What is leaky gut?
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 that’s a huge foundation of health. And not just gut health, but the overall health of our bodies and minds. We know how important it is to get all of our essential nutrients from food - and this is a big part of what our digestive tract does. But, there is way more to the story than just that.
When the gut is not working properly, symptoms can appear. Yes, typical gut and abdominal symptoms, but also other seemingly unrelated symptoms. Did you know that things like allergies, autoimmunity, and mental health have been linked with gut problems?
Let’s look 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 are looking at this, and I want to share the latest with you, as well as give you some helpful strategies to optimize your gut health, for 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 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. It digest and absorbs nutrients and water. It prevents toxins and “bad” microbes from being absorbed. And it shuttles all the waste to continue on and be eliminated.
You may think that symptoms of a leaky gut (a.k.a. “intestinal permeability”) are felt in the gut, and you’re right...to a point. Would you be surprised to know that lots of other symptoms and conditions are linked with leaky gut?
Leaky gut has been associated with:
● Autoimmune diseases (e.g. Type I diabetes, celiac disease, etc.)
● Inflammatory Bowel Diseases (e.g. ulcerative colitis, Crohn’s)
● Psychological stress and mental health
● 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. Let’s look at how our gut is structured, and what can promote it to leak?
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.
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 holes (or permeations) in this first layer since the cells are not “stuck” together as much as they should be.
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, which we’ll get into in a bit).
● They help to regulate the digestion and absorption of nutrients to nourish the first-layer 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 gut health affects our overall health.
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). We think problems with our gut microbes might actually begin the whole process of leaking guts.
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.”
Here’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 which allows passage of harmful compounds 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.
All of this increased inflammation then irritates the gut, which can result in loosening of those tight junctions.
Based on the research so far, this is the way we think we develop leaky guts.
Leaky gut, or “intestinal permeability” is linked with many conditions of the gut, the body, and the mind. While research is still figuring out exactly how this happens and what comes first, there are definitely steps you can take today to help optimize your health. Learn how you can promote a healthy gut here!
Aguayo-Patrón, S. V., & Calderón de la Barca, A. M. (2017). Old Fashioned vs. Ultra-Processed-Based Current Diets: Possible Implication in the Increased Susceptibility to Type 1 Diabetes and Celiac Disease in Childhood. Foods, 6(11), 100. http://doi.org/10.3390/foods6110100
Brzozowski, B., Mazur-Bialy, A., Pajdo, R., Kwiecien, S., Bilski, J., Zwolinska-Wcislo, M., … Brzozowski, T. (2016). Mechanisms by which Stress Affects the Experimental and Clinical Inflammatory Bowel Disease (IBD): Role of Brain-Gut Axis. Current Neuropharmacology, 14(8), 892–900. http://doi.org/10.2174/1570159X14666160404124127
Fasano A. (2011). Zonulin and its regulation of intestinal barrier function: the biological door to inflammation, autoimmunity, and cancer. Physiol Rev. 91(1):151-75. doi: 10.1152/physrev.00003.2008.
Holtmann G, Shah A, Morrison M. (2017). Pathophysiology of Functional Gastrointestinal Disorders: A Holistic Overview. Dig Dis, 35 Suppl 1:5-13. doi: 10.1159/000485409.
Holzer, P., Farzi, A., Hassan, A. M., Zenz, G., Jačan, A., & Reichmann, F. (2017). Visceral Inflammation and Immune Activation Stress the Brain. Frontiers in Immunology, 8, 1613. http://doi.org/10.3389/fimmu.2017.01613
Kelly, J. R., Kennedy, P. J., Cryan, J. F., Dinan, T. G., Clarke, G., & Hyland, N. P. (2015). Breaking down the barriers: the gut microbiome, intestinal permeability and stress-related psychiatric disorders. Frontiers in Cellular Neuroscience, 9, 392. http://doi.org/10.3389/fncel.2015.00392
Lamprecht, M., Bogner, S., Schippinger, G., Steinbauer, K., Fankhauser, F., Hallstroem, S., … Greilberger, J. F. (2012). Probiotic supplementation affects markers of intestinal barrier, oxidation, and inflammation in trained men; a randomized, double-blinded, placebo-controlled trial. Journal of the International Society of Sports Nutrition, 9, 45. http://doi.org/10.1186/1550-2783-9-45
Lerner, A & Matthias, T. (2015). Changes in intestinal tight junction permeability associated with industrial food additives explain the rising incidence of autoimmune disease. Autoimmun Rev, 14(6):479-89. doi: 10.1016/j.autrev.2015.01.009.
Lerner, A., Neidhöfer, S., & Matthias, T. (2017). The Gut Microbiome Feelings of the Brain: A Perspective for Non-Microbiologists. Microorganisms, 5(4), 66. http://doi.org/10.3390/microorganisms5040066
Mu, Q., Kirby, J., Reilly, C. M., & Luo, X. M. (2017). Leaky Gut As a Danger Signal for Autoimmune Diseases. Frontiers in Immunology, 8, 598. http://doi.org/10.3389/fimmu.2017.00598
Slyepchenko, A., Maes, M., Jacka, F.N., Köhler, C.A., Barichello, T., McIntyre, R.S., Berk, M., Grande, I., Foster, J.A., Vieta, E. & Carvalho, A.F. (2017). Gut Microbiota, Bacterial Translocation, and Interactions with Diet: Pathophysiological Links between Major Depressive Disorder and Non-Communicable Medical Comorbidities. Psychother Psychosom, 86(1):31-46.
Sturgeon, C., & Fasano, A. (2016). Zonulin, a regulator of epithelial and endothelial barrier functions, and its involvement in chronic inflammatory diseases. Tissue Barriers, 4(4), e1251384. http://doi.org/10.1080/21688370.2016.1251384
Wikipedia. Bacteroidetes. Accessed May 22, 2018.
Wikipedia. Firmicutes. Accessed May 22, 2018.
Wilms, E., Gerritsen, J., Smidt, H., Besseling-van der Vaart, I., Rijkers, G. T., Garcia Fuentes, A. R., … Troost, F. J. (2016). Effects of Supplementation of the Synbiotic Ecologic® 825/FOS P6 on Intestinal Barrier Function in Healthy Humans: A Randomized Controlled Trial. PLoS ONE, 11(12), e0167775. http://doi.org/10.1371/journal.pone.0167775
World Health Organization, Food and Agriculture Organization. Probiotics. Accessed May 22, 2018.
Xiao, L., van’t Land, B., van de Worp, W. R. P. H., Stahl, B., Folkerts, G., & Garssen, J. (2017). Early-Life Nutritional Factors and Mucosal Immunity in the Development of Autoimmune Diabetes. Frontiers in Immunology, 8, 1219. http://doi.org/10.3389/fimmu.2017.01219