Millions of people with a debilitating digestive problem are being fobbed off by GPs, putting them at risk of cancer, experts claim.

The condition, SIBO, which stands for small intestine bacterial overgrowth, is soaring in the UK, thought to be due in part to widespread overuse of heartburn tablets. The increasing number of patients taking weight-loss injections such as Mounjaro and Wegovy have also been blamed.

However, the symptoms, which include cramps, diarrhoea and flatulence, are often mistaken for irritable bowel syndrome (IBS), a lifelong condition which cannot be cured.

Some patients are even told by their GP that the symptoms are ‘in their head’ and are simply prescribed antidepressants, experts claim.

Left untreated, SIBO can cause vitamin deficiencies, kidney problems and has even been linked to cancer. However, studies show that, once diagnosed, it can be effectively cured using a course of antibiotics.

Experts are now calling on GPs to send patients with suspected SIBO symptoms for hospital tests and to ensure they get the correct treatment.

‘SIBO is often not taken seriously by NHS doctors,’ says Dr Marie Lewis, a gut disease expert at the University of Reading.

‘Once these patients have been tested for more serious diseases, such as cancer, and the result come back clear, doctors are mainly relieved that they don’t have anything life-threatening, so don’t investigate further.

Patients taking heartburn medicine, which reduces acid levels in the stomach, are more likely to develop SIBO. These common drugs are known as proton pump inhibitors (PPIs)

‘Patients with these unexplained symptoms should be tested for SIBO. Otherwise they might not receive the right treatment.’

So what is SIBO? To understand it, it’s helpful to know how the digestive system works.

The gut is made up of the small and large intestines. After food is digested in the stomach, it moves into the small intestine, where nutrients are absorbed.

What remains then passes into the large intestine, where water and salts are extracted. The large intestine is home to high levels of bacteria – most of them beneficial – which help produce essential vitamins and break down hard-to-digest nutrients like fibre. This thriving microbial community is known as the gut microbiome.

By contrast, the small intestine typically contains very few bacteria. But in people with SIBO bacteria begin to accumulate where they shouldn’t.

As food moves through the small intestine, these bacteria start fermenting it – producing gas as a by-product. That gas builds up and causes uncomfortable bloating, pain and diarrhoea. This is what’s known as SIBO.

Experts say there are a number of reasons why this might happen – most of which are linked to the body’s ability to digest food. Ordinarily, the majority of bacteria found in food are destroyed by acid in the stomach.

But when patients have low levels of stomach acid this can allow bacteria to begin to grow in the small intestine.

Studies show that patients taking heartburn medicine, which reduces acid levels in the stomach, are more likely to develop SIBO. These drugs, known as proton pump inhibitors (PPIs), which include omeprazole and lansoprazole, are some of the most commonly taken medicines in the UK.

One in five Britons have at some point taken a PPI, and prescriptions for omeprazole have tripled over the past two decades, which experts say could be driving an increase in cases.

However, SIBO is not only linked with a lack of stomach acid. It can also occur when the gut slows down, meaning it takes longer for food to be digested and transported to the large intestine.

This can create more opportunities for bacteria to escape into the small intestine.

Research shows that patients who have undergone surgery have slower guts, putting them at greater risk of SIBO. For this reason, women who have recently delivered a baby via caesarean section are more likely to develop the condition. Diabetes patients, who also often have impaired gut function, have an increased risk.

Experts believe that the rising number of patients taking weight-loss drugs will also lead to an increase in cases, as the weekly injections work by slowing down the digestive process.

It is estimated that more than 1.5 million Britons now pay for weight-loss jab prescriptions.

Experts say it is unclear how many SIBO patients are in the UK but some studies, including a 2022 UK study published in the medical journal Nature, argue that as many as half of patients with IBS – a bloating condition that affects 13 million Britons – may in fact have SIBO.

Ordinarily, patients with symptoms will first be checked for cancer as these can also be signs of life-threatening tumours. Patients will need to undergo a stool sample test and sometimes a gastroscopy, where a thin, flexible tube with a camera is threaded down the throat to the stomach.

Experts say that, if these tests are clear, then patients should be offered what is known as a breath test. This is a device designed to measure levels of the gases hydrogen and methane, produced by excess bacteria, in the patient’s breath.

Once identified, experts say the main SIBO treatment is an antibiotic called rifaximin, which research shows can eliminate the bacteria overgrowth in the small intestine.

The £2 tablet is taken three times a day for between two and eight weeks. Research shows that SIBO patients taking rifaximin are three times more likely to see a significant improvement in their symptoms compared to those not on the drug.

In some cases, patients say the treatment can slash the severity of their symptoms in a matter of weeks.

However, experts say the majority of NHS patients with suspected SIBO symptoms are not offered a breath test and, as a result, never receive rifaximin.

This is largely due to an ongoing debate about the accuracy of the test, which some research suggests can wrongly tell patients they have the condition. For this reason, some experts say they are hesitant to prescribe refaximin these patients.

‘Refaximin is effective at killing off bacteria in the small intestine, but it is not risk-free,’ says Prof David Saunders, a gut disease expert at the University of Sheffield.

‘It can also kill off healthy gut bacteria, which can lead to a whole host of other health problems. Overuse of antibiotics can also lead to the creation of drug-resistant bacteria.

‘So you want to be really sure that the patient has SIBO before you give them the drug.

‘The problem is that, due to the inaccuracy of the breath test, it’s hard to be sure about this, which is why so many doctors are resistant to offering the antibiotic.’

However, others disagree, arguing that the benefit of treating SIBO outweighs these risks. Studies show that, left untreated, the debilitating condition can trigger a number of serious health problems.

Patients with SIBO are often unable to absorb vital nutrients, leading to issues such as hair loss and anaemia – a severe lack of the crucial vitamin iron that causes severe fatigue. And, in 2016, a Chinese study involving more than 200 cancer patients found a significant link between SIBO and the development of pancreatic, bile duct and colon cancers.

‘The breath test may not be perfect but its the best tool we have currently to diagnose SIBO,’ says Prof Anthony Hobson, of The Functional Gut Clinic, which offers private SIBO testing.

‘Without it, patients can’t start rifaximin which means they will never get proper treatment. So refusing to test patients is as good as just giving up on them.

‘These are patients who are in intense pain. I often hear from people who say it is feels like they are being poisoned. Every year, we see thousands of patients who were unable to get help on the NHS, so they come to us.

‘The argument that treating them with antibiotics will cause more problems doesn’t make sense. There are always trade-offs in medicine. Would a respiratory specialist refuse to treat a chronic chest infection with antibiotics because this might trigger side effects? No, so why is it any different with SIBO?’

Regardless, all experts agree that there are other crucial steps SIBO patients can take to reducing their agonising symptoms.

Research shows that a low-fibre diet, often known as the FODMAP diet, is effective at tackling bacterial overgrowth in the small intestine. This is because much of this bacteria feeds off fibre – a nutrient found in certain fruits, vegetables, whole grains, pulses and nuts.

‘Once patients finish their course of rifaximin, we usually recommend they follow a FODMAP diet,’ says Prof Hobson. ‘This limits any gas build-up which takes the pressure of the small intestine, and can lower the risk of further SIBO flare-ups. Over time, they can eventually reintroduce these fibrous foods.’

Experts say it is also crucial to tackle any underlying causes of SIBO. ‘This might mean stopping taking acid reflux drugs such as omeprazole or coming off weight-loss jabs,’ says Prof Saunders.

‘There are also drugs patients can take to speed up the gut’s digestion process, such as metoclopramide, which we give to diabetes patients.’

But experts say it is crucial that GPs learn the signs of SIBO so patients can be diagnosed and access treatment.

‘GPs are not trained to spot SIBO,’ says Prof Hobson. ‘Once more dangerous issues, including cancer, have been ruled out, SIBO needs to be considered. Otherwise patients can go years without help.’

Antibiotics eased bloating misery 

Tiffini Shiel, 41, learned about SIBO earlier this year and ordered a £150 breath test with the private IBS & SIBO Clinics. This showed that she was suffering with the condition

For the past two years, Tiffini Shiel has lived in constant agony.

The 41-year-old charity worker from Surrey began to experience severe bloating in 2023 and was unable to pinpoint the cause.

‘It was there from the moment I woke up in the morning until I went to bed,’ says the mother-of-two, left. ‘I felt like my stomach was a balloon close to popping at all times.’

After seeking help from her GP, she was sent for hospital scans and also underwent a gastroscopy, where a camera is inserted into the mouth and threaded down to the stomach, but the tests did not show any issues. ‘My GP told me that I just had anxiety and that was probably causing the bloating,’ says Tiffini. ‘I was so upset because I knew that I wasn’t crazy – something was really wrong with me.’

Then, earlier this year, Tiffini learned about SIBO. ‘It matched what I was going through,’ she says. She ordered a £150 breath test with the private IBS & SIBO Clinics, run by functional medicine expert Emma Wells, that showed she was suffering with the condition.

Two months ago, Tiffini began taking the antibiotic rifaximin, along with another called neomycin, and gut health supplements. ‘The bloating has gone down to the point where I’ve lost almost a stone,’ she says. ‘My stomach no longer hurts. But SIBO patients shouldn’t have to go private. The NHS needs to take this condition more seriously.’