Finding The Leak: Part 1 – What Is ‘Leaky Gut Syndrome’ And Is It Real?

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Do you have bloating, diarrhoea, constipation, or indeed any gastrointestinal symptom at all? What about fatigue, headache and confusion? Skin rashes? Joint pain? Autism? According to some, you may have something called ‘leaky gut syndrome’, a condition in which the contents of the gut can pass through the lining of the intestine and into the bloodstream, causing all manner of problems.

Leaky gut syndrome is not recognised as a medical condition by health authorities like the UK’s NICE or the USA’s FDA. Websites focussing on health fraud and misconduct such as Quackwatch regard leaky gut syndrome as a ‘fad diagnosis’. The Wikipedia page for leaky gut syndrome is part of the alternative medicine series. And yet, you can find hundreds of articles in peer-reviewed scientific journals discussing the topic of ‘leaky gut’, as well as plenty of reputable health blogs like Harvard Health. It’s therefore not surprising that this topic is a source of confusion for many. In this article, we’re going to try to clear up some of this confusion, but first we need to establish some basic science.

Germs And Junctions: A Guide To Gut Permeability

There is a lot of material within our intestines at any one time. Some of that material is food, which needs to be broken down into nutrients that can then be absorbed by the lining of the gut so that it can pass into the bloodstream. However, there are a lot of molecules and microorganisms in the gut that are quite harmless or even beneficial so long as they stay there, but are really, really harmful (read fatal) when they get into the circulation.

Because of this, the lining of the intestines needs to be able to allow some molecules through while being a barrier to others. To achieve this, the epithelial cells that make up the lining of the intestines are packed closely together, and the gaps that would otherwise exist between neighbouring cells are plugged by structures called tight junctions.

Tight junctions allow the passage of small molecules like water, but prevent larger, potentially harmful molecules from squeezing in between the epithelial cells and into the blood. Instead, these molecules must be absorbed by the epithelial cells and then exit into the bloodstream on the other side. Since cell membranes are impermeable to most large molecules, there need to be specialised protein channels or pumps present within the cell membrane in order to allow such molecules through. In other words, a healthy gut has a good amount of control over which molecules are allowed to enter the bloodstream – this is known as selective permeability.

Unfortunately, the lining of the intestine is not always a perfect barrier to ‘unwanted’ molecules. There are some situations in which the gut might become generally more permeable – one might even say that it becomes a little bit ‘leaky’. Discussion of gut permeability as a variable that might affect health has become much more prevalent over the past decade or so, but there’s still a lot of uncertainty about whether it really matters and for whom. Let’s now take a closer look at some of the science to see if we can clarify what is and isn’t known.

Leaky Gut – A Hint Of Truth

Scientists have found that gut permeability is increased in some diseases, but the exact nature of this link is still being studied. Let’s start with what is known: people with inflammatory bowel disease have abnormally high gut permeability for various reasons. For example, multiple studies have documented that people with inflammatory bowel disease have abnormal tight junctions during flare-ups and thinner mucous layers covering the epithelial cells, which allow more molecules to first reach the epithelium and then slip between cells. Many research articles refer to this as a ‘leaky’ gut epithelium.

What is less clear is whether this increased gut permeability plays a role in the development of IBD in the first place, or whether it is simply a consequence of damage to the lining of the gut caused by inflammation. There’s some evidence for the former – for example, experiments in mice show that when gut permeability is increased (for example by deleting genes coding for tight junction proteins), the mice develop IBD-like conditions. Human studies have also found that 40% of close relatives of IBD patients have some altered intestinal permeability, opening up the possibility that there are genetic factors that increase gut permeability and might thereby predispose you to IBD. However, this is still an area of ongoing research and the idea that a ‘leaky gut’ contributes to IBD in a meaningful way should be considered speculation at this point.

‘Leaky Gut Syndrome’ – The Fine Line Between Fact And Fad

So, it seems as though a permeable or ‘leaky’ gut is associated with IBD. We also know that some people without IBD have a higher gut permeability than others, which is unlikely to be desirable. It’s not unreasonable to ask whether a higher gut permeability – even if you are otherwise healthy – might lead to a small leakage of inflammatory molecules into the blood, triggering low levels of chronic inflammation which we know is associated with many diseases, not just IBD. 

This leads us on to the increasingly popular concept of ‘leaky gut syndrome’, an elevated gut permeability in an otherwise healthy person that is characterised by various symptoms, and that can be cured through diet and probiotic supplements. Given all that has been said, why is this concept so controversial? Let’s address this idea piece by piece, starting with the first problem: the use of the word ‘syndrome’.

What’s In A Name?

An example of a clinician’s definition for the word ‘syndrome’ is ‘a recognizable complex of symptoms and physical findings which indicate a specific condition for which a direct cause is not necessarily understood.’ However, if you look at the typical symptoms listed for leaky gut syndrome (bloating, fatigue, and skin rashes to name only a few) they are anything but specific, and could indicate any number of diseases or no disease at all. ‘Leaky gut syndrome’ is not an officially recognised disease and so has no diagnostic criteria. While it might seem trivial on the surface, using the term ‘syndrome’ to describe a leaky gut is confusing at best and potentially harmful if someone attributes the symptoms of another disease to a leaky gut.

That doesn’t necessarily mean that some form of gut permeability condition doesn’t exist and will never be diagnosable. Just as we have set upper limits for blood pressure beyond which you are considered to have hypertension, clinicians may one day decide to diagnose ‘hyperpermeability’ based on objective measurements of gut permeability that do in fact exist, though they are rather inaccurate. However, for this to be practical, scientific understanding of how gut permeability relates to health needs to be much deeper. Doctors diagnose hypertension because there is a large body of scientific evidence describing how blood pressure relates to the risk of cardiovascular disease. Moreover, there is high quality evidence that when hypertension is treated, the risk of cardiovascular disease is greatly reduced. The same cannot yet be said for ‘leaky gut’.

Should Healthy People Worry About Gut Permeability?

So, a leaky gut does not get the status of syndrome or disease, but can we at least confirm that higher gut permeability is undesirable? 

As already mentioned, high gut permeability is in theory a bad thing. It allows undigested food, pieces of bacteria and anything else that is best kept within the intestine to leak into the blood, causing inflammation both locally and elsewhere in the body. We’ve already discussed how increased gut permeability seems to be an important feature of inflammatory bowel disease, but evidence for other conditions is sometimes tenuous. For example, it is sometimes claimed that ‘leaky gut’ can cause obesity or diabetes and explains why some people cannot seem to lose weight, but recent reviews state that even the evidence that gut permeability is increased in obesity is fairly weak. Where a correlation exists, it’s not clear that a ‘leaky gut’ contributes to obesity rather than the other way around, or equally likely, that genetic factors or an unhealthy lifestyle leads to both obesity and a ‘leaky gut’. It is certainly not justifiable to claim that a ‘leaky gut’ can, by itself, make you obese or diabetic. The link between gut permeability and conditions like arthritis and chronic fatigue is also mostly speculative.

For these reasons, any attempts by individuals to measure gut permeability such as using commercial testing kits are unlikely to be worthwhile. Not only are these measurements unreliable as already mentioned, but there’s no telling what they actually mean from a health perspective. To illustrate why this is a bad idea, imagine buying a test that says you have abnormally high levels of sugar in your urine, then concluding you have ‘leaky kidney’ and searching for remedies online…

The Take-Home Message

‘Leaky gut syndrome’ is an inaccurate and potentially harmful term, but gut permeability does vary from person to person and seems to correlate with some diseases. However, there is not nearly enough quality evidence to suggest that ‘leaky gut’ causes any disease. That said, high gut permeability is unlikely to be desirable for general health, given its potential to increase chronic inflammation. Furthermore, much of the health advice for preventing or reversing leaky gut is just good advice for gut health in general. With that in mind, it may not be a bad idea to explore some of this advice and whether it actually works. This will be the subject of part II.