Field of Science

A correlation between gut bacteria and obesity.

Those of you who know me well know that I enjoy learning things by studying poop, and one of the great things in poop that we can exploit is the remnants of gut bacteria. A healthy bouquet of bacteria is necessary for proper digestion and intestinal function. The bouquets vary from person to person, and the causes and consequences of interpersonal variation in gut bacteria communities aren't very well understood. However, there are some correlations. Studies in mice and humans show that individuals with less diversity in their gut bacteria tend to be obese, and that certain types of bacteria seem to be present more often in obese individuals. This effect could be stimulated in mice by feeding them antibiotics, which kill off portions of the gut bacteria, and the mice treated with antibiotics had more body fat than non-treated mice. In addition to obesity, people with less diversity in their gut bacteria (measured by quantifying the bacterial DNA in stool samples) also were more likely to be resistant to insulin, a symptom of type II diabetes which is also often correlated with obesity.

It has always been assumed that the gut bacteria will "bounce back" or spontaneously re-colonize the gut after an antibiotic regimen or a brief infection, but some people are starting to question this assumption. Post-infectious irritable bowel syndrome is believed to be caused by a disruption of the gut flora following a bout of gastroenteritis. The idea is that the infectious bacteria flush out the good bacteria by competition or flushing with diarrhea. A popular treatment for this imbalance in gut bacteria is to take probiotics, either in pill form or in the form of active culture yogurt and dairy products. However, most of these products only contain one or two species of known gut bacteria. It seems that a healthy digestive system is associated on a diverse bouquet, which could potentially be problematic if we're overloading our guts with only a few species of bacteria, but is unknown as to whether gut bacteria is a factor in causing obesity or if it is somehow a result of obesity.

ResearchBlogging.orgPennisi, E. (2011). Girth and the Gut (Bacteria) Science, 332 (6025), 32-33 DOI: 10.1126/science.332.6025.32


  1. I recall reading somewhere that the main function of the bacteria present in probiotics is to colonize the space vacated by the gut flora temporarily - to prevent various nasty critters (like Clostridium difficile) from taking residence. Then the normal bacteria gradually grow back, restoring diversity. It's late so I'm including just this search result, feel free to dig deeper and correct me if I'm wrong.

  2. So the obvious question is what are the good gut microbes and how might I get some?

  3. I'd love to find the bacteria that used to allow me to digest onions, leeks and massive doses of garlic. Clearly I lost them when I had a round with peritonitis. Unfortunately I hadn't banked my microbiota years ago when I could eat anything under the sun. I'm a little leery of transplanting other people's microbiomes just yet.

  4. Awesome research Michelle! We have a section in our book about this! Living with Crohn's & Colitis: A Comprehensive Naturopathic Guide for Complete Digestive Wellness.... why doesn't the mainstream IBD community endorse this research? I have been in remission for almost five years, due to a balance of gut microbial -- good and bad bacteria. I take daily probiotics that I get from a licensed naturopathic doctor with a 4 year med degree. Thanks again.

  5. To my knowledge, most doctors do support the use of probiotics for certain GI problems. My gastroenterologist is who suggested that I start taking probiotics for my IBS. I haven't seen any results yet, but it's only been a week and a half...


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