Currently, researchers worldwide are studying the contribution of the gut microbiota (the 100 trillion bacteria that reside in our gut) to human health and disease. In the United States, the Human Microbiome Project is making a dent in this broad field of study, with researchers discovering how little we really know about this vast population that lives within and on us, helping to shape our health, or lack thereof. In addition, other research groups independent of the Human Microbiome Project are studying the link between our gut inhabitants and our health.

A recent study published in the Journal of Clinical Endocrinology and Metabolism has contributed to our further understanding of this vital gut connection.1 Researchers from Cedars-Sinai Medical Center analyzed data from almost 800 people and found that increased body mass index (BMI) and percent body fat were linked to the presence of methane and hydrogen gasses as measured by a breath test, suggesting that the presence of a methane-producing microbe—Methanobacter smithii, the most prevalent methane producer in the gut—is perhaps contributing to the weight gain.

The lead researcher Ruchi Mather, MD stated, “Usually, the microorganisms living in the digestive tract benefit us by helping to convert food into energy. However, when this particular organism—M. smithii—becomes overabundant, it may alter this balance in a way that causes someone to be more likely to gain weight. Essentially, it could allow a person to harvest more calories from their food.”

Another interesting explanation in the paper, which was not reported in media articles that summarized the results, is the possible effect of methane on bowel habit. The researcher previously noted an associated between breath methane and constipation (constipation-predominant irritable bowel syndrome), and found that methane gas slowed gut transit (the time it takes food to travel through the digestive tract—slow gut transit is what happens when you’re constipated) in an animal model.

They stated, “We hypothesize that the slowing of transit could result in greater time to harvest nutrients and absorb calories, representing another potential mechanism for weight gain. They are saying, essentially, that constipation could make you fat. Indeed.

The researchers are continuing to study the effects of M. smithii on obesity and prediabetes to confirm this link in another study funded by the American Diabetes Association. Mathur stated, “We’re only beginning to understand the incredibly complex communities that live inside of us. If we can understand how they affect our metabolism, we may be able to work with these microscopic communities to positively impact our health.”

The gut connection to metabolic disorders, including diabetes and obesity, will likely change the way we treat these conditions, which are currently at epidemic proportions. Stay tuned as researchers get closer to understanding the intricate happenings in the human digestive tract.



  1. R. Mathur, et al., “Methane and hydrogen positivity on breath test is associated with greater body mass index and body fat.” J Clin Endocrin Metab. 2013 March; doi: 10.1210/jc.2012-3144.