Digestive tract - by Doug Cook RD

Leaky Gut, Autoimmunity & Mental Health. What’s The Link? Part 1


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The gut (a.k.a. digestive tract) is not just a tube that absorbs nutrients and gets rid of waste – it’s a complex alive system and is one of the foundational aspects of health, and not just gut health, but the overall health of our bodies and minds. We know how important it is to get the 50+ essential nutrients we need from food – and this is a big part of what our digestive tract does. But, there is far more to the story than just that.


When the gut is not working properly, symptoms can appear. Yes, typical gut and abdominal symptoms like gas, bloating, and cramps, but also other seemingly unrelated symptoms. Did you know that things like allergies, autoimmunity, skin issues, and mental health have been linked with gut problems?


Looking at one gut problem in particular (you may have heard about this lately) – leaky gut. This literally involves tiny “leaks” in our gut lining that can allow more than just needed nutrients and water into our bodies. Researchers have been looking into this for decades but more conservative folks prefer to use one of several preferred terms such as gut barrier dysfunction, increased intestinal permeability, mucosal barrier dysfunction to name a few but make no mistake, leaky gut is no fringe concept. In this post I wanted to give you some of the latest on this hot topic, as well as, helpful strategies to optimize your gut health, to improve your overall health!


What is “leaky gut” linked with?


The “gut” is part of the digestive system, mainly the intestines, which are located in the abdomen. It’s an alive, active, dynamic and very complex “tube” that acts as a gateway deciding what will enter the internal circulation of the body, and what must not get by its protective barrier. It digests and absorbs nutrients and water. It prevents toxins, excessive amounts of food proteins (a.k.a. antigens) and “bad” microbes (bacteria) and their toxins from being absorbed, all the while shuttling waste on its journey to ultimately be eliminated.


You may think that symptoms of a leaky gut (a.k.a. “increased intestinal permeability”) are felt in the gut, and you’re right…to a point, but would you be surprised to know that lots of other symptoms and conditions that are not located just to the gut are linked with leaky gut as well?


Leaky gut has been associated with:


  • Autoimmune diseases (e.g. Type I diabetes, celiac disease, rheumatoid arthritis, lupus etc.)
  • Inflammatory Bowel Disease (e.g. ulcerative colitis, Crohn’s)
  • Psychological stress and mental health, mood disorders
  • And more!


Researchers are still figuring out the exact role that leaky gut plays in these conditions. Either way, the connections are there, and there are things that you can definitely do to improve your gut health. But first, how is our gut structured, and what can promote it to leak and impair its role as a protective & selective barrier?


Gut structure – Three layers of our gut lining


Our guts have a three-layer lining that helps to allow things we need in, and keep harmful things out.


The first (outermost) layer is just one-cell thick. It’s a barrier that absorbs the nutrients and water we need, and physically prevents undigested compounds, toxins, and bacteria from getting in. Laid out flat, this layer makes up the largest surface area between the internal circulation of our bodies and the outside world (i.e. what we eat and drink).


This layer has at least seven different types of cells, and 90% of them are one type called “enterocytes.” These enterocytes actively absorb what we need and keep out what we don’t. They also help to create and regulate the other two layers.


FUN FACT: Most enterocytes are replaced with new ones every 3-5 days or so. INCREDIBLE


Enterocytes are held together with different types of bonds. The one most studied is called a “tight junction.” These tight junctions are made up of several types of protein. When they loosen, it creates tiny openings (or permeations) in this first layer since the cells are not “stuck” together as much as they should be. Think of it like someone leaving the gate open and something unwanted getting into your yard.

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The second layer is mucus. This mucus provides physical separation between the outermost enterocyte layer and the microbes and food that are inside the centre, or “lumen,” of the gut. It also contains special proteins that help fight against invaders. This mucus and its special compounds are produced by the enterocytes.


We want that mucus layer to be nice and thick to provide a better barrier between the one-cell layer of enterocytes and protect them from “bad” bacteria that can get in there.


FUN FACT:  Animal studies show that mice fed a diet low in fibre had thinner mucus barriers.


The third (innermost) layer inside our gut lining is our friendly resident gut microbes. Our guts contain billions of microbes – over 1 kg worth. Taken together, they’re sometimes referred to as a “superorganism.” These microbes include bacteria as well as other types of friendly microbes.


This layer of gut microbiota has two major functions to help promote a healthy gut lining:


  • They crowd out “bad” bacteria by taking up space and eating the “good” food (i.e. fibre and resistant starch that helps them grow and populate the digestive tract, we’ll get into this more in a bit).
  • They also help to regulate the digestion and absorption of nutrients to nourish the digestive tract’s first-layer of cells, the enterocytes. One of the types of compounds they produce are called “short chain fatty acids” (SCFAs). These are considered to be anti-inflammatory and are also used as fuel for the enterocytes.


When the three layers aren’t working optimally, the tight junctions loosen, and leaks occur. This allows unwanted things to enter into the body’s circulation. This is how the health of our gut health affects our overall health.


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Leaky gut and our gut microbes


Our friendly gut microbes, the third innermost layer of our gut, include hundreds of types of microbes. Some of the main types of bacteria are Bacteroidetes and Firmicutes (e.g. Lactobacillus). A bulk of the evidence points to the idea that problems (imbalances etc.) with our gut microbes might actually start the whole process of leaky gut/gut barrier dysfunction.


According to Sturgeon and Fasano, 2016:


“It is now clear there is a symbiotic relationship between the microbiome and the host. As early as 2001, it was described that commensal bacteria have an effect on intestinal permeability.” [Commensal refers to a biological relationship between two species where one, us humans, gain benefits from another, our bacteria].

Gut bacteria 300x300 - Leaky Gut, Autoimmunity & Mental Health. What's The Link? Part 1Here’s how we think this happens, based on the current research:


  • The third innermost layer of the gut lining, the microbiota, get out of balance.
  • Inflammatory molecules (including zonulin) are released, and fewer anti-inflammatory ones like SCFAs are available.
  • This inflammation disturbs the tight junctions in first layer of enterocytes, hence creating tiny leaks/openings which allows passage of harmful compounds (bacteria, bacterial toxins, food proteins) into our bodies.


It starts when the gut microbiota are in dysbiosis (an “imbalance” of “good” and “bad” microbes). This promotes an inflammatory response because some of the “bad” microbes are pushing out the “good” ones that produce the anti-inflammatory short chain fatty acids (SCFAs). SCFAs are anti-inflammatory and are also used as fuel by the enterocytes. Some of these SCFAs promote the production of the mucus layer (the second layer), and even help to improve the tight junctions in the enterocytes in the first layer. They produce the SCFAs when they eat fibre and resistant starch.


FUN FACT: One study looked at children who were at risk of developing type 1 diabetes (which is an autoimmune condition). Researchers found that some who had an increase in one of the “bad” microbes went on to develop autoimmunity months later which led to type 1 diabetes.


Another possibility that researchers are looking at is that some of these “bad” bacteria produce a toxin that mimics zonulin.


Zonulin is a protein naturally released by our enterocytes when they’re exposed to certain things we eat, like “bad” bacteria on our food and gliadin (part of the gluten protein found in wheat and other grains). Blood levels of zonulin tend to be higher in people with autoimmune conditions like celiac disease and type 1 diabetes and those with elevateg IgG antibodies (associated with food sensitivities).


All of this increased inflammation then irritates the gut, which can result in loosening of those tight junctions which is like opening the gates to the yard and letting things enter in an uncontrolled way. When this happens, the immune system is kicked into action. Based on the research so far, this is the way we think we develop leaky guts. But, how does this relate to autoimmunity? I’ll answer that in Part 2 of this post


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Doug Cook RDN is a Toronto based integrative and functional nutritionist and dietitian with a focus on digestive, gut, and mental health.  Follow me on Facebook, Instagram and Twitter.