NEW YORK (Reuters Health) - Each strand of hair on the head holds a record of a person's eating habits -- a fact that may allow doctors to objectively diagnose eating disorders, preliminary research suggests.

Scientists at Brigham Young University have developed a test that may be able to diagnose anorexia and bulimia by analyzing the nitrogen and carbon content of just a few strands of hair.

Right now, diagnosis of these disorders relies heavily on the patients' honesty about their eating habits and body image. This is a significant obstacle because women with anorexia or bulimia often deny that they have a problem.

An objective measurement such as the new hair test could help confirm a suspected eating disorder, according to the study authors.

"The clinician could confront the patient with hard data," said lead author Dr. Kent A. Hatch. As it stands, he noted in an interview, "it's oftentimes hard to convince them that they have an eating disorder."

What's more, Hatch said, hair analysis could help doctors monitor eating disorder patients' recovery or catch signs of relapse.

He and his colleagues at the Provo, Utah, university report their findings in the journal Rapid Communications in Mass Spectrometry.

For hair to grow, proteins have to be added to the base of the strand, and the composition of these proteins is influenced by diet. So each strand essentially contains a record of dietary intake over time.

For their study, Hatch and his colleagues measured the carbon and nitrogen ratios in hair samples from 20 women with anorexia, bulimia or both, and from 23 healthy women. They found that the test was able to identify those with an eating disorder 80 percent of the time.

Still, the test is probably several years away from being used in practice, Hatch said. More research, he explained, is needed to see what the test's limitations might be -- such as whether it might pinpoint vegetarians or vegans as having an eating disorder.