Mathur also knew from her own work analyzing the gas makeup of the breath from bariatric surgery patients that those releasing higher levels of methane in their breath tended to have a body mass index (BMI) nearly seven points higher on average than those with lower levels.

CNN: Can you smell obesity?

And sure enough, Mathur found that among the nearly 800 participants she tested, those with higher levels of methane (three or more parts per million over 90 minutes) and hydrogen gases (20 or more parts per million) in their breath also tended to be heavier, with a BMI about 2.4 points greater than those with normal levels of the gases and about 6% more body fat on average.

CNN: Can you smell obesity?