ARE YOU REALLY OVERWEIGHT?

It could soon replace the Body Mass Index (BMI) calculations which most professionals currently rely on to judge the state of our bodies.

And it could bring new hope to dieters who lose heart and abandon their treks to the gym because their efforts never seem to be rewarded with weight loss – quite often because their efforts are building muscle which is heavier than fat.

Bioelectrical Impedance Analysis works by sending an electrical signal through the body between electrodes held in each hand.

The strength of the signal depends on what kind of body tissue it encounters.

Because muscle and blood contain high levels of water and electrolytes they conduct the signal well. Fat, by contrast, contains little water so it weakens the signal.

Therefore, the more fat you are carrying the weaker the signal will be and the high tech "scales" provide a readout that takes into consideration gender, age and height.

According to BMI a quarter of the UK population is clinically obese but BMI, devised more than 150 years ago, compares only height and weight and makes no allowance for "non-average" muscle make-up.

Consequently many athletes, typically heavily-muscled rugby forwards, will set obesity alarm bells ringing even though they carry very little fat tissue, while elderly people who have lost much of their muscle structure may register within "normal" limits, even though they are quite dangerously fat.

Dr Susan Jebb, of the Medical Research Council explained: "Weight is just one part of the equation but how heavy you are isn't as critical as how fat you are."

GP Dr David Haslam said: "A lot of patients become disillusioned and give up exercise.

"BMI is an incredibly crude tool that needs to be consigned to the waste bin. It just doesn't measure risks or progress in the individual.

"While BIA isn't perfect, it does enable them to see how their body composition is changing."