Scanner could reveal hidden fat

The scan can pinpoint the exact distribution of

A body scanner could help fitness fans work out exactly how much of their bodies are made up of fat.

Doctors could use the device - developed by UK scientists - to look for abnormal fat which may be putting their patients at risk.

Scientists at Lancaster University and the Institute of Food Research in Norwich used radiowaves to detect fat beneath the skin.

It is hoped that such machines could be commonplace in leisure centres one day.

The device works on the principle that the human body is a mixture of water and fat.

The amount of fat on a person can be calculated by working out their density using their exact volume and weight.

Other methods pass a tiny electrical current through the body - the level of resistance to the current can be used to estimate fat content.

However, none of these methods is particularly practical to be used in seriously-ill patients - or ordinary members of the public who need an easy way to find out the truth about their bodies.

Field method

The new method, revealed in New Scientist magazine, involves passing coils which create a radio-frequency electromagnetic field over the body.

The make-up of the object within the coil alters the phase of the field - and this can be measured and used to estimate the water content - and hence the fat content.

We should be able to put something like this in a leisure centre and members of the public could use it on a regular basis Dr Henri Tapp, Institute of Food Research

When this information is coupled with an exact measurement of the body's volume collected by four lasers sweeping across it, the researchers can in theory create a rough picture of not only the amount of fat, but also its location on the body.

Dr Henri Tapp, from the Institute of Food Research, told BBC News Online: "The technique is called magnetic induction tomography - it has been around for a while, but it is the first time it has been used this way.

While traditional measures of obesity, such as body mass index, can help doctors predict the risk of diseases such as diabetes or heart disease, there is increasing evidence that the precise location of that fat - whether it evenly distributed or located around the waist - also has a bearing.

'Fat scan' shows up health risk

Fat appears white on the MRI scan

A scan can spot which people harbour dangerous levels of fat around their vital internal organs, scientists say.

Hammersmith Hospital, in west London, is currently the only hospital in Europe using the MRI scan.

Its scientists say 40% of the population have "bad" fat around the heart, liver or pancreas, even though many appear thin. Only a litre of fat should surround these internal organs. People who are thin but do little exercise often exceed this amount.

They warn it is possible to be slim and yet still be at risk of conditions like diabetes because of "hidden" fat.

Evidence suggests the precise location of fat has more of a bearing on health than simply being overweight.

For example, people who have too much weight around their middle, often called an "apple" shape, have a greater risk of developing heart disease and type 2 diabetes than those who are pear shaped and carry the weight around the hips.

Fat is good in general, but when you have too much of it or fat in the wrong places it is bad Researcher Professor Jimmy Bell 'I'm fat on the inside'

While doctors can check whether a person is a healthy weight for their height by calculating their body mass index or BMI (weight in kilograms divided by height in metres squared), they cannot see the dangerous hidden fat.

Lead researcher Professor Jimmy Bell, a Medical Research Council scientist, explained: "One of the problems with BMI is it gives you the wrong idea of how much fat you have.

"It's about where you have the fat.

"Fat is good in general, but when you have too much of it or fat in the wrong places it is bad.

"Someone can look really thin and have a normal BMI but have seven litres of fat inside them when they should ideally only have one litre."

Once doctors are aware someone has dangerous levels of hidden fat, they can work out the right combination of exercise and healthy eating needed to shift it, Professor Bell said.

He explained: "We are trying to understand what factors - genetic and environmental - make people put on fat internally and then determine what people need to do to get rid of this fat.

"When you diet you don't lose the right type of fat. If you exercise you lose more of the bad fat.

"If people are only going to do an hour of exercise a week, let's make sure that hour is spent doing the right exercise to shift the important internal fat."