Obesity may be linked to microorganisms.

• Position: YOUR LIFE

How much a person eats may be only one of many factors that determine weight gain. A study by Cedars-Sinai Medical Center, Los Angeles, Calif., suggests that a breath test profile of microorganisms inhabiting the gut might be able to tell physicians how susceptible an individual is to developing obesity. The study shows that those whose breath has high concentrations of hydrogen and methane gases are more likely to have a higher body mass index and higher percentage of body fat.

"This is the first large-scale human study to show an association between gas production and body weight--and this could prove to be another important factor in understanding one of the many causes of obesity," notes lead author Ruchi Mathur, director of the Diabetes Outpatient Treatment and Education Center in the Division of Endocrinology.

Based on the breath tests, four patterns emerged: the subjects either had normal breath content; higher concentrations of methane; higher levels of hydrogen; or higher levels of both gases. Those who tested positive for high concentrations of both gases had significantly higher body mass indexes and higher percentages of body fat.

The presence of methane is associated with a microorganism called Methanobrevibacter smithii, which is responsible for...