Updated: Jun 6
Most of your cells aren’t human. In fact, most of your cells aren’t even yours! Only approximately 10% of the cells in your body are human, which begs the question: what else is living in you?
The gut microbiome is one of the most impactful communities of nonhuman cells living inside you. The average human adult can host up to two kilograms of these cells in their gut. They are unique to each and every person; no two microbiomes are the same. But what exactly is a gut microbiome?
According to the Merriam-Webster Dictionary, the gut is “part of the digestive tract and especially the intestine or stomach”. A query in the same dictionary of the word “microbiome” results in the definition: “a community of microorganisms (such as bacteria, fungi, and viruses) that inhabit a particular environment and especially the collection of microorganisms living in or on the body”. In simpler terms, your gut is where all your digestion happens, and a microbiome is a bunch of germs. So by putting these two definitions together, we can conclude that the gut microbiome is just a little village of germs living in your intestines.
So how did this little imposter village of germs even get into you in the first place?
According to a study published by the National Institutes of Health, or the NIH, the first microbes are introduced to infants immediately after birth. Infants born via regular birth are found to have many of the same microbes as present in the mother’s mouth and gut, and further gain their mother's microbes through breastfeeding. Infants born via caesarean section are found to contain more bacteria present in hospital settings, including those demonstrating antimicrobial resistance. These antimicrobial strains are thought to be linked to the high number of c-section born infants that suffer from asthma, allergies, and other immune conditions. However, the gut microbiomes of caesarean born infants are quickly replenished by breastfeeding, which provides them with their mother’s healthy microbes. As infants are further exposed to the outside world, they gradually collect bacteria in their gut, and within a year, there is no noticeable difference in the gut microbiomes between caesarean and non-caesarean born infants.
But why are the types of bacteria present in your gut relevant?
Studies in past years have shown links between the gut microbiome and obesity, cancer, mental health, and autism.
A 2014 study conducted by researchers from King's College (London, UK) and Cornell University (Ithaca, New York) found that Christensenellaceae minuta, a strain of bacteria highly influenced by genetics, was often found in people with lower body weights. When the researchers introduced Christensenellaceae minuta to mice, they found that the mice it had been introduced to actually gained less weight than those without. Another 2012 study published by the Journal of Proteome Research indicates that bacteria found in the large intestine can protect against weight gain by increasing the activity of brown fat. Brown fat burns calories and white fat when stimulated, preventing obesity. Furthermore, a case report published by Open Forum Infectious Diseases describes how a woman who received a fecal microbiota transplant from an overweight donor began gaining weight after the operation herself. While further research is necessary for a sound conclusion, these studies bring to light a potential link between the gut microbiome and preventing obesity.
As for cancer, bacteria in the gut microbiome are found to both increase likelyhood of cancer, as well as improve the outcomes of cancer treatment. A 2013 study published by the Journal of Cancer Research claims that Lactobacillus johnsonii, a strain of bacteria found in the large intestine, may affect the development of white blood cell cancer, or lymphoma. Another 2013 study conducted by researchers in the UK shows that Helicobacter pylori, a bacteria commonly found in the gut, is capable of deactivating the part of the immune system responsible for regulating inflammation, causing ulcers and stomach cancer. Furthermore, a 2014 study conducted by researchers at Icahn School of Medicine at Mount Sinai (New York City, New York) and published by the Journal of Experimental Medicine indicates that gut microbes may also play a role in colorectal cancer. However, while the gut microbiome is linked to various forms of cancer, it has also been found to aid cancer treatment! A 2013 study published by researchers from the National Cancer Institute shows that cancer treatments such as immunotherapy and chemotherapy worked significantly better on mice with normal gut microbiomes, rather than mice with reduced gut bacteria. A similar 2013 study conducted by French researchers found that mice with normal, diverse gut microbiomes responded much better to cyclophosphamide, an antitumor drug, in comparison to mice with less diversity in their gut bacteria.
Physical effects aside, the gut microbiome has been found to impact mental health as well. Various studies have lead researchers to believe that there is a connection between mental health issues such as depression or anxiety and the gut microbiome. Dr. Kirsten Tillisch, the lead author of one of such studies, explains that she "hear[s] from patients that they never felt depressed or anxious until they started experiencing problems with their gut". In addition, in 2013, researchers from Arizona State University discovered a link between the gut microbiome and autism: children with autism were found to have less Prevotella, Cocprococcus, and Veillonellaceae bacteria in their gut in comparison to children without autism. While further research is required to reach a sound conclusion, it is evident that the gut microbiome is inextricably linked with the brain.
Clearly, a flourishing gut microbiome is crucial to living a healthy, happy life. So what can we do to set it up for success?
In order to improve or maintain your gut health, Medical News Today recommends the following: taking probiotics, eating fermented foods (kefir, kimchi, kombucha, miso, sauerkraut, tempeh), eating prebiotic fiber (asparagus, bananas, chicory, garlic, Jerusalem artichoke, onions, and whole grains), reducing stress, avoiding unnecessary antibiotics, exercising regularly, getting enough sleep, and avoiding smoking. Of course, it is not necessary to implement every single suggestion into your daily life, but just remember: a happy gut microbiome is vital to creating a happy life!
In summary, the gut microbiome is a village of bacteria living in your gut that has been collected throughout your life. The types of bacteria present determine important traits, such as obesity, cancer risk, reception to cancer treatment, mental state, and possibly even disorders such as autism. In order to protect and enhance your gut microbiome, probiotics, prebiotic fibers, and fermented foods are recommended, as well as enough sleep, exercise, and stress management.
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Devlin, Hannah. “Caesarean Babies Have Different Gut Bacteria, Microbiome Study Finds.” The Guardian, Guardian News and Media, 18 Sept. 2019, www.theguardian.com/society/2019/sep/18/caesarean-babies-have-different-gut-bacteria-microbiome-study-finds.
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