HealthDay News — Individuals with both high methane and hydrogen results on a breath test had higher body mass index (BMI) and body fat, study results indicate, suggesting a possible correlation between gut flora and obesity.

Among individuals with positive breath test results for both gases, mean BMI was 26.5 kg/m2, compared with BMIs of 24.1 kg/m2, 24.2 kg/m2, and 24 kg/m2, for those who had normal tests, were positive for hydrogen only, or were positive for methane only (P<0.02), Ruchi Mathur, MD, and colleagues from Cedars-Sinai Medical Center in Los Angeles reported in the Journal of Clinical Endocrinology & Metabolism.

Total body fat was also higher in those who tested positive for both methane and hydrogen — 34.1%, compared with 28.3% for those who were normal, 27.5% for those who tested positive for hydrogen, and 28% for those who were positive for methane (P≤0.001).

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“There is growing interest in the potential role of gut flora in the pathogenesis of obesity,” the researchers wrote. “Our results may support this hypothesis, as the presence of both hydrogen and methane on breath test, but not either methane or hydrogen alone, is associated with higher BMI and percent body fat, perhaps because these subjects have an abundance of hydrogen to fuel methane production.”

Animal studies have found an association between colonization with M. smithii and weight gain, and Mathur and colleagues previously observed higher levels of exhaled methane in obese patients. To further explore the association, the group enrolled 792 consecutive patients referred for lactulose breath testing due to abdominal symptoms to participate in the study.

Participants were administered 10 mg of lactulose syrup and 250 mL of water and breath samples were recorded every two hours. Results were considered positive with methane levels of at least 3 parts per million and hydrogen levels of 20 parts per million.

A total of 28 participants tested positive for both methane and hydrogen, the researchers found. Participants who tested positive tended to be older, male and report problems with constipation compared with those who tested negative.

The researchers called for more studies to examine the interaction between gut microbiota, metabolism and obesity.

Study limitations include lack of information about patient’s dietary habits and ethnicity, two factors which play a role in the interaction between gut microbiota and host.


  1. Mathur R et al. J Clin Endocrin Metab 2013; doi: 10.1210/jc.2012-3144.