Understanding Leaky Gut…and What Causes It (Part One of Three)
Something I’ve noticed is that there are a surprising number of topics that I have not covered on the blog…even though they are part of my daily work! Leaky gut is one of them. In fact, when I got writing, the post ballooned to the point where I realized I had to break it into multiple parts. Over the next week, I’ll drop three articles encompassing a ‘basic’ primer on leaky gut to help you separate fact from internet fiction.
The article is referenced, click the links on the reference numbers. And yes, the number order is wonky because of how I kept expanding the article!
The term ‘leaky gut’ sounds so much like internet wellness garbage that it can be easy to dismiss it outright. In fact, a lot of professionals do – which would be a mistake.
Known in the scientific literature as gut barrier dysfunction, leaky gut is exactly like it sounds: the gut barrier itself is not working properly. And yes, I know this explanation doesn’t really sound so self-explanatory. Let’s start at the beginning with a bit of anatomy and physiology.
Your Gut: The Final Frontier
Your gut is one long muscular tube that is continuous with the outside world, from your mouth on down to the poop shoot – and yes, I know how gross that sounds to link the two but they are in fact linked and it’s important.
Even though you think of your gut as being inside of your body, technically it is the outside world. And the outside world is a scary place: microbes, toxins and unfamiliar stuff that might mess you up. So your gut is actually a defensible border, just like your skin is. However, unlike your skin, your life depends on being able to absorb a lot of good stuff (like water and proteins and vitamins) through your gut, resulting in a barrier that is a lot more fragile, dynamic and porous than your relatively thick skin.
If your gut were simply a digestion machine, this may not be a significant finding. However, your gut lies at the intersection between digestive, immune and neurological health. The vast majority of your immune activity is centred along and within the gut. Your gut has more nerve cells than your spinal cord. Oh, and there are trillions of bacteria hanging out in there too.
More Than a Wall: Understanding the Gut Barrier
The gut barrier is a tightly regulated frontier that requires precise cooperation between all three systems in order to function properly1,5. The razor’s edge between inside and outside is a single cell-thick layer of absorptive gut cells. These gut cells are linked together at areas called tight junctions. These tight junctions ensure that substances pass only through regulated transporters on the gut cell surface, instead of slipping in between the cells like a bandit at midnight. It is worth noting that only very small molecules can pass through by normal means. Which is why your body breaks down proteins into their amino acid building blocks – a whole protein molecule cannot pass the digestive gates, which is lucky because proteins from the outside world are good at causing immune reactions. Same thing with bacteria: if the gut barrier is working well, bacteria stay in the gut and cannot enter your system.
On top of that layer of gut cells, you should also have a thick layer of mucus that acts as another layer of protection against the outside world. It is denser near the gut cell and relatively microbe free, and looser toward the space of the gut where it houses a bunch of microbes all cozy in the goop3,5. Now, I know you’re gonna see that word mucus and think it’s a bad thing and that you should all go and get a colonic. Don’t. That mucus is 100% critical to gut barrier integrity and without it, there’s real trouble. In addition to physical protection, the mucus also contains antimicrobials that control the bacterial population and limit its access to the gut cell3. If the mucus layer thins, bacteria are going to gain direct access to the gut cell and there is going to be inflammatory trouble3.
Your body is remarkably intelligent: its symbiotic relationship with your gut bacteria has resulted in a complex dance of physiology and immunity that both welcomes beneficial microbes and ensures they know their place. Depending on which part of the gut you’re in, the defense structures look different. Your gut barrier is tighter and stronger in the colon than the small intestine4, which makes sense; you are absorbing most of your nutrients in the small intestine and there are WAY more bacteria in the colon. We’re talking millions or maybe billions in the small intestine to compared to trillions in the colon.
What causes leaky gut?
Any inflammatory response is thought to cause increased gut permeability at least temporarily4. Leaky gut is another feature of disease states that have recognized impacts in clinical medicine but have been met with skepticism in a subacute or chronic form. For example, gut barrier dysfunction is known to exist in liver disease, diabetes, inflammatory bowel disease, celiac disease and traumatic burn injuries.
So if you’re walking around looking pretty good and saying you have leaky gut, you can imagine the source of the skepticism. However, I am fairly confident based on the progression of the scientific literature that this won’t be the case for long, as we have seen with chronic stress and chronic inflammation.
What started to move the conversation forward was the discovery of zonulin, a molecule that can zip open the tight junctions like a zipper. The research on zonulin release in celiac disease in response to gluten ingestion has laid a lot of ground work for understanding the interactions between the gut, the immune system, gut bacteria and immuno-active components of food. If something causes the tight junction to falter, large molecules presented to the immune system can trigger reactions with far-reaching outcomes the longer they continue.
You cannot fully tell the gut barrier story without talking about the gut microbes it protects you from. Germ-free studies have shown us that without gut microbes, the gut barrier doesn’t develop or function properly; on the flip side, if your gut flora is imbalanced or pro-inflammatory, you’re also screwed1,5. Gut microbes have been shown to influence the actions of zonulin in addition to their influence on inflammatory response5.
Feed Your Gut Barrier
Diet is a biggie: it is thought that a chronic absence of fibre kills off the beneficial gut bacteria that feed on it. This imbalance may favour the overgrowth of gut bacteria that survive by literally eating the mucus layer of the gut, degrading the gut barrier3. Some fibre-loving bacteria also produce butyrate, a short chain fatty acid that feeds the gut cell and supports the integrity of the gut barrier4.
High fat, high sugar diets – along with alcohol ingestion – are known to alter the gut barrier4. One contributing factor may be that high fat diet alters the pool of bile acids in the gut which can alter zonulin release and lead to gut barrier dysfunction by non-inflammatory means2.
There is still so much to learn about the underlying causes of gut barrier dysfunction but without a doubt we are looking at a complex interaction of genetics, lifestyle and environment. Celiac disease is a great example of this, where those with the genetics may not get the disease; it takes an environmental trigger and then the ingestion of gluten to start breaking down the gut. And the gut barrier may hold links to the brain barrier too; for example, those with genetic susceptibility to schizophrenia show alterations in genes that also involve gut barrier6.
Still with me? Stay tuned for parts two and three, where I will cover the impact of leaky gut, testing and potential options for getting better.
Photo Credit: Alison Marras on Unsplash