Gastrointestinal colonization with methanogens increases difficulty of losing weight after bariatric surgery

Mar 9 2015

A new study finds that after weight loss surgery, people whose breath has high concentrations of both hydrogen and methane gases have a lower percentage weight loss than other bariatric surgery patients do. The study results will be presented Thursday at the Endocrine Society's 97th annual meeting in San Diego.

"Our new study suggests that gastrointestinal colonization with methanogens makes it harder to lose weight after bariatric surgery," said lead investigator Ruchi Mathur, MD, director of the Diabetes Outpatient Treatment and Education Center at Cedars-Sinai, Los Angeles.

The investigators previously correlated high breath levels of both hydrogen and methane with a higher percentage of body fat and a higher body mass index (BMI), which is a measure of weight adjusted for height. Their research focused on whether there is an association between obesity or metabolic dysfunction and gut microbes that produce methane, called methanogens.

A test for the pattern of gases in exhaled breath is a surrogate for gas-producing intestinal micro-organisms, which reside in the gut, according to the researchers.

Mathur and her colleagues studied 156 obese patients (112 women and 44 men) who had undergone bariatric surgery with either gastric bypass or gastric sleeve surgery four to 12 months earlier. For equal comparison, the researchers normalized the BMI and weight change data to be at six months postoperatively for all patients. Patients were excluded from the study if they had any chronic disease, or were taking any medication, that could change gut micro-organisms.

Each patient had a single breath test. The researchers used standard cutoffs for methane of three or more parts per million (ppm) and hydrogen of 20 ppm or more to determine positive (high) test results. Thirteen patients had positive tests for both gases, according to the investigators.

These 13 patients reportedly had an average percentage decrease in BMI of only 20.6 percent compared with an average 23.5 percent BMI reduction for the other 143 patients.

Similarly, the group with high levels of methane and hydrogen had a significantly lower percentage change in weight on average: 20.0 percent of weight lost versus 23.9 percent in the other group. The difference was statistically significant and remained significant when the researchers made the cutoff 10 ppm or more for hydrogen, which is the fuel source for methane. Eighteen patients met this criterion plus having a positive methane test; they had an average 20.1 percent weight loss versus a 24 percent decrease in weight for the other group.

Mathur theorized that an overgrowth of the main methane-producing micro-organism, Methanobrevibacter smithii, may alter a person's metabolism in a way that causes that person to be more likely to gain weight or less likely to lose it. She said it is possible, however, to alter the person's mix of gut microbes through dietary changes or, in the future, use of medications currently under development.

"We believe such interventions will help these patients achieve their weight loss goals after bariatric surgery," Mathur said.

Source: The Endocrine Society