Leaky gut is a condition in which bacteria and toxins “leak” through the intestinal wall. Though many medical professionals do not recognize it, scientific evidence suggests it is related to many health issues.

A phenomenon called “leaky gut” has recently gained quite a bit of attention, particularly among natural health enthusiasts. It is also known as increased intestinal permeability.

This article takes a critical look at the evidence on leaky gut syndrome.

What Is Leaky Gut?

The human digestive tract is where food is broken down and nutrients are absorbed.

The digestive system also plays an important role in protecting your body from harmful substances. The walls of the intestines act as barriers, controlling what enters the bloodstream to be transported to your organs.

Small gaps in the intestinal wall called tight junctions allow water and nutrients to pass through, while blocking the passage of harmful substances. Intestinal permeability refers to how easily substances pass through the intestinal wall.

When the tight junctions of intestinal walls become loose, the gut becomes more permeable, which may allow bacteria and toxins to pass from the gut into the bloodstream. This phenomenon is commonly referred to as “leaky gut.”

When the gut is “leaky” and bacteria and toxins enter the bloodstream, it can cause widespread inflammation and possibly trigger a reaction from the immune system.

Supposed symptoms of leaky gut syndrome include bloating, food sensitivities, fatigue, digestive issues and skin problems (1).

However, leaky gut is not a recognized medical diagnosis. In fact, some medical professionals deny that it even exists.

Proponents claim that it’s the underlying cause of all sorts of conditions, including chronic fatigue syndrome, migraines, multiple sclerosis, fibromyalgia, food sensitivities, thyroid abnormalities, mood swings, skin conditions and autism.

The problem is that very few scientific studies mention leaky gut syndrome.

Nevertheless, medical professionals do agree that increased intestinal permeability, or intestinal hyperpermeability, exists in certain chronic diseases (1, 2).

Leaky gut, or intestinal hyperpermeability, is a phenomenon that occurs when the tight junctions of the intestinal wall become loose, allowing harmful substances to enter the bloodstream.

What Causes Leaky Gut?

Leaky gut syndrome remains a bit of a medical mystery, and medical professionals are still trying to determine exactly what causes it.

A protein called zonulin is the only known regulator of intestinal permeability (3, 4).

When it’s activated in genetically susceptible people, it can lead to leaky gut. Two factors that trigger the release of zonulin are bacteria in the intestines and gluten, which is a protein found in wheat and other grains (3, 4, 5).

However, some studies have shown that gluten only increases intestinal permeability in people with conditions like celiac disease or irritable bowel syndrome (6, 7).

There are likely multiple contributing factors to leaky gut syndrome.

Below are a few factors that are believed to play a role:

• Excessive sugar intake: An unhealthy diet high in sugar, particularly fructose, harms the barrier function of the intestinal wall (8, 9).
• Non-steroidal anti-inflammatory drugs (NSAIDs): The long-term use of NSAIDs like ibuprofen can increase intestinal permeability and contribute to leaky gut (10, 11, 12).
• Excessive alcohol intake: Excessive alcohol intake may increase intestinal permeability (10, 13).
• Nutrient deficiencies: Deficiencies in vitamin A, vitamin D and zinc have each been implicated in increased intestinal permeability (8, 14, 15).
• Inflammation: Chronic inflammation throughout the body can contribute to leaky gut syndrome (16).
• Stress: Chronic stress is a contributing factor to multiple gastrointestinal disorders, including leaky gut (17).
• Poor gut health: There are millions of bacteria in the gut, some beneficial and some harmful. When the balance between the two is disrupted, it can affect the barrier function of the intestinal wall (1, 8).
• Yeast overgrowth: Yeast is naturally present in the gut, but an overgrowth of yeast may contribute to leaky gut (18).

Medical professionals are still trying to determine what causes leaky gut syndrome. An unhealthy diet, long-term NSAID use, stress and chronic inflammation are some factors that are believed to contribute to it.

Diseases Associated With Leaky Gut

The claim that leaky gut is the root of modern health problems has yet to be proven by science. However, many studies have connected increased intestinal permeability with multiple chronic diseases (3).

Celiac Disease

Celiac disease is an autoimmune disease characterized by a severe sensitivity to gluten.

Several studies have found that intestinal permeability is higher in patients with celiac disease (1, 6, 7).

In fact, one study found that ingesting gluten significantly increases intestinal permeability in celiac patients immediately after consumption (6).

Diabetes

There is some evidence that increased intestinal permeability plays a role in the development of type 1 diabetes (1).

Type 1 diabetes is caused by an autoimmune destruction of insulin-producing beta cells in the pancreas (19).

It has been suggested that the immune reaction responsible for beta cell destruction may be triggered by foreign substances “leaking” through the gut (20, 21).

One study found that 42% of individuals with type 1 diabetes had significantly elevated zonulin levels. Zonulin is a known moderator of intestinal permeability (22).

In an animal study, rats that developed diabetes were found to have abnormal intestinal permeability prior to developing diabetes (23).

Crohn’s Disease

Increased intestinal permeability plays a significant role in Crohn’s disease. Crohn’s is a chronic digestive disorder characterized by persistent inflammation of the intestinal tract (1, 24, 25).

Several studies have observed an increase in intestinal permeability in patients with Crohn’s disease (26, 27.)

A few studies also found increased intestinal permeability in relatives of Crohn’s patients, who are at an increased risk of developing the disease (26, 28).

This suggests that increased permeability may be connected to the genetic component of Crohn’s disease.

Irritable Bowel Syndrome

Studies have found that people with irritable bowel syndrome (IBS) are likely to have increased intestinal permeability (29, 30).

IBS is a digestive disorder characterized by both diarrhea and constipation. One study found that increased intestinal permeability is particularly prevalent in those with diarrhea-predominant IBS (31).

Food Allergies

A few studies have shown that individuals with food allergies often have impaired intestinal barrier function (32, 33).

A leaky gut may allow food proteins to cross the intestinal barrier, stimulating an immune response. An immune response to a food protein, which is known as an antigen, is the definition of a food allergy (10).

Multiple studies have demonstrated that increased intestinal permeability is indeed present in people with certain chronic diseases.

Is Leaky Gut a Cause or Symptom of Disease?

Proponents of leaky gut syndrome claim it’s the underlying cause of most modern health problems.

Indeed, plenty of studies have shown that increased intestinal permeability is present in several chronic diseases, specifically autoimmune disorders.

However, it is difficult to prove that leaky gut is the cause of disease.

Skeptics argue that increased intestinal permeability is a symptom of chronic disease, rather than an underlying cause (34).

Interestingly, animal studies on celiac disease, type 1 diabetes and IBS have identified increased intestinal permeability prior to the onset of disease (23, 34, 35).

This evidence supports the theory that leaky gut is involved in the development of disease.

On the other hand, a study found that intestinal permeability in people with celiac disease returned to normal in 87% of people who followed a gluten-free diet for over a year. A gluten-free diet is the standard treatment for celiac disease (36).

This suggests that the abnormal intestinal permeability may be a response to gluten ingestion, rather than the cause of celiac disease.

Overall, there is not yet sufficient evidence to prove that leaky gut is the underlying cause of chronic diseases.

Studies have consistently shown that increased intestinal permeability is present in several chronic conditions. However, there is no conclusive evidence that leaky gut is the underlying cause of them.

Some Claims About Leaky Gut Syndrome Are Not Backed by Science

There is enough evidence to demonstrate that leaky gut syndrome does exist. However, some of the claims being made are not backed by science.

Proponents of leaky gut have claimed that it’s connected to a wide variety of ailments, including autism, anxiety, depression, eczema and cancer. Most of these claims have yet to be proven by scientific studies.

A few studies have found that a proportion of autistic children have increased intestinal permeability, but other studies have found that intestinal permeability was normal (37, 38, 39).

Currently, there are no studies that show leaky gut presence prior to the onset of autism, which means there is no evidence that it is a causative factor.

There is some evidence that bacteria crossing the intestinal wall may play a role in anxiety and depression, but more research is needed to prove this possible connection (40, 41, 42).

The results of studies on eczema and intestinal permeability have been inconsistent, and there is currently no scientific basis for the claim that leaky gut leads to cancer (43, 44, 45).

Furthermore, some of the proposed treatments for leaky gut syndrome have weak scientific support.

Many supplements and remedies being sold by websites have not yet been proven to be effective (34).

There is sufficient evidence to demonstrate that leaky gut syndrome exists. However, science has not yet proven that conditions like autism or cancer are related to leaky gut syndrome.

How to Improve Your Gut Health

Leaky gut syndrome is not an official medical diagnosis and there is not yet a recommended course of treatment.

Nevertheless, there are steps you can take to improve your gut health. One of the keys to a healthier gut is increasing the number of beneficial bacteria in it.

Here are a few strategies to support a healthy gut:

• Limit your refined carb intake: Harmful bacteria thrive on sugar, and excessive sugar intake can harm gut barrier function (8, 9, 46).
• Take a probiotic supplement: Probiotics are beneficial bacteria that can improve your gut health. Probiotic supplements have been shown to be beneficial for gastrointestinal diseases (47, 48, 49, 50, 51).
• Eat fermented foods: Fermented foods, such as plain yogurt, kimchi, sauerkraut, kefir and kombucha, contain probiotics that can improve gut health (49, 52, 53).
• Eat plenty of high-fiber foods: Soluble fiber, which is found in fruits, vegetables and legumes, feed the beneficial bacteria in your gut (8, 54, 55).
• Limit the use of NSAIDs: The long-term use of NSAIDs like ibuprofen contributes to leaky gut syndrome (10, 11, 12).

Increasing the friendly bacteria in your gut can improve your gut health and help prevent leaky gut syndrome.

The Bottom Line

Leaky gut, or increased intestinal permeability, is a condition in which bacteria and toxins are able to pass through the intestinal wall into the bloodstream.

Some medical professionals deny that leaky gut exists, but there is quite a bit of evidence to confirm that increased intestinal permeability is real.

For example, leaky gut syndrome is present in several autoimmune disorders.

However, there is not enough evidence to conclude that leaky gut syndrome is the underlying cause of these diseases.

To decrease your risk of leaky gut syndrome, focus on improving your gut health by eating a healthy diet and limiting your use of NSAIDs.