"All Disease Begins in the Gut" - Hippocrates
He was right thousands of years ago, and his wisdom carries over to today. The concept of "gut health" is nothing new, but thanks to an explosion of research backing its importance over the past decade, we're finally catching on to caring about it. We potentially have the power to mitigate a myriad of diseases by restoring a healthy flora, but understanding the mechanisms of the gut microbiome connectedness to disease and how to most effectively restore gut health is not fully understood. Much of what I share in this blog is supported by very strong bodies of evidence but due to the diversity of the microbiome, the individuals carrying around these trillions of little bacteria friends, and the variable environmental exposures, it's impossible to nail down a clear and linear explanation for how to perfect your own gut. But surely I will try :-)
The How (a brief explanation on how the gut microbiome works)
Prior to exiting the womb, humans have a completely sterile gut. Exposure to either bacteria in the birth canal or mother's skin (if delivered via cesarean) provides the first colonization of gut microbiome which will rapidly change over time with different exposures (breast milk, solid food, eating dirt..) and continues to change throughout a lifetime. The "ideal" neonate exposure is to have a natural vaginal delivery and to be breastfed for optimal gut microbial diversity (Cong et al, 2015) but long term implications for this are not clearly defined.
By the time we reach adulthood, our "body" is composed of 10x more bacterial cells than actual human cells! Let me repeat that- at a cellular level, we are composed of 10 times more of "germs" than we are of actual human. This is so freaky and so awesome. But this highlights a very intuitive idea-- we should really care about that which we're mostly made of.
There are several strains of not just bacteria but also viruses and fungus (i.e., candida) that when balanced by the composition of their counterparts, are essential for maintaining good health; it is when the balance is affected by the death of a certain bacterial colony that disease can occur. Clinically, it's easy to recognize what causes a dysregulation of our perfectly balanced gut. Antibiotics taken orally move through our digestive system, killing not just the "bad" bugs but also those that keep a true "infection" at bay. This is most obvious in a C. diff infection (a nasty cause of diarrhea that occurs usually after antibiotic use, when strains of bacteria that usually keep C. diff in check, allow it to overgrow and secrete a toxin causing disease.) Another commonly experienced example is women taking antibiotics for a urinary treat infection who then develop a yeast infection. The antibiotic surely did it's job, but maybe a little too well. How pleasant, right? Ugh.
The negative effects of using antibiotics doesn't stop there, however; their use has been implicated in other disease states such as obesity (Thuny et al) but with a less clear pathway. We know that antibiotic use reduces microbial diversity, but nailing down EXACTLY which strains are important has yet to occur. The point of this is not to deter you from using antibiotics! I am thrilled to live in an era where we treat previously life threatening disease with a simple 3-7 day course of an oral medication. This is to recommend the use ONLY when necessary, (i.e., don't ask your doctor for antibiotics when you have a cold or upper respiratory infection. Seriously. Your gut will thank you.)
Maybe the biggest regulator of our gut microbiome? Something for which we have complete control: DIET. In mice studies, switching from a plant based diet rich in prebiotics (fibrous food products that provide food for bacterium to feed) to a more "Western" diet rich in low-quality fats and high sugar content changed their gut bacterial composition within 1 day (Boathman et al.) We can discuss the actual disease implications of this later, but can we marvel at how powerful this is? What we consume/put into our bodies has the potential to change the composition of trillions of colonies within our intestines. Do you guys understand why I love the field of gastroenterology so much now? We really and truly are what we eat.
The Why (a short summary of why we should care about our gut health)
Doing a simple search of "microbiome and ____" on pubmed.gov will show something like this:
Clearly just by this screenshot, you can see the potential for implications of gut bacteria and an incredibly broad range of disease. This range is far from the standard deviations you'd expect (gut infections, nutrition related diseases) and extends to conditions such as Parkinson Disease, allergies, multiple sclerosis, and depression. Depression?! Related to the trillions of little germs in your gut? Just maybe. You'll notice that many diseases listed here are neurological, owing to the well developed understanding of the gut-brain axis. Our intestines have their very own complex nervous system, that is largely influenced by the microbiome. This is known as the ENS (enteric nervous system) and provides a 2-way road of feedback to our brains. Dysregulation of the microbiome can negatively affect basic functions of the gut (frequency of contractions/motility, gut hormone secretions) which in turn affects the signals up to the brain up top (Zhou et al.) Further, smaller interventioanl studies have emerged that suggest consumption of probiotics in humans may reduce anxiety and actually reduce measured cortisol levels (Messaoudi et al.) Now if that isn't the most fascinating thing you'll read today... :-P
I could go on with more studies showing support of microbiome's connection to ___ disease state, but I would literally be writing for days. I could go into more details on the intricate pathogenesis that supports these connections, but the truth is our understanding of it is still evolving. What I can assure you of is that gut health has the potential to affect possibly every aspect of our bodies and respective disease states, and the core of health and wellness is maintaining gut homeostasis. See what I mean about Hippocrates? He knew what's up.
The What (Simple suggestions on what we can do to obtain/maintain a healthy gut microbiome)
My first suggestion is to forget about what your gut's already been through-- you are not doomed if you were bottle fed or took too many antibiotics as a kid. Both of these examples happened to me (damn you, ear infections!) Your gut is not forever in despair if your current idea of "vegetables" is french fries dipped in ketchup (potatoes are basically a leafy green, right?) Additionally, you don't have to spend thousands of additional dollars onto your grocery bill to obtain a feeling of namaste in your gut.
The approach is simple. For optimal gut health, you should aim for a good balance of dietary components (fats, proteins and carbohydrates), and a proper consumption of probiotics and prebiotics (Targher et al, a great paper on the effects of gut microbiome and fatty liver disease.) The balance of dietary components will be different for everyone, and it's important to not generalize fat macronutrients, as poor-quality of fats such as trans fats and even processed vegetable oil fats likely have a different effect on our microbiome than naturally derived sources found in whole foods (avocados, coconuts, eggs, etc.) Avoiding high quantities of sugar is a MUST, as it promotes chronic low grade inflammation and ultimately disrupts gut homeostasis.
As a reminder, probiotics are the *actual* colonies of bacteria, often labeled as "live cultures" on things like yogurts, kombucha, fermented veggies, etc. To date, I am unaware of specific bacterial strains that are more crucial to consume compared to others (but when I know, you'll know!) I advise not worrying about these little details and just try to incorporate probiotics into your daily diet. The hygiene hypothesis by and large helped us live longer, but likely put us at risk for reduced microbial diversity and its consequences. Since we (luckily) live in a fairly sterile environment where are foods are not covered with dirt and potential risk for infectious disease, we lose out on naturally occurring consumption of microbial diversity. Equally important are prebiotics, undigested, fermentable fibers (Read: LOTS OF FRUITS AND VEGGIES) that feed the bacteria in your digestive system. If you're eating lots of food-based sources of probiotics/prebiotics you likely don't need to take an actual supplement. It wouldn't hurt to take one, but I'd save a buck and just focus on a well balanced diet with lots of plants.
As we move forward in disease management, you might notice the use of fecal microbiotia transplant for many conditions. Yes, transplant. Meaning taking someone else's healthy poop and transplanting it into a sick person's digestive system! (I know, I know, it's the coolest thing in medicine.. and yes, I really want to be a donor.) This is already FDA approved for severe C. diff infections and is soon to have accepted indications for treating conditions such as inflammatory bowel disease, hepatic encaphalopathy (the condition of confusion or even coma due to high levels of toxic chemicals that can't be excreted due to liver failure), type II diabetes, obesity, and the list goes on. I'm not saying to get yourself a fecal transplant, I'm just saying.. get you a gut that's so healthy you could be a donor ;-)
Conclusions? Gut health is really, REALLY important in reducing/altering disease throughout our entire body. Despite our microbiomes having aspects we can't change such as genetic factors, improving our guts is simple: eat a wide variety of mostly whole foods and LOTS of plants, and consume probiotics in your favorite form (ahem, *kombucha.*)
I know this was a lot of content- PLEASE let me know if you have any questions. If i didn't talk about it here, I've probably read about it! This is, after all, one of my favorite topics in medicine! Happy Guts for you all!!