There is no single symptom or widely accepted clinical test that definitively tells you whether you have a “leaky gut.” Increased intestinal permeability is a real, measurable biological phenomenon, but it is not yet recognized as a standalone diagnosis by major gastroenterology organizations. That said, specific patterns of symptoms, risk factors, and emerging lab tests can help you and your doctor figure out whether your intestinal barrier is compromised and what to do about it.
What “Leaky Gut” Actually Means
Your intestinal lining is a single layer of cells held together by structures called tight junctions. These junctions act like selective gates: they let nutrients through while keeping bacteria, toxins, and undigested food particles inside the gut. When those gates loosen, the lining becomes more permeable than it should be, and substances that normally stay contained can slip into the bloodstream.
One key player in this process is a protein called zonulin, which directly regulates how tight those junctions are. When zonulin is overproduced, the gaps between intestinal cells widen. This has been linked to autoimmune conditions like celiac disease and type 1 diabetes. At the same time, fragments of bacterial cell walls (called lipopolysaccharides, or LPS) can cross through a compromised barrier and trigger an immune response. Once in the bloodstream, these fragments activate inflammatory signaling throughout the body, leading to chronic, low-grade inflammation that may contribute to a surprisingly wide range of health problems.
Symptoms That May Point to Barrier Dysfunction
Here’s the tricky part: increased intestinal permeability doesn’t produce a unique set of symptoms. According to Cleveland Clinic, there are no symptoms directly caused by the permeability itself. Instead, the symptoms you notice come from the underlying damage to the intestinal lining or from the inflammation that follows when unwanted substances enter your bloodstream.
Digestive symptoms that often accompany barrier dysfunction include:
- A burning sensation in your gut, similar to an ulcer
- Painful indigestion, from erosion of the protective mucus layer
- Bloating, gas, diarrhea, or constipation
- Abdominal pain, particularly after eating
The systemic symptoms are what catch many people off guard. Chronic low-grade inflammation from a compromised barrier has been associated with obesity, type 2 diabetes, arthritis, chronic fatigue syndrome, fibromyalgia, and asthma. If you’re dealing with persistent fatigue, joint pain, skin issues, or brain fog alongside digestive problems, it’s reasonable to wonder whether your gut barrier is involved. But these symptoms overlap heavily with dozens of other conditions, which is exactly why “leaky gut” is so difficult to pin down on its own.
Common Causes and Risk Factors
If several of these risk factors apply to you, the likelihood that your intestinal barrier is compromised goes up.
Regular use of nonsteroidal anti-inflammatory drugs (like ibuprofen or naproxen) is one of the most well-documented causes. NSAIDs damage the gut lining directly and alter the composition of gut bacteria, both of which increase permeability. This damage can occur with both short-term and long-term use, and it affects the small intestine as well as the stomach. Symptoms of NSAID-related gut injury include nausea, indigestion, diarrhea, constipation, and abdominal pain.
Other established contributors include heavy alcohol consumption, chronic stress, a diet high in processed foods and low in fiber, infections, and existing inflammatory conditions like Crohn’s disease or celiac disease. Anything that disrupts the balance of bacteria in your gut can also play a role, since beneficial bacteria help maintain the integrity of the intestinal lining.
Tests That Measure Intestinal Permeability
The most established research test is the lactulose-mannitol ratio test. You drink a solution containing two sugars: lactulose (a larger molecule) and mannitol (a smaller one). A healthy gut absorbs mannitol easily but blocks most of the lactulose. You then collect urine for six hours. If more lactulose than expected makes it through, the ratio between the two sugars will be elevated, indicating that your intestinal barrier is letting larger molecules pass. A ratio below 0.05 is generally considered normal. Values above that threshold suggest increased permeability.
Blood tests measuring zonulin levels are also available, though interpreting them is less straightforward. In one study of apparently healthy people, the average serum zonulin level was around 34 ng/mL, but a larger study of over 360 participants found a median closer to 54.5 ng/mL. There is no universally agreed-upon cutoff for what counts as “too high.” Higher zonulin levels have been associated with larger waist circumference, elevated blood sugar, and abnormal cholesterol, but the clinical meaning of a single zonulin reading is still debated.
Some functional medicine practitioners also use tests for LPS antibodies or other inflammatory markers as indirect evidence of barrier dysfunction. These can provide useful clues but aren’t definitive on their own.
Why Getting a Clear Diagnosis Is Difficult
The biggest obstacle is that mainstream medicine doesn’t currently recognize “leaky gut syndrome” as a formal diagnosis. Increased intestinal permeability is acknowledged as a feature of many diseases, but there’s no consensus on when permeability alone qualifies as the problem versus being a consequence of something else.
The overlap with irritable bowel syndrome (IBS) is a good example of this challenge. Some studies have found that people with diarrhea-predominant IBS have measurably increased permeability in both the small and large intestines compared to healthy individuals. But other studies found no significant difference. When researchers examine gut tissue from IBS patients under a microscope, there are typically no visible signs of inflammation. As Monash University’s FODMAP research team has noted, current methods of measuring intestinal barrier dysfunction are suboptimal, and whether barrier changes are a cause of IBS or a consequence of it remains an open question.
This means that if you go to a gastroenterologist describing symptoms you believe are caused by leaky gut, you may be evaluated for IBS, celiac disease, inflammatory bowel disease, food intolerances, or small intestinal bacterial overgrowth instead. That’s not necessarily a bad thing. These conditions are treatable, and identifying them may resolve the permeability issue along the way.
What You Can Do Right Now
Even without a definitive test result, addressing the most common drivers of intestinal permeability is a practical starting point. If you use NSAIDs regularly, reducing or eliminating them (with your doctor’s guidance for managing pain another way) removes one of the strongest known triggers. Cutting back on alcohol, managing stress, and improving sleep all support barrier repair.
Dietary changes that emphasize whole foods, fiber, fermented foods, and omega-3 fatty acids can help restore a healthier balance of gut bacteria, which in turn supports the integrity of the intestinal lining. Eliminating foods you suspect you’re reacting to, such as gluten or dairy, for a few weeks and then reintroducing them one at a time can help you identify personal triggers.
If your symptoms are persistent, worsening, or accompanied by unexplained weight loss, blood in your stool, or significant fatigue, those patterns warrant a medical workup. A gastroenterologist can rule out conditions that require specific treatment while also evaluating whether increased permeability is part of the picture. The science on intestinal barrier dysfunction is evolving quickly, and the gap between what researchers know and what’s available in routine clinical practice is narrowing.