What Is Leaky Gut?

Middle aged woman sitting on bed, putting hands on belly, suffering from stomach ache. The term “leaky gut” describes the phenomenon, and the aftermath, of having an intestinal barrier that is more permeable than normal. The “than normal” is important here. Your gut is designed to be selectively permeable. Nutrients, electrolytes, and fluids need to be able to move in and out as part of normal, healthy digestion. Meanwhile, all the potentially dangerous stuff—pathogens, toxins, undigested food that shouldn’t be absorbed into the body—is meant to stay put and continue its journey down the digestive tract.  

Regulating gut permeability is no small task. In most popular conceptions of human physiology, the gut exists primarily as a passive conduit along which food travels. But it’s much more complex than that. The walls of your intestines are a dynamic boundary between you and the external world. The intestinal barrier is made up of layers of mucus, epithelial cells, muscle, and immune system components. When working as intended, the barrier allows the gut to safely house the microbes that reside there, judiciously lets good things into the body, and keeps harmful things out. 

Sometimes, though, the system starts to break down. The metaphorical doormen that are supposed to let only certain people into the club go to sleep on the job. Undesirables starts sneaking in. Sometimes the doors are flung open wide, and all the riffraff get through. When that happens, all hell breaks loose. The result is chronic inflammation, autoimmune illness, allergies, and more.

Most people are probably walking around with some degree of leaky gut thanks to the unhealthy lifestyle practices and environmental exposures that are unavoidable nowadays. Here’s what you need to know.

What is Leaky Gut?

Lining the gut are epithelial cells whose cell membranes fuse together to form protein complexes called tight junctions. Those tight junctions can open up. When that happens, toxins, harmful microbes, and partially digested food particles can escape the gut and make their way into the bloodstream, leading to infection, chronic inflammation, and the sustained immune response that characterizes autoimmune illness. 

As we learn more and more about gut health and the microbiome, it is evident that high intestinal permeability is a hallmark of just about every autoimmune and chronic metabolic disease. Just as a sampling, leaky gut has been associated with

  •  Celiac disease
  • Symptoms of poor digestion, like bloating, gas, or constipation
  • Inflammatory bowel disease (IBD)
  • Irritable bowel syndrome (IBS)
  • Asthma
  • Autism
  • ADHD
  • Food allergies and intolerances
  • Rheumatoid arthritis
  • Eczema
  • Depression, anxiety
  • Obesity and metabolic syndrome
  • Diabetes, both type 1 and type 2
  • Multiple sclerosis

While there is some debate about which comes first, the hyperpermeability or the disease, we know that in many cases, increased gut leakiness precedes, and may even be a necessary precursor for, disease onset.1 2 Once the disease process is set into motion, the chronic inflammation that accompanies all these disease states can further impair gut health, leading to a downward spiral.

What Causes a Leaky Gut in the First Place?

As I’ve discussed previously, gut health depends on having a healthy robust microbiome. We need the right balance of different commensal (helpful) microbes, and we need them to flourish in the right parts of the gut. These microbes, mostly bacteria, aid in digestion, hormone production, and immune system function. They also play a crucial role in maintaining the integrity of the gut lining. And importantly, they keep the bad guys in check, preventing the proliferation of harmful species. Leaky gut seems to result from a disruption of this delicate balance, which is related to—either as a cause or consequence of—inflammation in the gut.3 Anything that interferes with the composition of the microbiome or that leads to inflammation in the gut could increase permeability. 

Diet is, of course, one of the biggest levers we can pull when it comes to gut health, and I’d nominate gluten as public enemy number one here. When gluten is broken up into fragments in the gut, those fragments induce the release of zonulin, which tells the tight junctions to become more permeable.4 This happens to everyone whose guts come into contact with those gluten fragments, but the effect is enhanced in people with celiac. 

Other things that can increase intestinal permeability are

  • Pathogenic infection 5 6
  • NSAIDs
  • Excessive alcohol consumption
  • Smoking7
  • Radiation therapy or chemotherapy
  • Exposure to environmental toxins like lead 8 and cadmium 9

 And let’s not forget the big lifestyle factors: chronic stress, too little sleep, and low vitamin D thanks to insufficient sun exposure.10 Basically, stray too far from the 10 Primal Blueprint Laws, and gut health inevitably suffers. 

How to Test for Leaky Gut

Everyone’s gut is a little leaky, but if you have any of the health conditions listed above, it’s a safe bet that your gut is leakier than you’d like.  

The symptoms of leaky gut tend to be non-specific, ranging from skin issues to headaches to brain fog. Leaky gut probably isn’t the first thing your doctor will test for, especially not an allopathic physician, but it’s worth checking out if you can’t get to the root of your issues. A simple blood test can look for elevated zonulin,11 a protein that is reliably elevated in leaky gut, or LPS antibodies. 

Another way is to take an intestinal permeability urine test. You drink a solution containing a pre-measured amount of mannitol and lactulose, two indigestible sugars. Then you collect your urine over the next six hours and measure the amount of excreted mannitol and lactulose to determine how much permeated through your gut.

In more severe cases, your doctor may order a biopsy or endoscopy to measure the permeability of the intestinal lining. 

How to Heal a Leaky Gut

Healing a leaky gut will involve many of the same fundamental practices that you’d use to improve gut health generally.

Eat foods that support the microbiome and avoid foods that disrupt it. Consider adding prebiotics, probiotics, or synbiotics if you aren’t getting plenty through food. Drink bone broth. Eat oysters and red meat for zinc, and supplement if needed.12

Get plenty of sleep and sunshine. Supplement with vitamin D if needed.

Manage stress. 

Quit smoking. 

Limit your use of NSAIDS.

Because your intestinal lining has already sustained damage, and you’re experiencing systemic inflammation as a result, you may need to go a step further. For instance, you might want to do a more stringent elimination diet to identify foods that are particularly problematic for you. And of course, if you are experiencing acute, highly worrisome symptoms like gastric bleeding, see a doctor immediately. 

Last Thing

Interesting, huh? Leaky gut really gets around.

One more point I want to clear up. Leaky gut syndrome is a diagnosis that has been popular in alternative medicine circles for a while, but critics argue that it is too broad and poorly defined. Leaky gut syndrome is not accepted as a diagnosis in mainstream medicine, which has led some folks to dismiss the concept of leaky gut altogether. Don’t be fooled. Leaky gut just refers to higher-than-normal intestinal permeability, which is unquestionably a factor in a plethora of health issues. 

Ok, that’s it for today. Let me know in the comments if you had more questions about leaky gut you’d like me to tackle.

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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