So you thought you could afford not to exercise if you were thin. Think again, for "being thin doesn't automatically mean you're not fat", says Jimmy Bell, a professor of molecular imaging at the Imperial College of London.

If it really is what's on the inside that counts, then a lot of thin people might be in trouble. Some doctors, like Bell, now think that the internal fat surrounding vital organs such as the heart, liver and pancreas - invisible to the naked eye - could be as dangerous as the more obvious external fat that bulges underneath the skin.

Since 1994, Bell and his team have scanned nearly 800 people with MRI (magnetic resonance imaging) machines to create "fat maps" showing where people store fat.

The data they've collected show 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," says Bell, whose research is funded by Britain's Medical Research Council.

Without a clear warning signal doctors worry that thin people could be lulled into falsely assuming that they're healthy because they are not overweight.

"Just because someone is lean doesn't make him immune to diabetes or other risk factors for heart disease," says chief of cardiology at Hackensack Hospital in New Jersey, Louis Teichholz, even though he was not involved in Bell's research.

Even people with normal body mass index (BMI) scores - a standard obesity measure that divides your weight by the square of your height - can have surprising levels of fat deposits inside.

According to Bell, people who are fat 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.

Experts have long known that fat, active people can be healthier than their skinny, inactive counterparts.

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," says Bob Ross, an obesity expert at Queen's University in Canada.

Agencies

(China Daily 05/12/2007 page1)