Finding The Leak: Part 2 – Can You Patch A ‘Leaky Gut’?

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As we saw in the previous instalment, ‘leaky gut syndrome’ is not a real syndrome. It’s a characteristic of certain diseases, but not necessarily a cause – there’s no good evidence that increased gut permeability is a significant contributor to things like IBD, obesity and diabetes.

That said, gut permeability does vary from person to person, and elevated gut permeability is unlikely to be a good thing. Many online sources point to specific causes of increased gut permeability such as lectins and gluten, while advising that gut permeability can be reduced through diet. In this article, we’re going to scrutinise some of this advice and whether it is actually backed up by science.

Disclaimer: Nothing in this article is health advice. You should consult with your doctor if you experience persistent gastrointestinal symptoms.

Why High Gut Permeability Might Be Bad

If molecules from food and pieces of bacteria are able to make their way from the gut into the bloodstream, even in very small quantities, this is likely to trigger low levels of chronic inflammation. White blood cells recognise molecules that shouldn’t be there, resulting in the release of inflammatory signals with the purpose of aiding the removal of any potential pathogens. Unfortunately, if said molecules are continuously leaking into the blood, then these inflammatory signals will never stop, resulting in chronic inflammation. 

Chronic inflammation is bad news, slowly inflicting widespread damage throughout many tissues and organs. It’s thought to be one of many drivers of age-related diseases and age-related deterioration in general. However, it’s important to stress that there are many factors contributing to chronic inflammation besides gut permeability, most of which are largely unavoidable. The relative importance of gut permeability when it comes to chronic inflammation and ageing isn’t well understood – it’s just one of a long list of suspects.

What Causes Elevated Gut Permeability?

If we suspect that high gut permeability might be bad, the natural next step is to ask how we can avoid it and what we can do to reverse it. Let’s start with the first question. We will go through the most commonly cited culprits and address the supporting science or lack thereof.

Poor diet: Diet is a core pillar of health and it is often cited as a determinant of gut permeability. Diet certainly has a significant impact on gut health and on the composition of the gut microbiome, which in turn can influence gut permeability. However, diet is a complex topic to study and the experimental evidence that it affects gut permeability isn’t as strong as you might expect, but we’ll get to that when we discuss how ‘leaky gut’ can be reversed.

Exercise: Several small studies appear to show that high intensity exercise (most commonly between 50% to 70% of maximum capacity) for 30 minutes or more led to a short-term increase in gut permeability. However, moderate intensity exercise does not appear to have this effect, and if anything improves gut function and reduces permeability.

Lectins: Lectins are molecules found in most plants, especially legumes. They’re carbohydrate-binding molecules which, as you might guess, means that they attach themselves to carbohydrates. This can prevent their absorption by the gut and so lectins are sometimes described as ‘antinutrients’. However, they may also bind to carbohydrate molecules present within human cells, making certain lectins (emphasis on ‘certain’) toxic. 

Some studies have fed raw legumes to rats or pigs and found that lectins could bind to carbohydrates in the cells lining the intestine, disrupting the intestinal barrier and leading to increased permeability. There are also instances in which foods with abnormally high lectin concentration have made humans ill. However, soaking and boiling eliminates almost all lectin activity from many foods, though there are some lectins that are very resistant to heat degradation.

When actually looking at human data, however, there’s really no good evidence that lectin-rich foods increase gut permeability. If anything, plant-based diets (and legumes especially) appear to be beneficial for overall gut health due to their high fibre content, so reducing one’s intake doesn’t make a lot of sense. Just be sure to boil them first. The WHO recommends that dried beans be soaked for 12 hours and boiled for 10 minutes. Tinned beans have already undergone this process.

Gluten: As discussed in the previous instalment, increased intestinal permeability is a key characteristic of inflammatory bowel diseases like coeliac disease, in which gluten triggers flare-ups. However, some people without coeliac disease have a poorly understood condition termed non-coeliac gluten sensitivity, in which they react negatively to gluten-containing foods. There is some evidence that gut permeability may be increased by gluten in such individuals. 

The situation in people without coeliac disease or gluten sensitivity is less clear. Gluten can activate zonulin, a molecule that regulates tight junctions – those structures that control what can and can’t slip between cells in the lining of the intestine). However, nearly all of the human evidence comes from people with coeliac disease or self-reported gluten sensitivity, so it’s impossible to say whether gluten increases intestinal permeability in the majority of people.

Artificial sweeteners: There’s growing evidence that artificial sweeteners may not be that much better than sugar when it comes to gut health. Some artificial sweeteners harm the microbiome, which plays a role in regulating gut permeability. Some studies have linked artificial sweeteners directly to gut permeability – for example, this study in isolated intestinal cells found that sweet taste receptors (yes, your gut can taste things – read here to learn more) can disrupt tight junctions when activated by common sweeteners like sucralose and aspartame. However, whether this actually happens and whether it matters in the guts of living humans is unclear.

Stress: Stress hormones can in theory affect gut permeability, but evidence from human studies is mixed. This may be because the kinds of stress experienced by animals in animal studies are difficult to replicate on humans in a laboratory environment. More research is needed, but for the moment it’s hard to draw any conclusions about the effects of psychological stress on healthy humans.

Drug overuse: Overuse of alcohol or long-term use of NSAID painkillers (which include aspirin and ibuprofen) can result in increased intestinal permeability.

Patching The Leak

Now that we have covered some of the main potential contributors to gut permeability, it’s time to ask what we can do about it.

The most common (and arguably most reasonable) advice is that certain diets and probiotic supplements can prevent or reverse high permeability. We know that the bacteria in our guts play an important role in regulating gut permeability and that diet is essential for nurturing these bacteria, so this advice sounds plausible. However, you may be surprised to learn that the scientific evidence is not particularly supportive of this assertion. In a recent systematic review earlier this year, researchers identified just 12 eligible randomised, double blind placebo-controlled trials investigating the effects of specific dietary components on intestinal permeability in healthy people. 

They found moderate certainty evidence that probiotics as well as the prebiotic inulin decreased intestinal permeability. Probiotics are live bacteria from strains thought to be beneficial for human health. They digest compounds that our guts can’t, outcompete pathogens, and produce signalling molecules that can influence inflammation, tight junctions and mucous production. It makes sense that probiotics might have an effect on intestinal permeability. The same goes for prebiotics, which are those non-digestible compounds like inulin that feed out gut bacteria. 

They also found very low certainty evidence that fructose (a form of sugar that is two glucose molecules joined together) may increase permeability. Based on a mix of test tube animal and human studies, there are a number of reasons why fructose might increase permeability, including increased inflammation, disruption of the microbiome and disruption of tight junctions. However, that systematic review of diet and gut permeability ultimately concluded that, due to the scarcity of research, ‘There was no strong evidence that diet or dietary interventions increase or decrease intestinal barrier permeability in healthy individuals.’

A lot of the more general dietary recommendations you will find online when it comes to ‘treating’ a leaky gut (eat a plant-based diet rich in fibre and fermented foods, avoid artificial sweeteners and so on) are sound advice for general gut health, but have little if any evidence to actually show that these diets reduce permeability in a controlled experiment.

Other recommendations are just plain nonsensical, such as ‘colon cleanses’ (more likely to disrupt the gut microbiome than anything else) and eating mostly raw food to restore the balance of gut enzymes (there’s no proof this works).

The Take Home Message

The idea that certain diets, specific dietary compounds or lifestyle practices can alter gut permeability is scientifically plausible. However, when thinking about general health and wellbeing, we should be focussed on what actually matters: a) Do lifestyle modifications demonstrably reduce gut permeability and b) Does this translate to actual health benefits? At the moment, the answer to both of these questions is a definite ‘maybe’. 

Many people who experience symptoms attributed to ‘leaky gut’ try the advised lifestyle modifications and find that their symptoms improve. However, this does not mean that intestinal permeability was their problem. And when so many of the proposed remedies are just good practice for gut health in general, one has to wonder if the concept of ‘leaky gut’ is worth thinking about for the average person who just wants to improve their health and wellbeing. On the one hand, it may motivate people to make positive changes to their lifestyle. On the other, it can be used as a marketing strategy to sell products that may or may not actually address gut permeability, or worse, cause people to delay seeking medical advice because they believe their symptoms to be caused by ‘leaky gut’.