There is one piece of gut trivia I share with patients that consistently causes their jaws to drop: everything inside of your gut is actually outside of your body. Take a few seconds to let that sink in. It’s weird, right?
Your digestive tract (a.k.a. the gut, gastrointestinal tract, GI, etc.) is actually one long tube from your mouth to your anus and the cells lining it separate the inside (which is you!) from the outside (which is the contents of your gut including a whole world of microbes).
The first time I heard this idea was in Naturopathic Medical School. I was so fascinated by it and immediately knew it was more than a piece of trivia; it had great significance. Now that you understand that the contents of your gut are outside of your body, we are in a good place to start talking about the infamous leaky gut, how it impacts health and disease, and the science behind it.
The Anatomy & Physiology of a Healthy Gut
Let’s start first with learning a little bit more about the structure and function of a normally functioning gut. As noted above, your digestive tract includes every part of the tube between your mouth and anus; it also includes accessory organs like your salivary glands, liver, gallbladder, and pancreas. For the purposes of understanding leaky gut, we will be mainly concerned with the small and large intestines (the large intestines are also known as the colon).
There is a thin layer of cells, called the intestinal epithelium, that lines the inside of the small and large intestines. The intestinal epithelium is only one cell thick and this is the barrier between you and the outside world of inside your gut! There are six different types of cells in this part of your GI tract. Each cell type has a different specialty:
- Nutrient breakdown
- Nutrient absorption
- Mucus production
- Gut hormone production
Regardless of their specialized function, these cells should spend most of their time sitting very close to each other in order to make sure the barrier between inside and outside is very tight. This allows them to be discriminatory in regards to what gets into your body. In fact, one of the anatomical structures that holds the gut cells together is called a tight junction.
What’s a Leaky Gut?
Nutrients (such as vitamins, minerals, proteins, etc.), viruses, bacteria, and other pathogens can get into your body in two ways: enterocytes (the gut cells that specialize in nutrient breakdown and absorption) can choose to bring substances across the barrier through a transport system embedded in them or substances can cross when the cells lining your gut are no longer fitting snug up against each other. In the later scenario your body doesn’t get to discriminate between things that are good for you and things that are bad for you. You want to bring nutrients into your body but you do not want to allow pathogens including viruses and certain bacteria into your body.
When your gut cells no longer fit tightly together and function as a discriminating barrier, this is when you have what is called a leaky gut. This can happen temporarily as a normal physiologic function, it doesn’t contribute to overall poor health, and it is often referred to as intestinal permeability, especially in scientific literature. However, when intestinal permeability happens for prolonged periods of time and is accompanied by inflammation, this is what is often referred to as leaky gut. Prolonged intestinal permeability can have very big repercussions on your health, including your gut and even more.
Some skeptics are still saying that there is no such thing as leaky gut; however, it is a simple physiologic fact that it does occur. Mainstream sources such as WebMD are beginning to recognize its existence and many recent studies and reviews (1, 2, 3) are giving us more information about why it happens, impacts on health, and what can be done about it.
Why Should We Care about Leaky Gut?
- Non-Alcoholic Hepatosteatosis (NASH)
- Parkinson’s disease
- Autoimmune disease
- Irritable Bowel Disease (IBD) – including Colitis, Crohn’s disease
- Graves’ disease
- Rheumatoid Arthritis
- Ankylosing Spondylitis
- Multiple Sclerosis
- Type 1 diabetes
- Irritable Bowel Syndrome (IBS)
- Atopic dermatitis
The Link Between Leaky Gut & the Immune System
It is a little mind blowing that the health of one thin layer of cells can contribute to so many greater health issues. You are probably wondering how this is possible. One explanation has to do with another amazing piece of gut trivia: your gut contains about 80% of your immune system. This part of your immune system lives in the mucosa (tissue) below that thin barrier of cells. This mucosa has a special name: GALT or gut associated lymphatic tissue.
When the gut becomes leaky, the immune system gets exposed to many things that it should not be. An immune response to the contents of the gut including normal gut flora and food is the result. This creates inflammation and sometimes an autoimmune reaction. The inflammation occurring in the gut will impact absorption of nutrients and also impact the health of the gut microbiota. (Gut microbiota is the formal term now used to described the complex community of organisms found in the gut of all animals.) These two things in turn will impact your overall health (9, 10). A second explanation is that the leaky gut allows larger than normal particles to cross across the barrier and, not only cause local issues with the GALT, but cause more direct systemic issues, such as the those listed above.