Leaky gut lies behind a host of health problems, here's what it is and how to fix it
If you’ve been dealing with symptoms that don’t seem to connect – digestive issues, skin flares, brain fog, joint pain, hormone issues, exhaustion – and nobody has been able to give you a satisfying explanation, there’s a good chance you’ve started doing your own research. And there’s a good chance that research has led you here.
Leaky gut – or increased intestinal permeability (it’s proper name) – is one of those areas where the science is well ahead of mainstream awareness. Here’s what it actually is, what drives it, and how we approach it.
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Leaky gut: structural integrity
Most people think of gut health in fairly simple terms – digestion, bloating, regularity. But the role your gut plays in your overall health goes much further than that.
A robust, healthy digestive system means being able to:
- Optimally digest and absorb nutrients
- Neutralise and expel toxins
- Reduce inflammation
- Maintain a healthy microbiome
- Maintain structural integrity
Maintaining structural integrity – maintaining a healthy intestinal lining that lets the right things through into the blood stream while keeping undesirable things out – is what we’ll be focusing on in this article.
When this structural integrity is compromised, it’s called ‘increased intestinal permeability’ or, more commonly ‘leaky gut’.
If you’ve heard of leaky gut, or think it may be behind any health challenges you’re experiencing, you may be wondering:
- Exactly what leaky gut is
- How leaky gut happens
- What impact leaky gut has on your health
- And most importantly, what you can do to fix it
By the end of this Coho Health guide to the Functional Medicine approach to leaky gut and intestinal permeability, you’ll have answers to those questions.
What is increased intestinal permeability / leaky gut?
Leaky gut / increased intestinal permeability is where the intestinal barrier that lines the intestinal tract, becomes more permeable – or ‘leaky’ – than it should be.
Specifically, it’s where the tight junctions (that hold the cells of the intestinal lining together) become loose or break completely, and let allergens or pathogens through into the blood stream.
The intestinal barrier is a single layer of cells in the digestive tract that are critical to human health. This barrier has two main regulatory roles:
- It allows for the absorption of nutrients from the food we eat, and prevents against loss of water and electrolytes
- It forms an essential part of our immune system, protecting against the entry of allergens and pathogens (bacteria, fungi, and parasites)
Our gut lining is exposed to everything we swallow, whether that’s food particles, bacteria, pesticides, dust, chemicals, or dirt.
The intestinal barrier must decide what to do with all these things.
Should it allow them to pass through into the blood stream because they are considered beneficial to our health, like nutrients from our food are?
Or should they be kept in the digestive tract to move on through, leaving the body via the bowel as they are considered unhelpful or potentially harmful.
Essentially, the intestinal barrier plays the role of a gatekeeper, and a special protein called Zonulin is what determines how open or closed these gates, known as tight junctions, should be.
This isn’t fringe science – it’s well established in the research:
“The intestinal barrier is essential in human health and forms the interface between the outside and the internal environment of the body ” (1)
When functioning normally, the gut barrier is naturally a little permeable and keeps us healthy by keeping out potentially hazardous materials, while letting nutrients and water in.
But when it starts to become more permeable (or “leaky”) we run into problems.
It might be difficult to imagine, but what is inside our gut isn’t actively inside our body until it passes across this barrier.
When the intestinal barrier malfunctions, and substances that should be eliminated from the body are instead absorbed into the blood steam, inflammation and immune responses are triggered.
The consequences of this can manifest in many different ways and in many different body systems.
A dysfunctional intestinal barrier can, and does, result in increased inflammation.
The inflammatory immune cells in the blood are then carried to other parts of the body.
When this happens, symptoms of a leaky gut can manifest anywhere in the body.
Other barriers also have the potential to be ‘leaky’ – such as the skin barrier, and the blood brain barrier.
Signs and symptoms of leaky gut / increased intestinal permeability
Because the blood carries inflammatory signals to every part of the body, the effects of a leaky gut can show up almost anywhere – which is part of what makes it so easy to miss, and so easy to dismiss.
You might be dealing with digestive symptoms like bloating, reflux, or unpredictable food reactions. Or your symptoms might have nothing obviously digestive about them at all – persistent skin flares, brain fog that makes it hard to think clearly, joint pain that comes and goes, fatigue that sleep doesn’t fix, or mood changes that feel disconnected from what’s actually happening in your life.
For some people it’s one of these things. For many, it’s several – often written off as separate, unrelated problems, when they may all be pointing to the same underlying issue.
Common symptoms include:
Digestion – gas, bloating, reflux, food sensitivities, nutrient deficiencies
Skin – rashes, eczema, acne, rosacea, hives, psoriasis,
Mental – brain fog, headaches, migraines, depression, ADHD
Pain – muscle or joint pain
Energy – fatigue
Allergies – sinusitis, hay fever, frequent infections, sensitivities, histamine intolerance / MCAS
It’s also worth knowing that leaky gut doesn’t always announce itself with obvious symptoms.
For some people, low-grade inflammation is quietly building in the background – contributing to longer term chronic conditions – without any clear warning signs in the present.
If any of this sounds familiar, it’s worth taking seriously.
Conditions associated with leaky gut / increased intestinal permeability
The reach of leaky gut goes further than most people expect. Increased intestinal permeability has been identified as a factor in a wide range of conditions – many of which, on the surface, appear to have nothing to do with the gut:
- IBS
- IBD: Ulcerative colitis & Crohn's disease
- Coeliac disease
- Type 1 and 2 diabetes
- Hashimoto’s thyroiditis
- Rheumatoid arthritis
- Alopecia
- Multiple sclerosis
- Parkinson’s disease
- Polycystic Ovarian Syndrome (PCOS)
- Alcoholic liver disease
- Liver cirrhosis
- Acute pancreatitis
- Chronic heart failure
- Depression (2-5)
- Chronic Fatigue Syndrome / M.E
- Psoriasis
- Acne
- Long COVID
Among many others. If you have a chronic condition that hasn’t responded the way you’d hope to conventional treatment, the gut is often a very good place to start looking.
Common causes of leaky gut / increased intestinal permeability
There are many factors that can interfere with the function of the gastrointestinal system and the intestinal barrier, but common factors include:
Diet
Of all the factors that influence intestinal permeability, diet is often the most significant – and frequently the most actionable. What you eat on a daily basis has a direct impact on the integrity of your gut lining, and in some cases, foods that appear healthy can be part of the problem;
– A pro-inflammatory diet containing high refined carbohydrates, processed oils and sugar has the potential to cause a leaky gut (6)
– Gluten-containing grains (wheat, barley, spelt, rye) can be a trigger for a leaky gut.
Gluten can increase levels of Zonulin, a protein that modulates the intestinal tight junctions.
A high level of Zonulin (a marker we can measure) is more likely to be associated with greater intestinal permeability.
Therefore gluten can be a driver of increased intestinal permeability (7) .
In those with coeliac disease, the potential of developing a leaky gut is greater.
– Dairy can also be a factor in leaky gut.
The protein in milk can damage tight junctions (8) conversely kefir has been shown to be beneficial for a leaky gut (9)
– A diet low in nutrients, lacking in diversity and low in fibre can lead to vitamin deficiencies.
Nutrient deficiencies that may be involved in increasing intestinal permeability include Vitamin A, Vitamin D and Zinc (other nutrients are also important for maintaining a healthy gut barrier). (10 – 12)
– Seemingly healthy foods, such as lentils, beans and chickpeas may also cause a leaky gut in some individuals.
Lectins are proteins found in legumes and grains, and can potentially be a problem for some people, as they can bind to the cells in the intestinal tract and disrupt the barrier.(13)
It is possible to reduce the impact of lectins, by soaking and boiling legumes correctly.
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An unhealthy gastrointestinal system
Sometimes leaky gut isn’t the starting point – it’s the result of an already compromised gut environment. Poor microbiome diversity, existing infections, and conditions like SIBO, IBD, or IBS can all create the conditions in which intestinal permeability develops and worsens.
Infections with candida and Helicobacter Pylori are commonly seen alongside leaky gut – and in clinic, we see this pattern regularly.
Candida and H.pylori both have the potential to pass through the intestinal barrier and increase risk of developing a leaky gut (14,15).
Gastrointestinal infections with gram negative bacteria can also cause a leaky gut, and Lipopolysaccharides (LPS) (bacterial toxins) produced by gram negative bacteria, can translocate through the intestinal barrier and travel to joints.
This is seen in patients with rheumatoid arthritis, or in those with inflammatory skin conditions such as acne or psoriasis, where LPS can drive inflammation and damage.
Mould
Mould exposure is one of the more overlooked drivers of leaky gut – and one that surprises many of our clients when it comes up. Mycotoxins produced by mould can disrupt the gut microbiome, which in turn compromises intestinal permeability (16).
Exposure doesn’t only come from damp buildings or water damaged environments. It can also come through everyday foods – coffee, nuts, and dried fruits in particular – usually as a result of how they’re stored or how long they’ve been stored for. It’s a factor worth considering, especially if other causes have been investigated without clear answers.
Medications
Several commonly prescribed and over-the-counter medications can contribute to leaky gut – particularly when taken regularly or over extended periods. These include steroids, NSAIDs, birth control pills, proton pump inhibitors, and antibiotics.
The NSAID finding is worth highlighting specifically: research suggests that the intestinal barrier can become significantly more permeable within just 24 hours of taking anti-inflammatory medication.
For anyone who relies on NSAIDs regularly – whether for pain, inflammation, or another chronic condition – this is an important consideration, and one where additional gut support can make a real difference.
This isn’t about avoiding necessary medication. It’s about making sure your gut lining is being supported alongside it.
Stress
Stress affects the gut in ways that go deeper than most people realise – and it works in both directions. Both mental and physical stress can increase intestinal permeability.
Physical stressors include:
- Inflammation
- Obesity
- Blood sugar dysregulation
- Sleep
- Over exercising – see below
One of the more significant mechanisms is the effect of chronic stress on digestive capacity.
When the body is under sustained stress, production of digestive enzymes and hydrochloric acid drops. This means food isn’t being broken down properly – which in turn drives food sensitivities, dysbiosis, and increased intestinal permeability.
In other words, stress doesn’t just affect how you feel. It directly affects how well your gut functions.
Managing stress isn’t a lifestyle nicety – for many of our clients, it’s a clinical priority.
Intense exercise
Regular exercise supports gut health – but there’s an important distinction between regular movement and strenuous, high intensity training. For those who exercise at a high level, whether that’s endurance sports, intense gym training, or physically demanding work, the gut can come under significant stress.
Strenuous exercise has been shown to increase intestinal permeability – and for some people, it’s a factor that’s never been considered as part of the picture. If you train hard and also experience gut symptoms, low energy, or frequent illness, it’s worth factoring your exercise load into the conversation.
Sleep
Sleep is one of the most underestimated factors in gut health. Poor or disrupted sleep has been linked to leaky gut through two key mechanisms – dysbiosis (an imbalance in the gut microbiome) and increased levels of lipopolysaccharides (LPS), bacterial toxins that can drive systemic inflammation when they cross the gut barrier (18).
What makes this particularly relevant is how common sleep disruption is – and how rarely it gets factored into gut health investigations.
If you’re dealing with persistent gut symptoms alongside poor sleep, the two could be connected.
Addressing sleep isn’t separate from healing your gut – for many people, it’s part of the same process.
The conventional medicine approach to leaky gut / increased intestinal permeability
Well, there isn’t a conventional medicine approach to leaky gut / increased intestinal permeability.
Unfortunately, there is no perfect test to diagnose a leaky gut, and it cannot physically be seen in endoscopies or colonoscopies.
Generally speaking, within conventional medicine, increased intestinal permeability is not recognised as a physiological state that can contribute to chronic symptoms or chronic health problems, or is not recognised as a physiological state at all.
In fact, the reason we’re frequently referring to this physiological state as ‘increased intestinal permeability’ as well as ‘leaky gut’, is that ‘increased intestinal permeability’ is the proper medical term for leaky gut.
If you do speak to a medical professional, and start talking about your leaky gut, we wouldn’t want you to receive an (at best) polite look of ‘here we go again’.
And, let’s be honest, a ‘leaky gut’ doesn’t sound very scientific.
However, regardless of what we call it, increased intestinal permeability is a ‘thing’, has been scientifically researched, and is extremely well documented in the literature.
Below are the some of the testing options we currently use in a Functional Medicine approach to leaky gut.
Testing options to identify leaky gut / increased intestinal permeability
A comprehensive stool test can specifically test for the Zonulin (the gate keeper) and if Zonulin is high, this can be indicative of a leaky gut.
This test also assesses for gastrointestinal infections and dysbiosis factors that can contribute to a leaky gut.
The below test result is from a comprehensive stool test, and shows high levels of Zonulin:
A Lactose Mannitol Home Test is the gold standard among some conventional medical practitioners.
This test involves drinking a sugar solution of lactose and mannitol (sugars of different molecular weights) and then a urine sample is collected a few hours later.
Levels of the different sugars in the urine are measured and this helps to identify the degree of intestinal permeability. (19)
Mannitol serves as a marker of trans-cellular uptake and lactulose (which should only be very slightly absorbed), serves as a marker for mucosal integrity.
A high lactulose to mannitol ratio indicates increased intestinal permeability.
The Functional Medicine approach to leaky gut / increased intestinal permeability
Leaky gut can be healed – but the approach needs to be systematic.
Throwing supplements at the problem without understanding what’s driving it is one of the most common reasons people go around in circles for years.
The functional medicine 5R framework is a step by step strategy designed to address the root causes of poor gut health methodically.
It’s adapted for each individual based on their symptoms, health history, and test results.
The ‘5 R’ Approach
Remove
The first step is identifying and removing whatever may be disrupting gut function – and that goes broader than simply what’s damaging the gut lining.
Triggers can include factors that disrupt the microbiome, dysregulate the immune system, impair metabolic health, or drive inflammation more broadly.
This might be specific foods that are driving sensitivity reactions, environmental factors such as mould exposure, or infections such as Helicobacter Pylori, candida, a bacterial overgrowth or pathogenic parasitic infection.
For many people, this stage alone brings noticeable relief – because the thing that’s been perpetuating the problem is finally being addressed directly.
But it’s also the stage that requires the most careful investigation, because removing the wrong things – or missing the real triggers entirely – means the subsequent steps are building on an unstable foundation.
Replace
In this stage, we focus on restoring what the digestive system needs to function properly.
This could mean supporting hydrochloric acid levels, pancreatic enzymes, or bile acids – the foundations of good digestion that chronic stress, poor diet, and certain medications can deplete over time.
Increased food reactions are frequently a sign that protein digestion in particular needs support.
Reinoculate
This step is about rebuilding a healthy, diverse microbiome. But it’s rarely as simple as taking an off-the-shelf probiotic and hoping for the best – and in clinic, we see this regularly.
Not all probiotics are well tolerated by everyone, and the wrong strain at the wrong dose can sometimes make symptoms worse before they get better.
The approach we take is considerably more considered. Where we have stool test results, we can see exactly which groups of bacteria, species, or specific strains need support – and tailor the reinoculation accordingly.
Someone with methane-dominant dysbiosis needs a very different approach to someone with low beneficial bacteria diversity or a fungal overgrowth. Dose, timing, and the form of probiotic – whether that’s live bacteria or soil-based organisms, which are often better tolerated by those with sensitivities – all form part of that decision.
Prebiotic fibres and resistant starches are also introduced carefully and at the right stage – because feeding bacteria before the environment is ready can fuel the wrong ones.
This is one of the areas where working with a practitioner who can interpret your test results makes the most significant difference to outcomes.
Repair
This is arguably the most important stage of the entire process = and for many people, it’s the point where things finally start to shift in a meaningful way.
It’s not uncommon for clients to move through the remove and replace stages without feeling dramatically different. That’s not a sign that the earlier steps haven’t worked – they’re laying essential groundwork.
But it’s often during the repair stage that the cumulative effect becomes noticeable.
Inflammation begins to settle. The immune system starts to rebalance. Energy improves. Foods that previously triggered reactions become tolerable again. That broader sense of things feeling calmer in the body – less reactive, less unpredictable – is something we hear consistently from clients at this stage.
The repair stage works by directly supporting the integrity of the gut lining itself through targeted nutrients.
These include vitamin A, vitamin D, zinc, L-glutamine, collagen, and colostrum – each playing a specific role in restoring the intestinal barrier.
Foods like bone broth and fish stock provide natural sources of collagen and glutamine and can be a valuable part of this stage alongside supplemental support.
How long repair takes varies from person to person – it depends on how long the gut lining has been compromised, what the underlying drivers were, and how well the earlier stages have been implemented.
But for most people, this is the stage where the investment in the process starts to feel worth it.
Rebalance
This final step is the one most often underestimated – and the one most responsible for whether results last.
Rebalance is about the lifestyle foundations that keep the gut healthy long term: managing the gut-brain axis, maintaining microbiome diversity, reducing reliance on medications where possible, spending time in nature, and building sustainable stress reduction into daily life.
Without this step, it’s easy to make progress and then slowly slide back. With it, the improvements tend to stick.
Foods that can support the repair of a leaky gut
Food plays a foundational role in the repair of a leaky gut:
– Glutamine and collagen are both important, and are found in bone broths and fish stocks
– Omega 3 fatty acids like those found in oily fish, algae, seaweeds, flaxseeds and walnuts are also important
– Vitamin D, which is predominately obtained from sunlight exposure, but a small amount in mushrooms and eggs
– Vitamin A is found in organ meats, and red and yellow coloured vegetables
– Quercetin, found in apples, onion and garlic.
– Zinc found in pumpkin seeds and shellfish like oysters
When diet alone isn’t able to meet your nutritional requirements, then high quality nutritional supplements can be helpful.
Other supplemental support, such as colostrum, immunoglobulins and butyrate also support the gut lining and the microbiome.
How long does it take to heal a leaky gut?
The length of time required to repair a leaky gut can depend on the underlying conditions and potentially, on how long the intestinal barrier has been dysfunctional for.
It could, for example, take anywhere between 4 weeks to 6 months (in more complex cases).
For most people, we’d say around 2-3 months.
Can fixing your intestinal permeability arrest progression of autoimmune disease?
The short answer is: yes – and for anyone living with an autoimmune condition, that’s worth sitting with for a moment.
We know that increased intestinal permeability is found consistently in people with autoimmune disease. The precise nature of that relationship is still being explored – whether leaky gut triggers autoimmunity, whether autoimmunity drives leaky gut or whether the two reinforce each other in both directions.
But what the research makes increasingly clear is that addressing intestinal permeability is a meaningful and often underutilised part of managing autoimmune conditions.
Here’s why. When the gut barrier is compromised, it isn’t only harmful pathogens that cross into the bloodstream. Even commensal bacteria – the so called ‘good’ bacteria that are supposed to remain inside the gut – can escape the intestinal lumen and trigger an immune response.
The resulting inflammation doesn’t stay localised. It travels. And when the immune system is repeatedly exposed to these triggers, the dysregulation that follows can manifest as, or accelerate, autoimmune disease (20).
Leaky gut, in this context, acts as a gateway – not just to digestive symptoms, but to a pattern of systemic inflammation that the immune system struggles to resolve on its own.
The body has a remarkable capacity to recover when the right conditions are created. For many people with autoimmune conditions, investigating and addressing intestinal permeability is one of the most important steps they haven’t yet taken – and one that conventional investigation rarely reaches.
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The wrap...
If you’ve read this far, there’s a good chance leaky gut isn’t just an abstract concept for you – it’s something you suspect may be relevant to your own health.
And if you’ve been dealing with symptoms across multiple body systems, perhaps for years, without ever having your gut function properly investigated, that suspicion is worth taking seriously.
The good news is that increased intestinal permeability is not a life sentence. With the right investigation, a clear picture of what’s driving it, and a systematic approach to addressing those drivers in the right order, the gut lining can heal – and the broader effects of that healing, on immunity, inflammation, energy, skin, and mood, can be profound.
If you’ve already tried a lot of things without lasting results, that’s not a reflection of you. It’s a reflection of whether the underlying causes have ever been properly investigated. That’s exactly where we start.
If you think the Coho functional medicine approach to leaky gut can help you, you can book a free 15 minute discovery call with us here.
We work with clients in the UK and with people around the world through our virtual clinic – so wherever you are, we can help.
To your optimised, healthy future,
Lulu & the Coho Health team
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