Maybe a lot of thin people will be worried about their health if the inside fat matters.

    Some doctors now think that the inside fat around important organslike the heart or liver could be as dangerous as the outside fat which can be noticed more easily.

    "Being thin doesn't surely mean you are not fat," said Dr Jimmy Bell at Imperial College. Since 1994, Bell and his team have tested nearly 800 people with MRI to create "fat maps" showing where people store fat.

    According to the result, people who keep their weight through the food they usually eat rather than exercise are likely to have major deposits (堆积物) of inside fat, even if they are thin.

   Even people with normal Body Mass Index (体重指数) scores can have surprising levels of fat deposits inside. Of the women, as many as 45 per cent of those with normal BMI scores (20 to 25) actually had too high levels of inside fat. Men were nearly 60 per cent.

    According to Bell, people who are fat on the inside are actually on the edge of being fat. They eat too many fatty and sugary foods, but they are not eating enough to be fat. Scientists believe we naturally store fat around the stomach first, but at some point, the body may start storing it elsewhere.

    Doctors are unsure about the exact dangers of inside fat, but some think it has something to do with heart disease and diabetes (糖尿病). They want to prove that inside fat does harm to the body's communication systems.

    The good news is that inside fat can be easily burned off through exercise or even by improving your eating habits. "If you want to be healthy, there is no other way. Exercise has to be an important part of your lifestyle," Bell said.