Blog Post

Leaky Gut: A Dietitian’s Review Of The Research

Leaky gut

Leaky gut is a hot topic of debate in the medical field. Some medical professionals don’t believe it to be a real condition, whilst others associate it with a range of symptoms and disease states. 

Research on leaky gut otherwise known as increased intestinal permeability seems to be a bit of a hot mess. Hence why it is not a widely accepted condition but also why it can’t be completely refuted. 

Proponents of leaky gut syndrome have linked the condition with a variety of other medical conditions and diseases. Saying that leaky gut is the underlying cause of chronic fatigue syndrome, food sensitivities, fibromyalgia, autism, and skin conditions amongst other things. 

Typically, the professionals diagnosing and treating leaky gut come from the natural health space such as naturopaths and homeopaths. 

On the other hand, traditional medicine is not so clear on whether “leaky gut” or intestinal permeability has any clinical relevance and does not recognize or attempt to treat this condition. 

This may be because intestinal permeability isn’t touted as the root cause of particular health problems in research. But simply one of the internal mechanisms between certain factors and their role in disease and other conditions. 

As it stands we know that:

  • Intestinal hyperpermeability is a real physiological phenomenon that does occur
  • The permeability of the intestine can be increased and decreased based on a variety of dietary and lifestyle factors, medications, disease states and nutrient availability 

What we don’t know:

  • Whether a ‘leaky gut’ is the cause or a contributor to certain disease states 
  • If reducing intestinal permeability in those with ‘leaky gut’ has any clinic outcomes on disease states or symptoms of certain conditions 

What is Leaky Gut?

The digestive tract is where food is broken down and nutrients are absorbed into the body’s circulatory system.

The human digestive system tightly regulates what passes through into the blood and what continues through the digestive tract to be eventually disposed of as waste.

Small gaps in the intestinal walls, called tight junctions, allow water and nutrients to pass through but typically stop larger particles such as bacteria and toxins from passing. 

However, when intestinal hyperpermeability is present and the tight junctions are not as tightly regulated as they should be, these larger particles are able to pass through the intestinal wall and into the bloodstream. 

The leaky gut theory proposes that a more permeable bowel lining can lead to many issues with digestion, immunity, and disease states due to the translocation of pathogens and endotoxins from the digestive tract. 

how does leaky gut work?

Whilst intestinal hyperpermeability is a real phenomenon verified in research, it is the link to other conditions that is questionable and still under investigation. 

One of the main reasons that the traditional medical establishment doesn’t recognize leaky gut as a real condition is due to the bold claims made by some alternative medicine practitioners. 

One podcast from Dr. Josh Axe, a Naturopath, was titled, “Leaky gut syndrome is the root cause of all disease”. And that accurately summarizes how a good portion of natural health practitioners see leaky gut. 

Despite the fact that the evidence is incredibly mixed and there is still a lot we don’t know about the condition.  

Many naturopaths will also sell their patients a number of supplements in order to cure leaky gut, again, even though research for this is still very much in the early stages.

How Do You Test For Leaky Gut?

The most used test for leaky gut or intestinal permeability research is the lactulose-mannitol challenge. 

In this test, the patient takes a solution of mannitol and lactulose, and a urine sample is collected six hours later. An elevated ratio of lactulose and mannitol in the urine, above what is expected, indicates intestinal hyperpermeability.

Lactulose-mannitol-tests-leaky-gut

However, it is important to note that interpretive problems can occur in this type of testing. So although it is predominantly used in a research setting, the availability of at-home testing kits is questionable. 

Results can be affected by hydration status and the size of the person the sample was from. There have even been cited differences in average results depending on geographical location. 

The Chicken or The Egg Scenario of Leaky Gut 

We do know that certain disease states and stressors on the body are linked to increased intestinal permeability.

However, the increased intestinal permeability may be a symptom of these conditions rather than the cause or a contributing factor.  

For example, several studies have found that people with coeliac disease have increased intestinal permeability. But what is to say that the “leaky gut” is not just a by-product of coeliac disease. 

It is also plausible that some conditions increase intestinal permeability whilst for others it is a contributing factor to disease progression. 

In most cases, leaky gut can not be said to have a cause and effect relationship with certain diseases and medical conditions. Mostly, we just know that there is some correlation. That correlation may be cause and effect in one direction or the other or it may even be bidirectional.

Gut Health & Leaky Gut

It has been proposed that poor gut health can increase intestinal permeability. In fact, a leaky gut may be one of the links between the gut microbiome and disease. 

The gut microbiome is a complex ecosystem of bacteria within our digestive tract. Relatively new research has shown that the gut microbiome plays a huge role in many facets of health even outside of the gut.

Whilst evidence is still evolving in this space, we do know that many dietary and lifestyle factors can reduce the health of the gut microbiome. 

This is also known as gut dysbiosis which refers more specifically to an overgrowth of bad bacteria in the gut and/or a reduction in good bacteria.

The gut microbiome regulates host metabolism, immunity, and intestinal barrier function. 

In the case of dysbiosis where there is an increase in the number of harmful bacteria in the gut, releasing enterotoxins, tight junction protein expression can be affected leading to increased permeability of the intestinal wall.

Increased gut permeability may explain the link between gut dysbiosis (overgrowth of bad bacteria) and effects on systems outside of the gastrointestinal system such as mental health and chronic disease.

Leaky Gut & Disease – The Potential Link

The link between increased intestinal permeability and disease likely has something to do with the translocation of whole bacteria and bacterial products such as metabolites from the gut and into the circulatory system.

Basically meaning that these things that would usually stay within the gastrointestinal tract are making it into the body’s circulatory system and then into distant tissues because the intestinal wall has become more permeable.

This may be contributing to remote organ injury and inflammation. 

It is a very interesting concept because for many diseases such as heart disease, we don’t typically think about treating the gut.

But if this theory is correct and changes in the gut are predisposing people to a myriad of chronic diseases, potentially we should be paying far more attention to overall gut health. 

Factors That Reduce Gut Health & Increase Intestinal Permeability

Diet

High-calorie, high-fat, and low fiber diets remain one of the major contributors to gut microbiome dysbiosis and damage intestinal tissues creating a “leaky gut”.

From a dietary perspective, it is likely a good idea to focus on all of the strategies we have currently to nurture our gut microbiome.

That could include a diet rich in fiber, prebiotic-rich foods, and a wide variety of plant-based foods. 

Alcohol

Chronic alcohol consumption may increase gut permeability to endotoxins. This may initiate injury to the liver and other organs since the endotoxins would be in the circulatory system. 

Therefore, increased intestinal permeability may be a contributor to alcohol-related conditions such as liver cirrhosis.

One study demonstrated that increased intestinal permeability occurred in a subgroup of alcohol-dependent subjects who also had an altered gut microbiota profile or dysbiosis (overgrowth of bad bacteria in the gut).  

Stress

Gut brain axis

Interestingly in the same study, higher intestinal permeability was also associated with higher stress, depression, and anxiety scores.

Stress can negatively impact the intestinal barrier and has been associated with an increase in gut permeability.  Indeed, the effects of stress on intestinal permeability are complex and likely involve both the gut and the brain.

There is a bidirectional link between the gut and the brain which is commonly referred to as the gut-brain axis.

If you have ever had butterflies in your stomach or the sensation of a ‘gut feeling’, those are great examples of how the gut and the brain are intimately connected. 

Your gut contains 500 million neurons, which are connected to your brain through nerves. The vagus nerve is the largest nerve that connects your brain and your gut and signals travel in both directions through this particular nerve. 

It has been suggested that strong emotions such as stress, anxiety, and depression might affect microbiota composition and reduce the function of the intestinal wall as a barrier.

Increased intestinal permeability may allow toxins and pathogens to pass through the blood-brain barrier and further contribute to neurological and psychological conditions. 

Therefore, we have this physiological mechanism that loops around. Poor mental health and stress can lead to reductions in gut health and reductions in gut health and increased intestinal permeability may be further contributing to those psychological conditions and mental states. 

Obesity 

Obesity has also been associated with increased gut permeability

Whilst this hasn’t been confirmed in human studies, animal models have shown that there is similar communication between the gut and adipose (fat) tissue such as that seen with the gut-brain axis. 

When obesity is present, changes in the microbiome are responsible for the development of low-grade inflammation that impairs the function of the intestinal barrier. Once again this leads to toxins passing through the gut barrier and into the circulatory system. 

It has been suggested that this may somewhat explain the link between obesity and metabolic syndrome and insulin resistance. 

Moreover, research shows that weight loss brings gut permeability back to the normal range.

Other Factors

In addition to all of the factors above, other lifestyle and environmental factors may lead to gut dysbiosis, increase intestinal permeability, and potentially increase susceptibility to a range of conditions. 

These other factors include a lack of or poor sleep, antibiotic and anti-inflammatory usage, sedentary lifestyles, chronic environmental noise (including traffic, media, and household appliances) and even being subjected to the heat or cold for extended periods of time. 

We also know that increased permeability can be the result of major burns or injury, chemotherapy, radiotherapy of the abdomen, gut infections, and can even occur during endurance exercise.

However, it is still not clear what relevance this all has to health. Under certain conditions, intestinal permeability may leave us more susceptible to certain health conditions or symptoms, but it is more likely that is a culmination of risk factors that determines a particular outcome.

That is why we should be wary of practitioners who are diagnosing and treating leaky gut as a root cause of a disease or condition. 

It is also important to note that much of this research is still in its infancy and based on animal models. 

Animal research models translation to humans

Medical Conditions Associated With Leaky Gut 

There is not a lot of merit in summarising the evidence for each and every disease or medical condition that has been linked to ‘leaky gut’ or increased intestinal permeability. 

As previously stated, we are in a bit of a chicken or the egg scenario. Even if ‘leaky gut’ is present alongside a medical condition, we can’t be sure that correlation equals causation. 

At the end of the day, we believe intestinal permeability is linked with many conditions such as: 

  • Inflammatory bowel disease 
  • Coeliac disease
  • IBS
  • Type 1 diabetes
  • HIV/AIDS
  • Cystic fibrosis
  • Heart disease
  • Non-alcoholic liver disease
  • Rhemotoid arthitis 
  • Multiple sclerosis
  • Asthma
  • Food intolerances and allergies 

But the clinical relevance is mostly unknown. It is likely that intestinal permeability plays a very complex role within very complicated physiological mechanisms that we are just scratching the surface of.

Leaky Gut, Zonulins & Gluten

Something that is discussed a lot within the leaky gut conversation, is the potential negative effect of consuming gluten.

Gluten is a protein that is found in wheat-based products such as bread.

Gluten can activate zonulin activity in some people, which leads to increased intestinal permeability. Zonulins are also a protein. They are found in the body and they regulate the tight junctions in the small intestine.

Some research has shown that gluten consumption affects zonulin activity and subsequently results in increased intestinal permeability or ‘leaky gut’.

The catch is that this only occurs in those with gluten-specific medical conditions. Namely, coeliac disease.

It may also occur in non-coeliac gluten sensitivity. However, gluten consumption does not cause ‘leaky gut’ in people who do not have an existing intolerance or allergy to gluten protein.

Cures For Leaky Gut 

Supplements and ‘cures’ for leaky gut are where the water starts to get muddy from an ethical perspective. 

As a dietitian, we aim to be as evidence-based as possible. Meaning that we need scientific and sound evidence to inform our practice. 

Currently, we don’t even know the effects of ‘leaky gut’ or whether addressing leaky gut has any actual outcomes in relation to disease risk, disease progression, or symptoms of certain conditions. 

However, research has been done looking into potential ways we can restore intestinal permeability to ‘normal’ levels when increased permeability is present. 

Studies in non-human models suggest that certain nutrients such as vitamin D, polyphenols, and zinc may restore gut barrier function. These do actually make sense as all three have already been linked to gut health in general. 

For example, vitamin D deficiency may exacerbate IBS symptoms, a diet rich in polyphenols helps to regulate the gut microbiome and zinc is critical for the health of the intestinal mucosa. 

Surprising effects have also been reported for specific amino acids such as glutamine and tryptophan.

Glutamine specifically is essential for regulating the tight junction proteins between cells in the gut lining. 

So when glutamine levels are low or are being glutamine is being used extensively but the body such as in burns victims, increased intestinal permeability is often present. 

In these cases, glutamine supplementation may be useful but more research is required in this space.

If you want to read more about glutamine supplementation and gut health, check out our deep dive here. 

Conclusion & A Key Take-Away

There is absolutely a complicated relationship between the gut microbiome, intestinal permeability, diet, lifestyle, and disease.

How all the pieces of this puzzle fit together is still very much under investigation and the research is only hitting the top of the iceberg currently. 

Nonetheless, if ‘leaky gut’ does concern you it is probably beneficial to:

  1. Have a diet rich in fibre, based on a variety of plant foods
  2. Avoid excessive calorie and fat consumption 
  3. Avoid excessive alcohol consumption
  4. Lead an active lifestyle 
  5. Aim to be a healthy weight 
  6. Avoid the long term use of antibiotics and anti-inflammatory medications 
  7. Avoid vitamin D and zinc deficiency 
  8. Have enough good quality sleep 
  9. Live in an area without chronic noise pollution 
  10. Reduce stress levels and take care of your mental health 

All of these points are things we already know would be good for us. So knowing that ‘leaky gut’ may be a part of the big picture of health, doesn’t really change how we actually manage our risk of disease. Not yet anyway. 

By Leah Higl

Leah is an accredited practising dietitian from Brisbane. She also competes as an under 75kg powerlifter with Valhalla Strength Brisbane. As both an athlete and dietitian, she spends much of her time developing her knowledge and skills around sports nutrition, specifically for strength-based sports. Although, she works with a range of athletes from triathletes to combat sports and powerlifting. Leah also follows a plant-based diet and her greatest passion is fuelling vegan/vegetarian athletes and proving that plant-based athletes can be just as competitive as their non-vegan counterparts.​