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The term ‘Leaky Gut’ or ‘Intestinal permeability’ is often discussed within complementary health circles, as it is widely accepted by natural health practitioners that increased gut permeability is implicated in many different health conditions. It has been associated with numerous atopic conditions, inflammatory states, autoimmune conditions, skin conditions and many (often unexplained) abdominal symptoms. (To read more about probiotics, leaky gut and allergies, you may like to read Kerry's informative blog post.)

So what is ‘leaky gut’?

Leaky gut refers to an increase in permeability in the epithelial surface of the gut. The intestinal epithelia is our largest ‘barrier’ against the external environment. It protects us from toxins and pathogenic microbes that may enter the GI tract from either our food or the environment, however incredibly, this vital protective barrier is only one cell thick.

That's right, the intestinal barrier that separates the contents of the gut from our systemic circulation (or blood stream) is only one cell thick! It extends from the esophagus to the anus, and this single cell layer plays the vital role of selecting and screening what is taken in to the general circulation from the gut lumen, and what is excluded.

The intestinal epithelia allows some molecules to pass through, but prevents others

In order to allow certain molecules through in to the bloodstream, whilst blocking others from entering, the epithelia is what we refer to as a ‘selectively’ permeable barrier. When functioning correctly, it permits the entry of very small molecules of beneficial nutrients, electrolytes and water across its border, but prevents the entry of larger molecules of undigested foods or pathogens in to the bloodstream.

This passage of nutrients occurs in two ways, either directly through the epithelial cells themselves (transcellular transport) or through structures known as the ‘tight junctions’, located between each pair of neighbouring epithelial cells (paracellular transport). Up until fairly recently, not too much was known about the workings of the tight junctions, however, scientists have recently isolated a molecule called zonulin, which appears to be responsible for opening up the tight junctions. This is an essential process for nutrient absorption and does not always lead to leaky gut, however when we have too much zonulin, and these tight junctions are too open, too often, this can cause what is known as leaky gut.

To read more about this, you may like to read my earlier blog post, which looks specifically at zonulin, and its impacts on our health. I mentioned in this blog that scientists now know that zonulin is particularly over-produced in response to either gluten in the diet or to dysbiosis, both of which cause intestinal inflammation.

It leads us to the question that if dysbiosis can trigger an over-production of zonulin, and therefore cause leaky gut, could probiotics, play a part in healing it?

Can probiotics heal a leaky gut? A look at the research

Disappointingly, there have been relatively few human studies looking at the potential role of probiotics in reducing intestinal permeability. Most of the research to date has been performed using animal models, for example, In 1996, it was shown that the human probiotic strain Lactobacillus plantarum 299v and the rat-originating strain Lactobacillus reuteri R2LC could reduce intestinal permeability in a methotrexate-induced colitis model in rats.

Subsequently, many animal models have shown that Lactobacilli are able to counteract increased paracellular permeability bought on by factors such as: diet, chemicals, infections, or stress. It has also been demonstrated that Lactobacillus rhamnosus GG, is able to improve intestinal barrier function in rats who's tight junctions had previously been compromised by either rotavirus infection1 or exposure to cow's milk antigens2.

Due to such positive findings in animal studies, researchers are slowly starting to look at whether these results could be replicable in humans. One study demonstrated that short-term administration of the probiotic strain Lactobacillus plantarum WCSF1, given to healthy volunteers, could indeed positively influence the tight junctions between duodenal epithelial cells.

Probiotics shown to reduce intestinal permeability in children with atopic dermatitis

Even more encouragingly, in 2004 a Danish study3 looked at intestinal permeability in children with atopic dermatitis. 41 children took part in the study, and were asked to take a lactulose and mannitol test at the start and end of the study period. The lactulose and mannitol test is given to identify the degree of intestinal permeability in the study participants. The test works on the principle that small sugar-alcohol molecules (i.e. mannitol) are readily absorbed by the intestinal villi, whilst larger molecules such as disaccharides (i.e. lactulose) are not. These water soluble molecules are not metabolised by the body and are therefore just excreted through the urine, where they can be collected and studied. Under normal circumstances the ratio of lactulose to mannitol in the collected urine is low (i.e proving that lactulose is not absorbed but mannitol is). When ‘leaky gut’ is present however, the large sugar molecule can permeate the mucosa and is recovered in the urine in larger quantities. In this situation the level of lactulose is increased in the urine and therefore the ratio of lactulose to mannitol is high.

In between each test, the children were all given a two strain Lactobacillus supplement to take for six weeks. The supplement contained: Lactobacillus rhamnosus 19070-2 and Lactobacillus reuteri DSM 12246. The results of the lactulose and mannitol tests showed that the probiotic supplementation had indeed reduced the absorption of the larger disacchardide molecule of lactulose, which can only mean that the intestinal barrier function was improved. In addition, the children had a reduction in intestinal symptoms.

Moving forward

More research will need to be done before we can confidently say whether probiotics can be used therapeutically to help heal a leaky gut, however, the initial findings look promising. Given that our gut microbes are in constant communication with the immune system, and that we already know that they can influence cytokine production and therefore reduce intestinal inflammation, I would expect future scientific research to support the theory that probiotics can play a part in healing a leaky gut.

To read our in-depth blogs looking at how probiotics interact with our immune system, you may find the following posts interesting:

Probiotics for immunity - a look at the research

Head over to our Probiotics Learning Lab for Gut bacteria and allergies


1. E., Kaila, M., Arvola, T., Majamaa, H., Rantala, I., Virtanen, E. et al .Lactobacillus rhamnosus strain GG, ATCC 53103 (Lactobacillus GG), has been demonstrated to improve intestinal barrier function compromised by rotavirus infection17X17Isolauri, . Diet during rotavirus enteritis affects jejunal permeability to macromolecules in suckling rats.Pediatr Res. 1993; 33: 548–553

2. Isolauri, E., Majamaa, H., Arvola, T., Rantala, I., Virtanen, E., and Arvilommi, H.Lactobacillus casei strain GG reverses increased intestinal permeability induced by cow milk in suckling rats. Gastroenterology. 1993; 105: 1643–1650

3. Vibeke Rosenfeldt, MD, PhD Correspondence information about the author MD, PhD Vibeke Rosenfeldt Email the author MD, PhD Vibeke Rosenfeldt, Eva Benfeldt, MD, PhD, Niels Henrik Valerius, MD, DrMedSci, Anders Pærregaard, MD, DrMedSci, Kim Fleischer Michaelsen, MD, DrMedSci. Effect of probiotics on gastrointestinal symptoms and small intestinal permeability in children with atopic dermatitis. From the Department of Human Nutrition, The Royal Veterinary and Agricultural University, the University Clinic of Pediatrics, H:S Hvidovre Hospital, and the Department of Dermatology, University of Copenhagen, Gentofte Hospital, Copenhagen, Denmark

This FAQ has been answered by Kathy Wheddon, Nutritional Therapist DipION.