Leaky gut: symptoms, causes and how your microbiota can help

Bloating, gas, fatigue, headaches, irritated skin, and reactions to foods you used to tolerate well. Apparently disconnected symptoms that conventional tests can't explain. If these sound familiar, your intestinal barrier may not be doing its job properly.

Leaky gut — or increased intestinal permeability — is a phenomenon increasingly documented in scientific literature and increasingly overlooked in medical consultations. It's not a disease in itself, but the result of an imbalance in gut microbiota with consequences throughout the body.

What is leaky gut?

The intestine is lined by a layer of epithelial cells joined together by structures called "tight junctions." These junctions act as a selective barrier: they allow the nutrients the body needs to pass through while blocking bacteria, toxins, and undigested particles.

When this barrier deteriorates — due to dysbiosis, chronic stress, poor diet, or prolonged antibiotic use — the tight junctions loosen. The gut becomes "leaky": it allows substances that shouldn't enter the bloodstream to pass through, including bacterial fragments, partially digested proteins, and toxins.

This triggers an immune and inflammatory response that can manifest in very varied symptoms that are difficult to attribute to the gut.

Leaky gut symptoms

Leaky gut has no single defining symptom — and that's what makes it especially difficult to detect. The most common are:

Digestive symptoms:

• Persistent abdominal bloating
• Frequent and uncomfortable gas
• Alternating diarrhea or constipation
• Slow and heavy digestion
• Intolerance to foods previously tolerated

Systemic symptoms (outside the gut):

• Chronic fatigue and brain fog
• Frequent headaches
• Skin problems (eczema, psoriasis, acne)
• Joint pain without apparent cause
• New food allergies or sensitivities
• Mood changes, anxiety, or mild depression
• Frequent infections (weakened immune system)

The dispersion of these symptoms is what causes so many people to spend years without a clear diagnosis.

Main causes of leaky gut

Leaky gut doesn't appear overnight. It's the result of accumulated factors that erode the intestinal barrier:

1. Gut dysbiosis

Microbiota imbalance is the most frequent and most overlooked cause. When beneficial bacteria decrease and pathogenic ones proliferate, the mucus layer protecting the intestinal epithelium thins, tight junctions degrade, and permeability increases. Dysbiosis and leaky gut feed each other: one worsens the other.

2. Ultra-processed food

Refined sugar, industrial emulsifiers (like polysorbate 80 or carboxymethylcellulose), preservatives, and artificial sweeteners directly damage tight junctions and alter microbiota composition. A low-fiber diet deprives beneficial bacteria of their main food source.

3. Chronic stress

The gut-brain axis is bidirectional. Prolonged stress raises cortisol, which suppresses the intestinal immune response and increases permeability. The gut reacts to stress just like the brain — and registers it with the same intensity.

4. Antibiotics and anti-inflammatory use

Broad-spectrum antibiotics eliminate pathogenic bacteria but also devastate beneficial flora. Non-steroidal anti-inflammatory drugs (ibuprofen, aspirin) used chronically directly damage the intestinal mucosa.

5. Alcohol and tobacco

Alcohol alters microbiota composition and increases intestinal permeability even with moderate consumption. Tobacco has a similar effect on the intestinal epithelium.

6. Infections and gastroenteritis

An acute gastroenteritis episode can trigger persistent changes in microbiota and intestinal permeability that remain months after apparent recovery.

Microbiota as the key to the intestinal barrier

The intestinal barrier isn't just epithelium: it's an ecosystem. Gut microbiota plays an active and essential role in maintaining permeability:

Butyrate-producing bacteria (Faecalibacterium prausnitzii, Roseburia, Eubacterium rectale) are the main fuel for epithelial cells. Without butyrate, the epithelium deteriorates and tight junctions fail.

The mucus layer protecting the intestine is manufactured and maintained by the microbiota. Akkermansia muciniphila is the most important bacterium in this process — its deficit is directly associated with greater permeability.

Beneficial bacteria regulate the expression of tight junction proteins (occludin, claudin, zonula occludens) that keep the barrier sealed.

A study published in Gut (2021) found that patients with greater intestinal permeability consistently had lower levels of Faecalibacterium prausnitzii and Akkermansia muciniphila — two of the most important markers of gut health.

If you're considering taking a microbiota test, our comparison of tests available in Spain can help.

What science says about leaky gut

A study published in Frontiers in Immunology (2017) established the mechanistic connection between dysbiosis, increased permeability, and systemic immune activation. The authors described how bacterial LPS fragments (lipopolysaccharide) that cross the damaged barrier activate TLR4 receptors, triggering chronic low-grade inflammation.

Researchers at Maastricht University developed the first validated biomarker of intestinal permeability (the lactulose/mannitol ratio), opening the door to systematic clinical evaluation.

A 2023 meta-analysis published in Clinical Nutrition concluded that microbiota interventions — especially using specific probiotic strains (Lactobacillus rhamnosus, Bifidobacterium longum) and fiber-rich diets — significantly reduce intestinal permeability markers in controlled trials.

How to know if you have leaky gut

Symptoms point the way but don't confirm it. The only way to know for certain what's happening in your gut is to analyze it.

GenBiome's VitalOme test identifies through high-precision NGS sequencing:

• Levels of Akkermansia muciniphila and butyrate-producing bacteria — the key guardians of the intestinal barrier
• The degree of dysbiosis and microbial diversity
• The presence of pro-inflammatory bacteria associated with greater permeability
• Specific imbalances with personalized dietary recommendations to restore the barrier

Knowing exactly which bacteria you have — and which you're missing — is the foundation for any effective gut recovery strategy.

6 steps to improve the intestinal barrier

While you wait or complement the analysis, these changes have solid evidence to restore the barrier and rebalance your microbiota:

1. 1Eliminate the main aggressors — Refined sugar, industrial emulsifiers, alcohol, and ultra-processed foods are the main barrier damagers. Drastically reducing them in the first 4-6 weeks gives the intestinal mucosa space to recover.
2. 2Increase fermentable fiber — Prebiotic fiber (inulin, FOS, pectin) feeds butyrate-producing bacteria. Sources: chicory, Jerusalem artichoke, garlic, leek, apple with skin, oats. Without fiber, Faecalibacterium prausnitzii and its allies can't produce the butyrate the gut needs.
3. 3Boost Akkermansia with polyphenols — Polyphenols from green tea, pure cocoa, blueberries, and extra virgin olive oil favor the growth of Akkermansia muciniphila. This bacterium is the main builder of the mucus layer.
4. 4Add fermented foods — Kefir, natural yogurt with live cultures, sauerkraut, and kimchi provide live bacteria that restore diversity and compete with pathogens.
5. 5Actively manage stress — Stress reduction practices (meditation, diaphragmatic breathing, moderate exercise) lower cortisol and directly reduce permeability.
6. 6Sleep enough with regular schedules — Sleep deprivation increases intestinal permeability within 24-48 hours. Maintaining regular sleep schedules is one of the most underutilized interventions for gut health.

When to see a doctor

Leaky gut can be associated with inflammatory bowel diseases (Crohn's, ulcerative colitis), celiac disease, type 1 diabetes, or rheumatoid arthritis. See your doctor if:

• Symptoms are severe or progressively worsening
• You have involuntary weight loss or blood in stools
• Joint or skin symptoms are intense
• You suspect celiac disease (reaction to gluten)

Microbiota analysis is a complementary tool to medical evaluation, not a diagnosis.

Conclusion

Leaky gut isn't a trend or an invented diagnosis — it's a physiological mechanism documented with decades of research behind it. And its most frequent and most treatable cause is gut dysbiosis.

If your intestinal barrier is compromised, no miracle supplement will restore it without first knowing what's happening in your microbiota. The first step is always the same: know your inner ecosystem to act with real data about your own body.

Article reviewed by the GenBiome scientific team. Last updated: September 2026.