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You Probably Don’t Have a Leaky Gut

Leaky gut syndrome is not a real diagnosis, but if you step through the looking-glass like Alice in Wonderland, it will become real

There is a world in which our gut is leaking and causing all manner of diseases. It is not our world, but the trip through the looking-glass is an easy one to make.

In her 2023 book Doppelganger, Canadian author Naomi Klein, often confused with conspiracy theorist Naomi Wolf, uses the concept of the Mirror World to describe the alternate reality in which many people seem to live these days. In the Mirror World, our reality’s reflection gets distorted. Two Apple employees sitting in a restaurant and discussing the Apple Watch’s “Time Travel”, a since-abandoned feature allowing you to scroll through upcoming events and weather forecasts on your smart watch, becomes an overheard conversation about vaccine nanoparticles that let you travel back in time (true story). Everything gets misinterpreted in the Mirror World in the service of paranoia, distrust, and magical thinking.

There is a kernel of truth to the leaky gut theory, but what you’re likely to see online is its warped, outsized funhouse-mirror twin.

The lactulose-mannitol test

In the Mirror World, leaky gut syndrome is an epidemic. Seemingly every possible disease is actually a symptomatic manifestation of an intestine that has been turned into a sieve. The causes are many: foods that trigger inflammation, fluoride in the water, chronic stress, even genetically modified organisms. “Conventional medicine,” of course, does not recognize this syndrome, so patients seeking real understanding need to find alternative therapists. These unconventional healers promising cures and selling books about fake conditions cloak themselves in the garbs of science, accessorizing their names with impressive-sounding credentials and their articles with tags like “science based.” They look like legitimate ports in a storm because they reflect what we are accustomed to.

Infectious disease specialist Mark Crislip once wrote about the limitations of medicine, “I can’t just make up a disease or a therapy.” But in the Mirror World, you can.

Leaky gut syndrome is not a medical diagnosis, although some conditions do exhibit changes in what has been called “intestinal permeability.” The Mirror World can grossly oversimplify what is happening in the digestive tract, boiling it down to holes in the membrane separating the food we are digesting from our blood. The toxins of modern life pass through these holes, poison our blood, and cause illness, we hear.

When we step back from the looking-glass, however, we realize that the intestinal barrier is much more complex and ingenious. As food makes its way from our stomach to our small intestine and then our colon, it is broken down into smaller pieces, many of which need to go through the skin of this long tube in order to get to our blood and feed our cells. In essence, our food has to step through its own looking-glass. Thus, the lining of both our small and large intestines is already permeable to a degree, and this barrier is massive: it covers about 400 m2 in total (twice the area of a singles tennis court) and uses up about 40%—so close to half—of our body’s energy.

As we zoom in to the inside of our intestines, we can see multiple layers forming a barrier. Juices produced by our stomach, pancreas and liver serve to break down bacteria that could harm us. A thick coating of mucus acts as a gloopy barrier in case any surviving bacteria wanted to go through the actual intestinal lining. And then there are the cells forming this lining, like rowhouses, with channels like alleyways to allow nutrients through and immune cells to patrol the neighbourhood and attack invaders. It’s a far cry from a simple membrane that is either intact or full of holes.

In the Mirror World, leaky gut can simply be diagnosed based on symptoms, but there is also a test that can be done. It consists in drinking a solution of sugars (often mannitol and lactulose) and collecting the urine for a few hours after that. The idea is that mannitol, a small sugar, can naturally pass through the intestinal lining and into the blood, which will get filtered and the waste will form urine. Since mannitol is not used by the body, it will be peed out. Lactulose, however, is a bigger molecule and it will not easily get absorbed through the intestine… unless your gut is leaky, in which case lactulose will be found in the urine. The ratio of mannitol to lactulose measured in the urine becomes an indicator of a leaky gut.

In reality, academics who study intestinal permeability have criticized this test for lacking specificity and having limited validity. It’s just not a good test. But the basic idea of a leaky gut does have some legitimacy, even on our side of the mirror.

An occasional consequence but not a cause

Scientists don’t call it “leaky gut” but there is such a thing as “abnormal intestinal barrier function.” It means that this layered barrier is not doing an optimal job and is letting some things through that it shouldn’t. We know this happens in conditions that affect the gut and that are characterized by inflammation and ulceration. Inflammatory bowel disease or IBD is probably the best example. It encompasses a few conditions such as Crohn’s disease and ulcerative colitis. But this type of leaky gut is also seen in people with celiac disease (i.e. an allergy to gluten), intestinal infections, HIV/AIDS, and even irritable bowel syndrome (IBS) to a lesser degree.

The evidence we have in these specific cases argues for the existence of a leaky gut. Does this leakiness cause IBD? Unlikely. Is it a consequence of it or a by-product of what happens to a body struggling with IBD? Quite possibly.

On the other side of the mirror, however, this leaky gut is an octopus with a tentacle in every possible disease and unwanted condition. We are told it causes Parkinson’s disease, multiple sclerosis, cancer, allergies, depression, obesity, even autism. I have seen the association between autism and leaky gut be attributed to the disgraced Andrew Wakefield, who jumpstarted the modern anti-vaccine movement with his now-retracted paper on the measles-mumps-rubella vaccine, but it actually predates him. I have traced it back to a 1996 Italian paper in which 21 autistic children were tested using the unreliable lactulose-mannitol test. Wakefield cites this paper in his now-infamous 1998 study which, few people seem to remember, actually focused not only on autism but on inflamed and dysfunctional intestines. Since then, we have good evidence that autistic children do not have leaky guts, and there is no good scientific evidence that a gluten-free and casein-free diet, linked to this idea of a leaky gut, alters the course of autism.

The idea that a leaky gut is even present in all of the conditions listed in the previous paragraph is based on very limited or simply non-existent data. It is born out of feelings not facts. Some people wish it so, and thus it becomes real in the Mirror World. But when we actually look at the scientific evidence and not uncontrolled testimonials, we see many arguments against a leaky gut being the dastardly villain naturopaths often wish it to be. In laboratory animals which have a genetic error that renders their intestinal barrier leaky, we do not see disease as a consequence. This further points in the direction of the leakiness following disease, not causing it. There is also no good evidence that an intervention to restore this intestinal barrier alters the course of disease. There are variables that are known to increase leakiness: drinking alcohol, for instance, can directly damage intestinal cells and alter their tight junctions, allowing more molecules through. On the flip side, a diet high in fibre, vitamin D, glutamine (an amino acid found in protein), and short-chain fatty acids (produced when we digest the fibre found in fruits, vegetables, and legumes) can improve the barrier.

The twist is that reducing alcohol intake and choosing a healthy diet are tips that everyone can benefit from, leaky gut or not. Online, though, you will be told to follow the four (or sometimes five) Rs to patch up your gut, and no, they don’t mean reduce, reuse, and recycle. They mean remove all so-called inflammatory food, which includes gluten, dairy, corn, soy, sugar, eggs, caffeine and alcohol (a dangerously restrictive diet that is unwarranted and shouldn’t be attempted without consulting with a registered dietitian); replace the bad foods with dietary supplements to support your digestive system (even though supplements are not needed and are often contaminated with dangerous substances); reinoculate your gut with good bacteria by taking probiotic supplements (which are unlikely to work, as interventions targeting gut bacteria are mostly hype at this point); and repair your gut by taking even more supplements. Some will also mention rebalance, as in improving your life to better support your health, but this is the kind of non-specific advice that we can all benefit from.

When doing research for this article, I ended up communicating with the head of an association which used to have a webpage dedicated to criticizing the bad science surrounding leaky gut syndrome. I was told this single article of theirs, since taken down, generated “regular death threats.” Not angry emails, and not occasional ones. Death threats. Plural and periodic. This is what unfortunately can happen in the Mirror World: radicalization. Faced with chronic symptoms that are dismissed by physicians (often unjustly), frustrated people turn to Jabberwocky doctors through the looking-glass: naturopaths, integrative physicians, and so-called functional medicine practitioners who cast doubts on medicine as a whole and offer their reassuring diagnoses and suitcases full of supplements. Patients begin to identify with their catch-all Mirror-World diagnoses, like leaky gut syndrome, adrenal fatigue, and chiropractic subluxations. They meet others like them, and these communities provide much-needed comfort and a space to commiserate. When the medical establishment dismisses their diagnosis, these patients, who may have come to see all of medicine as corrupt and conspiratorial, push back with anger.

In Doppelganger, Naomi Klein summarizes the thoughts of a psychoanalyst, Sally Weintrobe, on how to build a more caring society. “If we want more people,” Klein writes, “to make better choices—not to shop for useless stuff as a source of solace, not to spread disinformation for clicks and clout, not to see other people’s vulnerability and need as a threat to our own interests—we need better structures and systems.”

Our healthcare system needs to be less leaky if we want to rein in false diagnoses like leaky gut syndrome.

Take-home message:
- Leaky gut syndrome is not a medically accepted diagnosis, yet it is common in integrative medicine, naturopathy, and functional medicine
- Changes to the permeability of the intestine have been noted in inflammatory bowel disease, gut infections, HIV/AIDS, even IBS, but they appear to be consequences of these conditions and not their cause
- The lactulose-mannitol test sometimes used to diagnose leaky gut syndrome is not reliable, and the dietary supplements often prescribed to treat the syndrome are not based on good scientific evidence


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