Leaky gut: real phenomenon, misleading term
Leaky gut is one of those phrases that has become widely used, often without much context. It’s mentioned in conversations about digestion, skin issues, fatigue, and even mental health. Some dismiss it entirely, others over-attribute it to everything.
The truth sits somewhere in the middle.
There is a real physiological process behind what people refer to as leaky gut. The more accurate term is increased intestinal permeability. Understanding what that means starts with understanding the gut barrier itself.
What is the gut barrier?
The gut barrier is a highly specialised structure that lines the intestines. Its role is to allow nutrients to pass into the bloodstream while keeping harmful substances out.
This barrier is made up of a single layer of intestinal cells, held together by structures called tight junctions. These act like selective gates, opening and closing in response to signals. Alongside this physical layer, there is also a mucus layer, immune cells, and the gut microbiome, all working together to maintain integrity and protection.
When functioning well, this system is incredibly efficient. It allows the body to absorb what it needs while acting as a barrier against pathogens, toxins, and undigested food particles.
What is increased intestinal permeability?
Increased intestinal permeability occurs when these tight junctions become less selective. Instead of acting as a controlled barrier, they allow substances to pass through more easily than they should. This doesn’t mean the gut is literally “leaking”, but rather that its filtering function is compromised.
Substances that would normally remain within the gut - including bacterial fragments, toxins, and partially digested food components - can cross into the bloodstream. And this is where the immune system becomes involved.
Why does this matter?
The gut is one of the largest immune organs in the body. Around 70% of the immune system is located in or around the GI tract.
When the barrier is compromised, the immune system is exposed to substances it would not normally encounter. This can trigger an immune response, and over time, contribute to low-grade systemic inflammation.
One of the key players in this process is lipopolysaccharide (LPS), a component of the outer membrane of certain bacteria. Under normal conditions, LPS remains within the gut, but when intestinal permeability increases, LPS can enter the bloodstream. Even small amounts can activate the immune system and promote inflammation. This process, sometimes referred to as metabolic endotoxemia, has been linked in research to conditions such as insulin resistance, obesity, and autoimmune conditions.
What causes increased permeability?
Like most things that happen within the body, there isn’t a single driver of increased intestinal permeability - it’s usually the result of multiple factors acting together.
Diet plays a role, particularly patterns that are low in fibre and high in ultra-processed foods. Chronic stress is another key driver, as it directly affects gut function and barrier integrity through the gut-brain axis. Certain medications, including non-steroidal anti-inflammatory drugs (NSAIDs) and repeated courses of antibiotics, can also impact the gut lining.
Infections are another important factor. Gastroenteritis can disrupt the gut barrier, sometimes with longer-term effects on gut function. Dysbiosis, an imbalance in the gut microbiome, can also contribute, particularly when beneficial bacteria that support the gut lining are reduced.
Signs and symptoms
Contrary to popular belief, there isn’t a single symptom that defines increased intestinal permeability, which is part of what makes it difficult to identify.
From a clinical perspective, it’s often seen alongside digestive symptoms such as bloating, abdominal discomfort, changes in bowel habits, and multiple food sensitivities. However, it can also present more systemically - fatigue, brain fog and skin issues are commonly reported.
That said, these symptoms are not specific to permeability alone. They mimic conditions like IBD, IBS, SIBO - which is why clinical context is important.
Why the term “leaky gut” can be misleading
Intestinal permeability is a dynamic process - it can increase and decrease in response to different stimuli, such as stress, intense exercise and certain food proteins. But not every increase is pathological, and not every symptom can be attributed to it.
In clinical practice, considering increased intestinal permeability is important, but only when it’s placed within the right framework. It’s not a diagnosis in itself, and it doesn’t exist in isolation. It’s part of a wider system involving the gut microbiome, the immune system, and overall physiology. The focus should be less on the label and more on what is contributing to those changes. When those factors are addressed, the gut barrier often improves as a result.
Five ways to support a healthy gut barrier
If increased intestinal permeability is influenced by diet, lifestyle, the gut microbiome, and immune function, then supporting the gut barrier requires a multifaceted approach. The good news is that many of the factors known to influence gut barrier integrity are within our control.
Eat a plant-rich, fibre-focused diet
A diverse intake of fruits, vegetables, legumes, whole grains, nuts, and seeds provides fibre and polyphenols, both of which play an important role in maintaining gut barrier function.
Check for key nutrient deficiencies
Several nutrients are involved in maintaining the structure and function of the gut barrier. Deficiencies in vitamin D, vitamin A, and zinc have been associated with impaired barrier integrity and altered immune function. Oily fish, eggs, organ meats, orange-coloured vegetables, legumes, nuts, seeds, and seafood can all help support adequate intake.
Reduce exposure to gut barrier disruptors
Alcohol, smoking, chronic use of certain medications, and diets high in ultra-processed foods have all been associated with impaired gut barrier function. Some food additives, including certain emulsifiers, have also been shown to affect the gut lining and microbiome in experimental studies. While there is no need to obsess over every ingredient, reducing reliance on heavily processed foods is a sensible place to start.
Prioritise stress management
The gut and brain are in constant communication. Chronic stress has been shown to influence gut permeability through the gut-brain axis and may contribute to immune activation and inflammation. Regular exercise, adequate sleep, mindfulness practices, and spending time outdoors can all help regulate the body's stress response.
Support a healthy gut microbiome
A healthy gut barrier depends on a healthy microbiome. Beneficial bacteria help maintain the mucus layer, produce short-chain fatty acids such as butyrate, and support the integrity of the gut lining. Eating a diverse range of plant foods, fibre-rich vegetables, whole grains, legumes, nuts and seeds, is one of the most effective ways to nurture a resilient microbiome. In some cases, fermented foods may also be beneficial, although tolerance varies from person to person.
Product Recommendations
Microbiome Labs MegaMucosa
Invivo Bio.Me Barrier
Thorne GI Relief
Designs for Health GI Revive Powder
All from Healf
Words by Marilia Chamon for The Well Edit.
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