Researchers trying to figure out if microbes living in your body might be a factor in weight gain say a breath test could show if you’re loaded with greedy germs that pull every last calorie out of food.

Study after study is showing that people are covered in bacteria, fungi and other microorganisms that help digest food, that can keep teeth healthy and even that cause dandruff. And they’re finding that the types of microbes living in the colon and intestines may play a major role in just how much nutrition the body gets out of food. …

Mathur and colleagues were looking at a species of bacteria called Methanobrevibacter smithii – M. smithii for short. As its name indicates, it makes a lot of methane – the odorless gas responsible for burps and other inconvenient emissions.

People who produced the most methane and another gas, hydrogen, in their breath weighed more and had more body fat than people who produced the lowest amounts, they reported in the Journal of Clinical Endocrinology & Metabolism.