"Being thin doesn't automatically mean you're not fat," said Dr. Jimmy Bell, a professor of molecular imaging at Imperial College, London.

Since 1994, Bell and his team have scanned nearly 800 people with MRI machines to create "fat maps" showing where people store fat. The data show that people who maintain their weight through diet rather than exercise are likely to have major deposits of internal fat, even if they are otherwise slim.

"The whole concept of being fat needs to be redefined," said Bell, whose research is funded by Britain's Medical Research Council. Doctors worry that thin people, lacking a clear warning signal, such as a rounder middle, may be lulled into assuming falsely that because they're not overweight, they're healthy. "Just because someone is lean doesn't make them immune to diabetes or other risk factors for heart disease," said Dr. Louis Teichholz, chief of cardiology at Hackensack University Medical Center in New Jersey, who was not involved in Bell's research.
Even people with normal body mass index scores, a standard obesity measure, can have surprising levels of fat deposits inside. Of the women Bell and his colleagues scanned, as many as 45 percent of those with normal BMI scores (20 to 25) actually had excessive levels of internal fat. Among men, the percentage was nearly 60 percent.

Relating the news to what Bell calls TOFIs -- people who are "thin outside, fat inside" -- is rarely uneventful. "The thinner people are, the bigger the surprise," he said, adding the researchers even found TOFIs among people who are professional models.

According to Bell, people who are fat on the inside are essentially on the threshold of being obese. They eat too many fatty, sugary foods, and exercise too little to work it off, but they are not eating enough to actually be fat.

Scientists believe we naturally accumulate fat around the belly first, but at some point, the body may start storing it elsewhere. Still, most experts think that being of normal weight is an indicator of good health, and that BMI is a reliable measurement.

"BMI won't give you the exact indication of where fat is, but it's a useful clinical tool," said Dr. Toni Steer, a nutritionist at Britain's Medical Research Council.

Doctors are unsure about the exact dangers of internal fat, but some suspect it contributes to the risk of heart disease and diabetes. They theorize that internal fat disrupts the body's communication systems. The fat enveloping internal organs might be sending the body mistaken chemical signals to store fat inside organs such as the liver or pancreas. This could lead to insulin resistance, type 2 diabetes or heart disease.

The good news is that internal fat can be easily burned off through exercise or even by improving your diet.  "Even if you don't see it on your bathroom scale, caloric restriction and physical exercise have an aggressive effect on visceral fat," said Dr. Bob Ross, an obesity expert at Queen's University in Canada.

================================

Start your own walking program  
New StepTracker Available at special prices.  See the results of the Step Program Study.  
http://www.diabetesincontrol.com/programs/steps/index.shtml
Purchase your own pedometers and receive the Steps to Health Program at no charge. http://www.rx4betterhealth.com/steptracker/
The Only Pedometer on the Market That Comes With a Program for Success!

================================

FACT: