The Scoop On Poop: Potential Benefits of Gut Microbiota

Emory Hsu, MD

We humans are often preoccupied with our outward appearance. But how often do we give any thought to our gastrointestinal tract? Certainly, we talk about gut instincts, gut reactions, but remain remarkably ignorant of what is really going on in this part of our bodies.

As it turns out, perhaps we should be paying more attention (as unsavory as the thought might be). Scientists are discovering that the trillions of non-human cells (bacteria, viruses and fungi) that inhabit our gut – so numerous that they weigh approximately the same as the human brain – play a huge role in our well-being, with our poop potentially holding the key to treatment for bowel disorders, mental health issues and even obesity.

It’s only been in the past few decades that researchers have begun to realize the vast positive health effects of this complex community of living organisms, now commonly called microbiota, and have been working on new methods of boosting beneficial gut bacteria. Among the developments are prebiotics, a non-living supplement (usually non-digestible dietary fibers or fermented nutrient mix), that specifically changes the gut microbiota composition by nourishing the good bacteria already in the large bowel or colon, thereby improving the good-to-bad bacteria ratio.

Alternatively, probiotics are live bacteria and yeasts that are good for your health (especially the digestive system) that can be introduced to the body via supplements as well as foods that are prepared by bacterial fermentation, such as yogurt, kefir, tempeh and kimchi. They can be effective in reducing inflammation and disease severity in conditions such as ulcerative colitis and Crohn’s disease, although not all probiotics work equally effectively. It’s important to note that the strains of bacteria used in probiotic supplements are not sourced from human waste; rather they are strains that were originally extracted from healthy human stool samples during early probiotic research and cultured under controlled laboratory conditions.

Perhaps the most interesting (and newest) method of introducing live microorganisms into the body is through human feces. Fecal microbiota transplant (FMT) – where feces is taken from a carefully screened donor, mixed with saline and placed into the intestinal tract of a patient – has been studied extensively as therapy for difficult-to-treat intestinal infections caused by a bacteria called Clostridium difficile (C. diff). The procedure is meant to restore the “good” bacteria from the donor into the patient. The irony is that these patients often become severely ill in the first place because antibiotics meant to destroy the bad bacteria end up destroying the good bacteria as well, which paves the way for the C. diff infection.

Scientists are also studying how changes in gut bacteria may affect obesity. About a decade ago, researchers started investigating how changes in microbiota may impact our weight and discovered increases or decreases in different types of bacteria are associated with obese or lean body size. However, whether the association of specific bacteria and a lean body means that that bacteria is causing weight control is hotly debated in scientific circles – it could just mean that the foods the person is eating are foods that are lower in calories and these foods are what make the specific bacteria flourish, or that the person’s own genetics direct food processing and what bacteria are in the gut. The jury is still out on this topic.

Additional insight about microbiota’s impact is coming from studies of antibiotic use which, in certain instances, seem to affect body weight. However, research in mice suggests the weight change is not a direct effect of antibiotics, but rather is from the changes in gut microbiota. Studies looking at people born via cesarean section (thus having been exposed to different flora than through vaginal birth), as well as those treated with antibiotics in their childhood, suggest some moderate associations with body mass.

And after gastric bypass, in circumstances where patients have not lost much weight following the surgery but whose blood sugar levels become much more controlled and are even able to come off medications like insulin, it is now thought that microbiota may be partially responsible for this rapid change in metabolism. Ongoing studies are looking at transferring stool from lean donors to obese individuals to examine their microbiota changes and the effects on the person’s metabolism. A note of caution is in order, however: this does not mean that exchanging feces might be a cure for obesity. A number of factors beyond microbiota are at play with the disease.

Yet other studies suggest a link between microbiota changes and conditions as diverse as depression, non-alcoholic fatty liver disease and rheumatoid arthritis. However, these links are not clear cut and do not yet provide the strong scientific evidence needed to establish an absolute causal link. Further research is needed before definitive recommendations can be made.

Studying microbiota has proven to be difficult, and not just because of their sheer number and diversity. Microbiota are sensitive to changes in diet, sleep, exercise, stress and other factors. Plus, within a species (E. coli, for example), some strains can be beneficial, while others are harmful. Even the same strain can have different effects when in different parts of the body. This obviously presents challenges to any researcher.

What is indisputable, though, is that there is a strong interdependency between humans and the trillions of other beings living in us. Now it’s up to scientists to determine how we might use these microorganisms to maximum benefit.

Dr. Emory Hsu is conducting research on osteoporosis and microbiota at Emory University in Atlanta, Georgia. He graduated with an undergraduate degree from Harvard University and from medical school at Vanderbilt University, during which he was a Howard Hughes Medical Institute “Cloisters” Research Scholar for a year at the National Institutes of Health near Washington, D.C. He completed his Internal Medicine residency at Emory University, where he is now an Endocrine Fellow.