US scientists believe they may be able to develop a more reliable lie-detector test - by listening to liars' stomachs.

Conventional polygraph tests, which are 80 to 90% accurate, use changes such as increased heart rates and sweating.

But people who are telling the truth can show similar changes merely because they are anxious about being tested and others learn how to "cheat" the tests.

A University of Texas study involving 16 people found looking for gut pattern changes was a more reliable test.

Dr Pankaj Pasricha and colleagues told an annual meeting of the American College of Gastroenterology how their test, called an electrogastrogram (EGG), could clearly spot when someone was telling a fib.

They asked 16 volunteers to simultaneously undergo EGG tests and standard electrocardiogram (ECG) - a test to measure heart rate which makes up part of standard polygraph testing.

Like an ECG, an EGG is recorded by attaching painless electrode stickers to the skin.

Gut reaction

The researchers found that both lying and telling the truth affected the ECG recordings compared to baseline measurements when the volunteers were asked simply to rest.

In comparison, the EGG showed obvious changes only when the individual was telling a lie - there was a big decrease in the percentage of normal gastric slow waves.

"Further research in real-life situations and using larger numbers is necessary to validate these results," cautioned the authors.

However, they said their findings suggested: "The addition of the EGG to standard polygraph methods has clear value in improving the accuracy of current lie detectors."

Professor Richard Wiseman, a psychologist at the University of Hertfordshire, said: "It is an interesting idea.

"However, like the conventional lie detector, the technique seems to rely on the notion that people become more stressed when they lie.

"People who do not feel guilty about lying or have rehearsed the lie many times may not show such anxiety and thus pass the test."

Professor Don Grubin, professor of forensic psychiatry at Newcastle University, said: "There's no reason to believe that this would not work.

"The stomach is controlled by the same bit of the non-voluntary nervous system that controls breathing and heart rate and sweating. So we would expect to see changes.

"But a lot more work is needed to determine whether these changes do provide added value."

He said that conventional lie detectors were between 80 and 90% accurate and that, as yet, there was nothing available to beat that.