Gas chromatography separates components of a mixture to detect specific substances, and has been used previously to quantify nitrosoproline. The addition of mass spectrometry to the analysis allowed for determination of the chemical structures of molecules in the sample - in this case, the presence of a specific compound that is released in urine after garlic is eaten.

When the test was used on the urine samples from the pilot garlic study, it showed that the participants who had taken garlic had lower concentrations of the marker for nitrosation than did those who took no garlic. Though the differences were slight, the consumption of 5 grams of garlic per day was associated with the lowest level of the marker for potential carcinogens. A single garlic clove typically can weigh between 1 and 5 grams.

Vitamin C had a similar effect in lowering the marker for nitrosation.

Harrison, also an investigator in the Center for Advanced Functional Foods Research and Entrepreneurship at the Ohio Agricultural Research and Development Center, noted that previous research has suggested that garlic and other plants with sulfur-containing compounds offer a variety of potential health benefits. Many questions remain about exactly what those benefits are and precisely how garlic works as a nutritional intervention.

"The precise mechanism by which garlic and other compounds affect nitrosation is under extensive investigation, but is not clear at this time," he said.

"What this research does suggest, however, is that garlic may play some role in inhibiting formation of these nitrogen-based toxic substances. This was very small pilot study, so it's also possible that the more garlic you have, the better it would be.

"So if you like garlic and you like garlic-containing foods, go out and have as much as you want. There's no indication it's going to hurt you, and it may well help you."