicators that would lead me to think that it was a situation," she said.

This special body composition scan uses very low radiation, about the equivalent of what you're exposed to during a cross-country flight. The test costs $185 and is not covered by insurance. But some doctors like Goldstein say it's a much better way to assess your body-weight health risk than BMI charts.

It can also help identify so-called 'fat skinny' people, who are overweight according to BMI charts, but whose fat composition is normal and carried in safer body areas.