Do you often feel bloated? Tired? Gassy? Suffer from brain fog? A quick Google search of your symptoms will soon point to a scary-sounding diagnosis – leaky gut syndrome. The term has taken off across social media and wellness circles, with claims it explains a wide range of health issues.
I do understand why people might be tempted to be tested for ‘leaky gut’, or buy supplements that ‘treat’ it, because it seems to offer a simple explanation for vague symptoms where medicine can struggle to find a clear answer.
And leaky gut is a recognised thing: the problem is the social media version of it is very different from the actual science – and the ‘solutions’, such as avoiding dairy or gluten, are meaningless.
When scientists talk about leaky gut (doctors won’t use the term as it’s not a medical diagnosis, but more on that later), they’re talking about the gut barrier becoming more permeable, so more compounds cross through into the body than normal.
This reflects how tightly the cells lining your gut hold together.
Your gut lining is just one cell thick, forming a selective barrier that allows nutrients to pass through, while keeping harmful microbes and toxins out.
When that barrier becomes ‘leakier’, that means the tiny gates between gut cells aren’t closing as tightly.
When scientists talk about leaky gut, they’re talking about the gut barrier becoming more permeable, so more compounds cross through into the body than normal
This can often happen temporarily through everyday activities – then the gaps tighten up again. Intense exercise can do this – after an hour of cycling, for example, the gut is more permeable for nearly an hour before bouncing back, researchers reported in the journal PLoS One in 2011.
Animal studies suggest the same can happen when you’re stressed – chronically or temporarily – and when you drink alcohol: the equivalent of just two vodka cocktails caused fragments of bacteria to leak from the gut into the bloodstream, with some effects lasting up to 24 hours, according to a 2014 study in PLoS One.
But more commonly it’s related to gut conditions such as coeliac disease (if the person affected isn’t on a gluten-free diet) or during flare-ups of inflammatory bowel disease – in both cases the gut lining is actively inflamed or damaged – or with irritable bowel syndrome (IBS). However, not everyone with a gut condition will have increased gut permeability.
The numbers affected with IBS, for example, vary depending on the study – it can range from 37 to 62 per cent of those with IBS with diarrhoea, reported the journal Therapeutic Advances in Gastroenterology in 2021.
Similarly, in people who had post-infectious IBS – a type of IBS where symptoms begin after catching a nasty tummy bug – between 17 to 50 per cent had a more permeable gut lining. The researchers suggested that diarrhoea-predominant IBS, as it’s known, and post-infectious IBS, often involve mild inflammation and over-activation of the immune system – which may make the tiny ‘gates’ between gut cells open up a little.
But (and this is key) while ‘leaky gut syndrome’ is often described online as a condition on its own that causes symptoms, doctors and scientists see it differently – not as a disease in itself, but as a symptom of something else.
And the early evidence suggests that having a more permeable gut lining only seems to matter when it’s combined with another problem.
In studies of mice where researchers deliberately made the gut barrier leakier, the animals remained healthy unless there was another factor, such as infection or inflammation – this let more bacteria and toxins cross the gut wall, fuelling further inflammation.
So while a leaky gut may make an illness worse, it doesn’t seem to be enough to cause one on its own, reported the journal Nature Reviews Immunology in 2009.
So forget pricey supplements for ‘leaky gut’, focus instead on eating a variety of fibre-rich foods – beans, wholegrains, fruit, vegetables, nuts and seeds – every day
Instead, if you’re struggling with ongoing gut symptoms, doctors will usually look for underlying causes such as coeliac disease, inflammatory bowel disease or food intolerances.
Then there’s the question of how gut permeability is measured.
In research trials, scientists measure it by giving people a drink containing two types of sugar molecules (one small, one large) and then measuring how much of each appears in the urine. If more of the larger molecule passes through, it suggests the gut lining is letting more substances through than usual.
But even in the research lab, there’s no reliable way to diagnose a leaky gut or to measure how many people actually have it – and that’s because the gut lining renews itself every few days, and we can’t directly see these microscopic changes without using invasive methods, such as collecting tissue samples of the gut.
You might have seen blood tests sold online claiming to measure zonulin, a protein that helps regulate how tightly the cells of your gut lining are held together. The idea is that higher levels of zonulin mean the gut barrier is ‘leakier’.
However, that’s an oversimplification, as zonulin is just one of many proteins involved in the gut barrier, and it’s also produced elsewhere in the body.
A 2017 study published in World Journal of Gastroenterology found that levels of zonulin in the blood fluctuate widely, changing from hour to hour and day to day.
None of the above means we shouldn’t care about a healthy gut lining. Far from it – and what that involves is focusing particularly on fibre.
Fruit and veg skin is also an important help – kiwi skin provides another 1g of fibre, as does the skin of a medium-sized potato
Fibre feeds your gut microbes: without enough fibre the hungry microbes turn to the gut lining itself for nourishment, according to research in mice – the microbes eat some of the protective mucus layer, reported researchers in a study published in Cell in 2016.
This allowed potentially harmful microbes to get closer to the gut wall, in turn disrupting the gut barrier.
When fibre was reintroduced, the mucus layer was restored, suggesting this damage may be reversible – at least in mice.
Fibre is key for gut health, yet the average UK adult eats just 16.4g a day (the recommended amount is 30g).
So forget pricey supplements for ‘leaky gut’, focus instead on eating a variety of fibre-rich foods – beans, wholegrains, fruit, vegetables, nuts and seeds – every day.
And don’t forget fruit and veg skin – kiwi skin provides another 1g of fibre, as does the skin of a medium-sized potato.