London, Jan 23 (Agencies): British scientists have developed a new breathalyzer that they claim can tell how much fat you are burning off at the gym.

The device, according to researchers, can pinpoint the moment when a sweaty session on the treadmill finally starts to pay off by detecting when the body has used up its supply of food energy and switches to breaking down fat instead.

Exercise machines currently estimate when people have entered the "fat burning zone".

Professor Gus Hancock, an Oxford University chemist who developed the machine, said it works by picking up minute changes in the levels of a molecule called acetone in people's breath, which is given off when the body starts to burn fat.

"Acetone is a molecule that is produced by people who are burning fat rather than food," he was quoted as saying by the Telegraph.

Prof Hancock began working on the breathalyzer technology in the hope of developing a way of screening patients for diabetes, which creates elevated levels of acetone in breath.

According to him, the device works by using a detection method known as spectroscopy which measures the wavelengths of light that are absorbed by different molecules in a gas.

Professor Hancock said: "We started thinking that our techniques could be applied to the detection of different chemicals in human breath and would that be useful if there was a correlation between the gases in human breath and disease.

"When you are ill, the concentrations of different molecules change. Acetone is associated with diabetes and we have already developed a detection system that can see acetone at about the levels that are important for the diagnosis of diabetes.

"We would like to set this up as a screening method for diabetes as there are so many people who suffer from it, particularly type II diabetes, but they don't know they have it."

At present diabetes is diagnosed using a blood test that has to be sent to a laboratory for analysis but a breath test would allow patients to be diagnosed in their doctors surgeries without having to give blood.