Did you know that bacteria make up the majority of your poop??
Yep, that’s right. Roughly 60% of the dry weight of your feces comes from bacteria.
Sounds kind of crazy, right?
But actually, these gut bacteria are more important than you might think.
They live within our intestines, and we have a pretty neat mutualistic relationship with them (both the bacteria and ourselves benefit).
We provide the bacteria with food (undigested remnants of what we ate), and the bacteria do the following for us:
- Create vitamins! Gut bacteria are most famously known for producing vitamin K2 (an essential vitamin critical for blood clotting), which we absorb from the gut into our blood stream, but they also produce smaller amounts of biotin, vitamin B12, folic acid, and thiamine.
- Break down fiber & keep our gut lining strong. Humans lack the digestive enzymes to break down the fiber found in plant foods. Luckily, the bacteria in our gut take care of that job. Once the undigested fibers reach the large intestine (where most of our gut bacteria live), they get to work breaking down the fibers and producing short chain fatty acids (butyrate, propionate, and acetate), which lowers the pH of the gut, creating an environment less favorable to pathogens. Butyrate is used as an energy source by the cells that line your colon (known as colonocytes). Some studies suggest that ulcerative colitis (an inflammatory disease that causes ulcers in the colon) is associated with low levels of butyrate-producing bacteria, and that eating more fermentable fibers (like those found in oat bran) can increase butyrate concentrations in the colon and reduce abdominal pain & reflux. So feeding those butyrate-producing bacteria is important!
- Break down & recycle compounds. Some compounds that are metabolized in the liver and then secreted into the gut (ike bilirubin and bile acid, cholesterol, estrogens, vitamin D metabolites, and some medications), are broken down by the gut bacteria into new forms that can be reabsorbed through the gut wall and sent back to the liver. This process saves the body so much time and energy, since it can essentially “recycle” these components and not have to build them from scratch again.
- Protect us from pathogens. The ecosystem of gut bacteria is relatively stable. The good bacteria that live there want to stay there, and actively fight off the colonization of other pathogenic bacteria and parasites. Thanks gut bacteria!
- Keep our immune system strong. When we are infants, the lymph (immune) tissue in the gut learns to recognize healthy gut bacteria that lives there, and will not mount an immune response against them. In contrast, when a new type of bacteria enters the body, the immune system recognizes it as foreign and launches an attack against it. Without the hundreds of species of healthy gut bacteria living in our bodies, the immune system would have a much greater likelihood of launching an unnecessary immune response against harmless bacteria. There is exciting new research suggesting that there is a “critical window” of colonization, during which time the gut must be properly colonized by a wide range of bacteria, or else it may increase the risk of developing atopic diseases later in life (asthma, eczema, and allergies). How fascinating is that?? PS- guess where you get a significant portion of your colonizing bacteria?? During vaginal birth. Yep. It’s exactly what you think it is. Bacteria from the mom’s vaginal area enter the mouth of the baby & colonize their gut. In contrast, infants born via C-section get their gut bacteria from the environment (the skin of the mom & nurses, the air, and the hospital environment) & tend to have a harder time colonizing their gut properly (it can take them 6 months to have a stable gut, compared to 1 month in vaginally born babies). (There is newer research suggesting that a small amount of bacteria exists in the placenta, so technically the gut is colonized pre-birth by bacteria from the mother, but environmental exposure upon birth plays a significant role.)
These awesome gut bacteria are often referred to as “the microbiome” or “microbiota”.
This name makes sense, since “micro” means “small” (and bacteria certainly are tiny!), and “biome” or “biota” means “a community of organisms that occupies a distinct region” (aka your gut).
There are up to 1,000 different species of bacteria in your gut, and they outnumber our human cells by 10:1!
So yep, there are 10x more bacteria in your gut than human cells in your entire body! (Kind of creepy!)
To put that number into perspective, that’s 100,000,000,000,000 (100 trillion) bacteria hanging out inside your intestines at any given moment.
Now here’s a key point:
The number, types, and relative proportions of these gut bacteria change over time, depending on how we treat our bodies.
When the balance of your gut bacteria gets out of whack, you have gut dysbiosis.
When you have gut dysbiosis, you may experience gastrointestinal upset (gas, bloating, diarrhea, constipation, abdominal pain), irritable bowel syndrome, decreased immunity, inflammatory bowel disease (ulcerative colitis and Crohn’s disease), or even leaky gut or small intestinal bacterial overgrowth (SIBO).
This can happen for a lot of reasons:
- Eating an unbalanced diet. Different types of bacteria feed off of different types of macronutrients. To keep all your gut bacteria healthy & happy, you need to feed them! This means you need to eat a well rounded diet containing a balance of protein, carbohydrates, fat, & fiber. If you get too crazy & eliminate (or excessively eat) one of these macronutrients, your gut will get out of whack, and you’ll feel it!
- STRESS. Are you surprised? We keep discovering more and more toxic effects of chronic stress. When you’re psychologically stressed out (worried about bills, your relationship, your job), you activate what’s known as the HPA axis (the hypothalamic-pituitary-adrenal axis), which essentially is a pathway from your brain to your cortisol-releasing adrenal glands, located on top of your kidneys. High levels of cortisol (a stress hormone) circulating around your body wreak havoc on many bodily systems, and the gut is no exception. When you’re stressed, your body assumes your life is in danger, and mundane functions like digestion are put on the back burner. The sympathetic “fight-or-flight” nervous system is in overdrive, and the parasympathetic “rest-and-digest” nervous system is out of commission. Blood is shunted away from the digestive tract and towards the muscles (you might have to run for your life, right??), and digestive health suffers. Really interesting new studies have shown changes in the gut flora of mice from exposure to social stressors and early life maternal separation. For even more ways on how stress affects the gut, check out this article.
- Consumption of antibiotics (and birth control pills?). Antibiotics can be essential and life-saving in many situations, but they do have a dark side. While they do a great job killing pathogenic bacteria inside your body that cause diseases, they ALSO kill the good bacteria! (oops, talk about throwing the baby out with the bathwater). When the antibiotics wipe out the bacteria in your gut, your body has to re-colonize with whatever bacteria enters your body. Hopefully, you are consuming probiotics (healthy bacteria that colonize the gut) via fermented foods or supplements, and providing your body with a good supply of beneficial bacteria. But if you’re not, unhealthy bacteria that make us feel yucky can take over and colonize the digestive tract. They can be tough to get rid of once they’re there, so it’s important to take probiotics in conjunction with antibiotics! Some articles online also claim that birth control pills disrupt the gut flora, but I couldn’t find any studies to back this up. Comment below if you can find something!
- Serious illness can also throw off your gut flora, even if you aren’t taking antibiotics. If you are seriously ill, you may not be eating the same diet, which could disrupt your microbiome. Certain conditions (like certain cancers, or blood pressure or blood clotting disorders) could reduce blood flow to the gut, and many diseases affect the immune system, which we know is intricately linked to the gut.
Thankfully, once you are aware of the causes of gut dysbiosis, you can make diet and lifestyle changes to boost your gut health.
Some of the best ways to nurture a healthy gut are:
- Eat (or take) probiotics. Probiotics are healthy bacteria that colonize the gut & promote a healthy gut microbiome. They can be found naturally in fermented foods like kefir, kombucha, yogurt, sauerkraut, pickles, tempeh, and kimchi. Interestingly, the word “probiotic” literally means “pro-life”, how amazing is that? It’s definitely a true statement! In order to reap the benefits of natural probiotics, it’s important to get a large enough dosage. At the very minimum, you should consume 1-2 billion cfus (colony forming units, aka live bacteria) per day. A higher dose of 5-20 billion cfus per day might be even more effective, especially if you are experiencing GI discomfort & want to establish a healthier microbiome. For some perspective, 1 bottle of G.T. Dave’s kombucha contains 2 billion cfus, and 1 cup of Lifeway kefir contains 7-10 billion cfus. You can also take probiotics in supplement form, but this is probably not necessary unless you are actively experiencing gastrointestinal distress (like irritable bowel syndrome), in which case large dose probiotics might be helpful. There are many many varieties available. VSL#3 is a super popular brand that many dietitians and medical professionals swear by. Thorne also makes a few good options: here & here.
- Take the time to de-stress. The gut is intricately linked to the brain through the enteric nervous system, and specifically, the vagus nerve. The vagus nerve runs from brain to all the organs of the body (including the gut) and delivers parasympathetic (rest & digest) messages to the organs. Basically, when the vagus nerve is activated, it tells your body to slow down, relax, and focus on resting and digesting food. As you can imagine, if you are constantly stressed out, your sympathetic nervous system is always switched on, and you never give your body the opportunity to activate the rest & digest functions of the vagus nerve. You’ll certainly still digest some food, but not at optimal levels. Try to take a few deep breaths before meals to calm yourself and activate your vagus nerve. Sit at a table, and eat from a plate, without the distraction of television or cell phones. Let yourself relax, connect with loved ones, and truly enjoy and appreciate your meal. You won’t believe how much better you’ll feel after a slow, relaxed meal compared to a meal in front of the TV or on the run. Think about the stress levels in your life, and how you can try to enjoy more relaxation time. Your gut will thank you!
- Exercise regularly. Several animal studies have found that exercise is correlated with more diverse microbiomes (yay!). These results have yet to be replicated in humans (it would be hard to study, as you can imagine), but one study of full-time rugby players found a correlation between regular exercise and a more diverse gut flora (although this could also be explained by differences in diet). Diverse microbiomes are more robust, better able to ward off infections, and help maintain a healthier gut lining. Exercise is just one component of a healthy, happy, thriving body (gut included!).
- Consume a well-balanced diet (and don’t forget about prebiotics). The biggest problem with the typical American diet is that we simply don’t eat enough plant-based foods, like fruits, vegetables, nuts, seeds, legumes, and whole grains. We tend to go heavy on processed foods (which have simple sugars but usually not much fiber. Remember, fiber is one of the essential nutrients for your gut bacteria!), meat, and fats. One of the best things you can do for your gut is make sure you are eating enough high-fiber natural foods so that all of the healthy gut bacteria can survive and thrive. Of special importance are prebiotics. Prebiotics are the food for the probiotics (bacteria). They are usually types of carbohydrates that we humans can’t digest. Foods rich in natural prebiotics include chicory, jerusalem artichokes (also called sunchokes, not the same as regular artichokes), jicama, garlic, onion, leeks, and asparagus. Want some scientific evidence that diet really can impact your gut & overall health? Although this study was conducted in mice, it shows a really cool connection between diet & asthma risk! Mice fed high-fiber diets had a healthier, more diverse microbiome that produced more short chain fatty acids, leading to a healthier gut, stronger immune system, and reduced risk of developing asthma. Amazing what diet can do!!
- Deliver vaginally and breastfeed, if possible. This is the best way to set your baby up for a healthy gut from infancy. The general template of our microbiomes is established in the first three years of life, so it’s important to create a healthy gut from the start. Breastmilk provides healthy bacteria to the infant (both directly in the milk & from the skin of the breast) and contains prebiotics (food for the bacteria) that help nurture a healthy microbiome. Formula, on the other hand, lacks these natural bacteria and healthy prebiotics.
- Stop using hand sanitizer and don’t be afraid to get dirty. We consume bacteria from our environment ALL THE TIME. Usually, we get a balanced dose of healthy (and not so healthy) bacteria, and our immune system & gut microbiota are able to fight off infection. But what happens when you disrupt this natural process and douse yourself in sanitizer or prevent your kids from getting down & dirty in nature? Well, you kill all the bacteria (good and bad) and prevent your body from being exposed to a healthy diverse range of bacteria. If your body never gets exposed to these healthy bacteria, it could over-react when it finally is exposed to them, and increase your risk of unnecessary immune responses (like in allergies and other autoimmune diseases like multiple sclerosis and type I diabetes). If you’re interested in learning more about this, check out the “hygiene hypothesis.” or, my favorite term, “microbial deprivation syndromes of affluence.”
So where is all this research headed?
Super interesting studies are being published as we speak, suggesting links between gut dysbiosis and obesity, type 1 diabetes, and even mental disorders like anxiety, depression, and autism, since a large portion of the peripheral nervous system is located in the gut. While this research is still new, it is certainly exciting.
Another hot topic right now? Fecal transplants. Yep. The transfer of fecal gut bacteria from one person to another. It is being investigated as a treatment for intestinal infections (like c. diff, which is common in hospitals and very tough to get rid of) & even as a treatment for obesity, since obese people have a less diverse microbiota with different proportions of bacteria than normal weight people.
Some animal studies have even suggested that fecal transplants can change the mood/behavior of the recipients to be more like that of the donor! Presumably this is because the fecal transplant changes the gut microbiota, which is closely connected to the brain and the rest of the central nervous system. This study found that fecal transplants from anxious mice to mice with sterile guts caused the inoculated mice to behave anxiously, like the mice from which they received the fecal transplant! This is some seriously amazing stuff!
Wow. How fascinating is your gut?
Hippocrates once said,
“All disease begins in the gut.”
While this is not entirely true, having a healthy microbiome clearly plays a large role in general wellbeing!