leaky gut: the full lowdown

Written by Dr. Jenna Macciochi

We have developed a very complicated and highly specialised digestive system. Our digestive tract is delicate, a fragile barrier that is just one cell thick! This anatomical set-up is deliberate, maximising digestion and the absorption of nutrients from our food. Although we think of our digestive tract as inside us, it actually forms the largest interface of our body with the outside world. As you can imagine, it’s a constant challenge to keep this delicate barrier in order.  

The gut is also the home to our microbiota – a collection of trillions of microbes that live within us.  Our microbiota not only help us digest our food but are key teachers and educators of our immune system (as I’ve written about it here, here and here).  Variations in these gut microbial populations are now associated with the development of several diseases related to immune dysfunction. So gut health doesn’t just stay in the gut, but it’s critical to our overall health and wellbeing. 

The Gut Firewall

The delicate cells that line our gut keep this barrier tight much like a mucosal ‘firewall’. Your gut works hard to both absorb nutrients whilst keeping out undigested food and potentially harmful things we might end up swallowing. Our microbiota rest atop this barrier which acts as a gatekeeper, preventing these helpful gut microbiota from getting into places they shouldn’t (we  consider these  “good bacteria” but only while they stay in their rightful place).

Gut Leaky?

But sometimes the gut has to get “leaky” (aka, permeable). Yes, leaky gut is a real thing, but perhaps not as Dr. Google would have you believe. We all have some degree of leaky gut, as this barrier is not completely impenetrable (and isn’t supposed to be!). When we eat a meal, our gut becomes more leaky which helps us absorb nutrients. In science speak we call this “intestinal permeability” (1).  The spaces in between our gut barrier cells get bigger making it easier for our good bacteria (and anything else inside our digestive system) to cross out of the gut and go trespassing around the body via our bloodstream.

Our immune cells all over the body are then presented with bits of food and bacteria, which contain immune triggering barcodes – when scanned by immune cells, inflammation is switched on (this happens when they end up out of their gut domain).  This happens to a tiny degree each time we eat: up to four hours after a meal, trespassing contents of our gut flow through the body, triggering the immune system to elicit transient inflammation.  In healthy people with a diverse microbiota (who are regularly eating a varied and fibre-rich diet) post-prandial epithelial permeability (what happens after we eat) is mild and short-lived, not causing any issues. And since leaky gut can be normal, your body has all sorts of checks and balances in place to ensure occasional leakiness does not become a problem. If leaky gut is somewhat normal, can it ever be problematic?  

Leaky gut and health

The idea of a leaky gut leading to chronic inflammation and kick-starting or exacerbating both physical and mental health conditions is an exciting one for medical science. But is it true? From fatigue, food sensitivities, joint pain, moodiness, irritability, sleeplessness, autism, and skin problems, like eczema and psoriasis, proponents of leaky gut syndrome claim it’s the underlying cause of most modern health problems. Well, as is often the case with sensational health headlines, there is a hint of truth behind the claims. 

Cause or correlation?

It’s true, we do see increased intestinal permeability in certain diseases (2).  There can be increased gut leakiness in those with inflammatory gut conditions including celiac disease, Crohn’s disease and ulcerative colitis.  In the early 1970’s research emerged demonstrating that the degree of intestinal permeability correlates with the severity of coeliac disease (3). Studies have also found increased intestinal permeability in relatives of those with inflammatory bowel disease, who are at an increased risk of developing the disease. Since then, there have been plenty of scientific studies associating leaky gut with several chronic inflammatory diseases, specifically autoimmune disorders not only of the digestive tract, but also outside of the digestive tract including type 1 diabetes (4) and rheumatoid arthritis (5).

Some studies show that leaky gut may be associated with other chronic conditions including chronic fatigue syndrome, fibromyalgia, allergies, asthma, acne, obesity, and even mental illness (6, 7). 

Despite all these links, intestinal permeability remains a symptom of these ailments, most of which are caused by the perfect storm of a myriad of factors. So it’s difficult to prove that leaky gut is the cause, although it may well be an exacerbating component in certain cases. 

Tests and Treatment for Leaky Gut

The simple fact is the identification and diagnosis of intestinal permeability is difficult.  Currently there is no gold standard for measuring intestinal permeability. All tests available have limitations.  There is a test available that shows whether an individual has intestinal permeability. It works by measuring levels of two indigestible sugars, mannitol and lactulose, in the urine (8). But it’s not very reliable and doesn’t give a clear picture of gut leakiness, particularly in the lower bowel. and serum zonulin, the protein responsible for the disassembling of the gates between the cells lining our digestive tract.  But zonulin is released from many tissues including adipose tissue and proposed to be a biomarker of metabolic syndrome, obesity, inflammation and poor health more so than just a measurement of leaky gut (9). 

With limited tools available to accurately measure leaky gut you should be wary of treatments offered by people who claim to be able to “cure leaky gut syndrome”, as there is little scientific evidence to suggest they are beneficial for many of the conditions they are claimed to help. It’s doubtful they have been tested in randomised clinical trials, and they may even do more harm than good.  

What affects your gut leakiness?

Many ‘solutions’ that leaky gut syndrome proponents recommend are based on fad diets, which declare that normal foods cause serious gut problems in most people. The one thing that we do know is that bacteria in your gut microbiota play an enormous role as gatekeepers of gut integrity.  Having a diverse and healthy microbiota is crucial as is keeping these good germs well-fed (think fibre) to help reinforce the integrity of the gut barrier.  When our good gut microbes chow down on fibre they produce a veritable banquet of metabolites, many of which work hard to keep protect the gut barrier integrity and counter the ebbs and flows of post-prandial permeability (10). 

Some amino acids (the building blocks of protein) including glutamine and tryptophan have shown some promise in protecting and repairing the gut barrier in certain disease situations. Supplementation with glutamine heals the intestinal barrier in experimental models of inflammatory disease (11, 12) and getting these additional amino acids into their diets can help patients with inflammatory gut conditions (13, 14).  

Other dietary and lifestyle factors can impact gut leakiness in a negative way including (15, 16, 17, 18, 2) : 

• Obesity 
• Consistently snacking, grazing and overeating.  
• Eating a very large meal or a meal heavy in excessive fat (particularly saturated fat) or fructose (fruit sugar, in the absence of adequate fibre)  
• Hyperglycemia – prolonged high blood sugar – found in poorly controlled diabetes
• High cholesterol can also compromise the gut barrier 
• Nutrient deficiencies, specifically Vitamin A, D and zinc 
• High doses of vitamin C
• Certain drugs including aspirin or NSAIDs, antibiotics and the drugs used in chemotherapy
• Alcohol can also loosen up our barrier
• Normal processes such as the menstrual cycle, in the weeks from ovulation to menstruation
• Heavy exercise, particularly in hot climates, getting older and just feeling stressed
• Persistent acoustic stress from noise pollution

The bottom line

Unless you have celiac disease (then you need to practice strict gluten avoidance), a true food allergy or intolerance, or another condition that requires drastic dietary changes based on verified research, you should cast a critical eye over anything or anyone who suggest you embark on extreme exclusion diets under the guise of curing leaky gut.  It actually appears that digestive health symptoms such as bloating, abdominal cramps, pain, heartburn, reflux and nausea do not correlate with intestinal permeability (15). 

Also avoid untested and heavily marketed supplements, even if they claim to have a herbal or natural base. Talk to your doctor, a registered dietitian or nutritionist if you have more questions or concerns.

About the author

Immunologist Dr. Jenna Macciochi unravels the science underlying strong immunity and teaches us how to be well in a modern world. Currently a lecturer at the University of Sussex, she specialises in understanding how nutrition, lifestyle, and gut health interact with the immune system in health and disease. Jenna is a Brighton (UK) based mum to twins, a perpetual kitchen experimenter with a passion for movement and exercise.

References

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4. Vaarala, O., Atkinson, M. A. and Neu, J. (2008) ‘The “perfect storm” for type 1 diabetes: The complex interplay between intestinal microbiota, gut permeability, and mucosal immunity’, Diabetes. American Diabetes Association, pp. 2555–2562. doi: 10.2337/db08-0331.
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