Imagine source: Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. - Own work
“Leaky gut,” more accurately known as intestinal hyper-permeability, is one of the drivers of many health conditions and disease processes. While certainly not complete, our understanding of this condition has been growing over the past several decades. So, what is leaky gut and why should you care about it? In this article you’ll learn why the anatomy and function of the gut lining are so important, some of the various influences that can make the gut “leaky,” and symptoms/diseases associated with leaky gut.
First, A Little Anatomy
Imagine source: https://thoracickey.com/small-intestine/
The “gut” is essentially a long, twisting, hollow tube of varying widths that starts at the mouth, ends at the anus, and in between is comprised of the esophagus, stomach, small intestine, and large intestine. This hollow space (aka “lumen”) of the gastrointestinal (GI) tract is technically outside of the body. For something to get from the GI tract into the body, it needs to cross the physical barrier of these structures. Once something crosses over from the lumen of the GI tract to the body, it has access to the bloodstream where it can then travel around.
When we talk about leaky gut, we’re mostly talking about the small intestine. The wall of the small intestine is comprised of four layers, one of which is the mucosa. The mucosa is the layer facing the inside of the gut lumen and is also made up of sublayers which include the muscularis mucosae, lamina propria, and a layer of epithelial cells. It is this layer of epithelial cells that creates the physical barrier between you and the outside world. The lamina propria provides a more functional role by housing the majority of our immune system.
The mucosa has a wave like shape (see image). The wavy, finger-like projections that line the small intestine are called villi. The epithelial cell layer lines the villi and serves as the physical barrier between the hollow space of your gut and the inside of your body. As you can see in the image, this layer of cells is only one cell thick. Once something crosses this single layer of cells, it has access to the bloodstream (depicted as red wavy lines) and can trigger the immune system. The epithelial cells are held together by what are called tight junctions and are lined with even smaller finger-like projections called microvilli.
How Does The Gut Lining Benefit Me?
The abundance of villi and microvilli lining the small intestine help to increase surface area in the gut to allow more opportunity for nutrient absorption. The intestinal mucosa serves the seemingly opposing roles of remaining closed enough to protect us from the outside environment while also opening enough to absorb needed fluids and nutrients (Bischoff et al., 2014). It is not a stagnant barrier, but rather dynamically adapts to fulfill both of these roles. By remaining closed enough, the mucosa helps instill a sense of peace in the body by keeping potentially harmful “foreign invaders” out of the bloodstream and also allows a space for our highly important microbiome to live without causing immune disturbance (Bischoff et al., 2014). On the other hand, having such a concentrated amount of immune tissue, the mucosa is also always at the ready to initiate the inflammatory process to fight invading pathogens and other harmful substances. The tight junctions, and the cells lining the villi themselves, help regulate what can pass from the gut lumen into the bloodstream. In a perfect world, we’d have healthy villi and microvilli for optimal nutrient absorption and we’d have well-regulated tight junctions to allow nutrients in but keep undesirable compounds out.
In the real world, however, this delicate lining of the small intestine is susceptible to damage. The microvilli and villi can become “blunted,” decreasing in height and thereby reducing the surface area available for nutrient absorption, potentially leading to nutrient deficiencies or malabsorption. The tight junctions and epithelial cells can also lose integrity and malfunction. When the lining of the small intestine is damaged, it can no longer discriminate as well regarding what can cross from the gut lumen into the body, leading to increased influx of intestinal contents both between and through the cells. This allows compounds that should not be circulating around the body access to the bloodstream to do just that.
What Can Damage The Gut Lining?
Intestinal hyper-permeability can come on suddenly or gradually over time (Bischoff et al., 2014). Some of the contributing factors that can lead to increased intestinal permeability include:
Antibiotics and antacids (Yoon et al., 2018)
NSAIDs (aspirin, ibuprofen, etc.) (Yoshikawa et al., 2017)
Infections (Dagci et al., 2002)
Dysbiosis (Morris et al., 2016)
Stress (Punder & Pruimboom, 2015)
Synthetic chemicals/toxins (Gillois, Lévêque, Théodorou, Robert, & Mercier-Bonin, 2018)
Food additives (Lerner & Matthias, 2015)
Gluten (Hollon et al., 2015; Punder & Pruimboom, 2015)
Alcohol (Patel et al., 2015)
Celiac disease and non-celiac gluten sensitivity (Parzanese et al., 2017; Hollon et al., 2015; Uhde et al., 2016)
A Western Standard American Diet (Bischoff et al., 2014)
Nutrient deficiencies such as vitamin A and vitamin D (Bischoff et al., 2014)
So What? Why Does It Matter If My Gut Is Leaky?
Your immune system is trained to distinguish between your tissues and what is beneficial for the body such as vitamins and minerals versus what is potentially harmful for your body such as certain bacteria, viruses, and synthetic chemicals. When the gut is hyper-permeable, it more readily allows these undesirable compounds to enter the bloodstream. This alerts the immune system that there is a “foreign invader” and action is required. When the immune system kicks into gear, it creates inflammation. Inflammation is thought to be one of the drivers behind most disease processes, including chronic, non-communicable diseases (Hunter, 2012; Punder & Pruimboom, 2015). Having a good, robust gut lining ensures that the foreign invaders stay out of your body to keep the immune system from going on high alert. Here is a list of just some of the conditions associated with inflammation:
Cardiovascular disease
Diabetes and blood sugar dysregulation
Alzheimer’s disease and dementia
Parkinson’s disease
Cancer
Arthritis
Generalized pain
Other metabolic conditions like non-alcoholic fatty liver disease
Obesity
Asthma
Autoimmunity
Skin rashes such as eczema and psoriasis
Chronic fatigue
As you can see, dysfunction that starts in the gut doesn’t necessarily stay in the gut due to the potential for system wide inflammation when leaky gut is present. One molecule that gets attention for contributing to systemic inflammation in the presence of leaky gut is lipopolysaccharide, or LPS for short. LPS is an endotoxin attached to the outer membrane of certain types of bacteria. We evolved to live symbiotically with bacteria and other organisms known as the microbiome. While the microbiome provides numerous positive functions and even helps protect against leaky gut, it can also release toxic byproducts. The body has devised ways to cope with these toxic byproducts so that we can live in harmony with and derive the benefits from our microbiome while at the same time protecting our interior cells, tissues, and organs from the inflammatory process (Wassenaar & Zimmermann, 2018). The intestinal lining is one such way our bodies are able to maintain a symbiotic relationship with the microbiome by keeping it in the gut lumen. When the intestinal lining breaks down, LPS can leak out into the bloodstream where it can damage cells and contribute to conditions such as diabetes, cardiovascular disease, Alzheimer’s disease, and autism (Ahola et al., 2017; Punder & Pruimboom, 2015)
Given the wide array of health conditions that can be fueled by a dysfunctional gut barrier, making an effort to protect and nourish the gut is a worthwhile endeavor. While the various factors that contribute to leaky gut will be different in each person, basic diet and lifestyle practices like eating a colorful, fiber-rich, whole foods diet; avoiding synthetic chemicals in food, body care products, and cleaning products; managing stress; getting adequate sleep and exercise; and minimizing antibiotics and NSAID use as much as possible are all good places to start.
REFERENCES
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