Scientists in Japan claim to have developed a pocket-sized sensor that provides a readout of how much fat a person burns while they exercise. A study on the device's capabilities was published on Wednesday in the Journal of Breath Research.

"Because obesity increases the risk of lifestyle-related illnesses, enabling users to monitor the state of fat burning could play a pivotal role in daily diet management," said senior author Satoshi Hiyama of NTT DOCOMO Research Laboratories. "Current standard methods, however, are still not practically suitable for point-of-care instrumentation for diet-conscious people who wish to monitor their own fat metabolism at home or outside."

The device works by measuring the levels of acetone expelled in people's breath. Acetone is a natural byproduct that is produced when cells use fat for fuel through a process called ketosis. The breathalyzer, which is about four inches long and weighs about as much as a smartphone, can detect subtle variations in exhaled acetone.

Hiyama and his colleagues tested the device on 17 healthy volunteers, who were split into three groups. The first group went about their normal daily routines. The second group added a 30-60 minute session of light exercise (jogging or fast-walking) to their daily schedule, and the final group exercised and dieted.

Every morning for two weeks, each subject measured their acetone levels with the breathalyzer, which sent the recordings to their Android-based smartphones.

Only the third group (diet and exercise) recorded a significant change in acetone. This change correlated with a drop in body fat content, which was measured with a bath scale.

"Considering that the effect of dieting could be estimated from changes in breath acetone concentrations, we've shown that our prototype is a practical and alternative checker that can be used in individual dieting programs," concluded Hiyama.

"It is also known that when diabetes is out of control, patients have elevated levels of breath acetone. It is possible that our prototype could be used to assess how diabetic control is being managed at home."

Source: Toyooka T, Hiyama S, Yamada Y. A prototype portable breath acetone analyzer for monitoring fat loss. Journal of Breath Research. 2013.