Intestinal Permeability and “Leaky Gut” Testing

An honest account of what leaky gut testing can and cannot tell you — and what we check first when gut symptoms are real but the standard tests came back normal.

What intestinal permeability actually is

The gut lining is a selective barrier. It absorbs nutrients while keeping bacteria and partially digested food out of the bloodstream, and the junctions between the cells open and close to control this. Intestinal permeability describes how open that barrier is.

This is a real, well-described phenomenon. Increased permeability is documented in coeliac disease, inflammatory bowel disease, serious infection and heavy alcohol use. The science is genuine, and it is an active research field.

Where the evidence stops

What has not been established is the step commercial testing depends on: that measuring permeability in a person with everyday digestive symptoms produces a number you can act on, or that changing it improves how they feel.

The commonly sold marker is zonulin. Several widely used zonulin assays have been shown not to measure zonulin reliably, and results vary between laboratories. Lactulose-mannitol urine testing is better validated as a research tool but is affected by kidney function, gut transit time and what you ate beforehand, and there is no agreed threshold that separates “normal” from “needs treatment” in an otherwise healthy person.

We do offer intestinal permeability testing, using the lactulose–mannitol method rather than zonulin. Given the limits above, we suggest it only after the more common causes below have been checked, and we explain what it can and cannot show before you book. A result on its own does not diagnose a condition. This sits alongside our wider position in Functional Lab Testing: What Is Evidence-Based and What Is Not.

Your symptoms are still real

Bloating, irregular bowels, discomfort after eating and fatigue are common and genuinely disruptive. Saying that a particular test is unreliable is not the same as saying nothing is wrong. It usually means the answer is somewhere more ordinary — and more treatable.

What we look at instead

  • Coeliac screening — tissue transglutaminase antibodies with total IgA. Coeliac disease is underdiagnosed and genuinely causes increased permeability. It must be tested while still eating gluten.
  • Inflammation and blood count — hs-CRP, full blood count and ferritin. Iron deficiency with gut symptoms needs explaining, not supplementing.
  • Thyroid and metabolic markers — both alter gut motility and are easily missed.
  • Faecal calprotectin — separates inflammatory bowel disease from irritable bowel syndrome, and is a genuinely useful test.
  • A proper dietary assessment — most bloating traces back to fermentable carbohydrates, lactose, eating pattern or fibre load. A structured elimination and reintroduction, supervised so the diet does not narrow permanently, identifies triggers more reliably than any panel.
  • True food allergy, where the pattern fits — see our allergy testing and the difference between allergy and intolerance.

When to see a doctor rather than book a screening

Some symptoms need medical assessment first, not a nutrition plan: blood in the stool, unintentional weight loss, difficulty swallowing, persistent vomiting, a change in bowel habit lasting more than six weeks over the age of 45, or a family history of bowel cancer or inflammatory bowel disease. Please see a doctor about those promptly.

Talk it through first

If you have been offered a leaky gut test elsewhere, or you have a result you are unsure about, message us on WhatsApp before you spend anything. We will tell you honestly whether testing will change the plan — and often it will not.

HDC Medical, Unit 3A-08 Oval Damansara, 685 Jalan Damansara, 60000 Kuala Lumpur. Appointment only. See our screening packages for what is included.

This article is for general education and does not replace individual medical advice. Persistent or alarming digestive symptoms should be assessed by a doctor.