Small Intestinal Bacterial Overgrowth (SIBO) is now recognised as a major cause of irritable bowel syndrome (IBS). But SIBO is not the same as IBS: it’s a distinct disorder caused by too many bacteria living in your upper digestive tract. In fact, studies have shown that the incidence of SIBO in IBS sufferers could be as high as 84%. But because SIBO symptoms are also the symptoms of many other gut disorders, you need to find out what you’re dealing with before you treat it. Taking a SIBO test can be a great way to start digging deeper into your gut health. That’s why it’s a key test in our Microbiome Testing Kit Range.

SIBO is caused by an overgrowth of the commensal (friendly or neutral) bacteria, that live in your small intestine. Normally, your small intestine is free from excess bacteria but changes within it can make them overgrow, giving you uncomfortable symptoms: SIBO.

Breath tests for SIBO analyse samples of your breath to measure the gases that the bacteria in your small intestine are producing. Based on the levels of gases, experts can see if bacterial overgrowth is likely to be causing your symptoms.

Read on to learn more about SIBO testing, and why it could be important for you.

At IBS Clinics we recommend the SIBO breath test with lactulose. You can now buy this test directly from us, take it at home and get your results in 7-10 days.

Common SIBO symptoms

  • Bad bloating
  • Excessive gas
  • Diarrhoea 
  • Nausea
  • Abdominal pain
  • Fatigue
  • Food intolerances
  • Unwanted weight loss
  • Vitamin and mineral deficiencies that can lead to malnutrition

It’s also really important to look out for constipation.

A Quick Overview of SIBO

First let’s recap on what SIBO is:

Small Intestinal Bacterial Overgrowth (SIBO) happens when there’s an increase in the number of bacteria in your upper gastrointestinal tract, or small intestine. Today, some researchers think that the types of bacteria there could cause problems too.

In your small intestine,  bacteria ferment the carbohydrates you eat and release gas as a by-product. They also eat some of the nutrients in your food, leaving you with less. The gas and/or the stealing of nutrients leads the symptoms in the panel on the left.

The symptoms of SIBO are non-specific, meaning they’re similar to other digestive disorders like irritable bowel syndrome (IBS) or lactose intolerance. Many people with SIBO symptoms have been misdiagnosed with irritable bowel syndrome.

There are two main types of SIBO. If you have constipation, you’re more likely to have a particular type of SIBO. In the ‘main’ type of SIBO, bacterial fermentation in your small intestine releases hydrogen gas, so if you have that kind of SIBO, you’ll have elevated levels of hydrogen in your GI tract.

But SIBO can also cause an increase in methane levels. Hydrogen feeds single-cell organisms in your gut called archaea, which produce methane. Because methane uses up all the hydrogen, you’ll get a false negative result if your test only measures hydrogen. The NHS may only test for hydrogen, depending on where you live. SIBO tests that measure both gases sometimes record high methane and no hydrogen gas.

Best UK SIBO Test

Every SIBO breath test uses a carbohydrate solution that you’ll drink before giving your breath samples. There are lactulose breath tests, glucose breath tests and fructose breath tests. They all have their own benefits and drawbacks. Which one is the best?

Lactulose can give false positive results, whereas a SIBO breath test using glucose is unlikely to give you false positive results. But using lactulose can reveal SIBO in any area of your small intestine, unlike glucose, which is only likely to reveal it in the first section. However, no SIBO test is perfect. the main limitation of any type of SIBO breath test is that it can’t always distinguish between gases from your small intestine and gases from your large intestine. 

Talk to us before choosing your SIBO test. SIBO breath tests are difficult to interpret on your own, but a useful tool with the help of a skilled practitioner like one of the team at IBS Clinics. We look at your symptoms and your health history together with your test data to create a plan to reclaim your gut health.

How to do a SIBO Test?

To do the at-home SIBO test, you’ll need to follow a restrictive diet on the day before the test and then fast overnight. The restrictive diet starts at lunch time on the day before you take the test. The test kit contains detailed guidance on the diet, but broadly the following foods are ok:

  • Chicken or turkey
  • Fish
  • Eggs (poached or boiled only)
  • Hard cheeses
  • Clear chicken or meat broth
  • White rice or white bread

Overnight fasting starts after dinner on the day before the test.

SIBO Tests Online

Our SIBO test is an at-home breath test.

The SIBO breath test measures the hydrogen and methane present in your breath over a three-hour period. While some clinics give you the option  to do the test on-site, not many people want to sit in a waiting room for three hours. 

Doing the test at home is easy, safe, and doesn’t affect the validity or accuracy of the results at all.

Because bacteria ferment carbohydrates and release hydrogen and methane as a by-product, if the gases are present in your breath over a certain level, we know that you have SIBO.

At the beginning of the test (and after you’ve given a baseline sample), you’ll drink a carbohydrate solution. As your bacteria get to work on fermenting it, 80% of the gases produced go through your intestines, but the other 20% is absorbed into your blood and ends up in your lungs—where you breathe it out. 

Preparing for the SIBO test at home

Taking a SIBO test at home is easy. The test kit comes with full instructions that guide you through how to prepare.

Because we want to get the most accurate result, there are some things you need to avoid in the month before you take it. That’s because things like antibiotics and certain supplements affect the levels of bacteria in your small intestine, and skew your result. 

4 weeks before the test

Finish taking any antibiotics. Talk to your GP if you are on long-term antibiotics.

1 week before the test

Stop taking any laxatives, if you can. Talk to your GP to confirm this is safe first. 

1 day before the test

Avoid all complex carbohydrates and fermentable foods. These can interfere with the test results. You can read more about how and why to steer clear of these foods on the information in the test kit.

12 hours before the test

Fast and drink only water. Most people find it easy to do a SIBO breath test first thing in the morning, so they can fast overnight.

On the day of the test

Don’t smoke or exercise before or during the three-hour test period.

Make sure you follow the information on how to prepare for and take the test, to make sure your results are as accurate as possible.

You’ll begin by giving a baseline breath sample using the kit provided. Then you need to drink the sugary solution, and wait 30 minutes. After that, you’ll give your first real breath sample in a second tube. 

Then repeat the process with the rest of the tubes for a total of 2.5 hours. You’ll end up with seven breath-filled tubes to send off to the laboratory.

When it’s finished, you can resume your normal diet and any supplement regime. You should get your results back within 14 working days.

SIBO Test Kits - What's Included

Both lactulose breath and glucose breath tests are common, but which is the best? Taking a SIBO test can feel a bit overwhelming, but don’t worry, the instructions in the kit are easy to follow.

When the kit arrives, we recommend that you sit down and lay all the pieces out on a table to get familiar with them. Then, when you’re ready to take the test, you’ll know exactly what you’re looking at.

The test kit includes:

  • 1 x test instructions
  • 1 x dietary advice sheet
  • 1 x patient request form
  • 1 x mouthpiece and bag
  • 1 x mouthpiece instruction kit
  • Glass tubes
  • Sample tube labels
  • 1 x bubble wrap returns packet
  • 1 x postal bag

At IBS Clinics, we offer three types of SIBO tests from two different laboratories:

Invivo offers fructose and glucose breath tests.

Genova Diagnostics offers lactulose.

If you use the Genova test, you’ll need to provide your own lactulose. You can buy this easily from a chemist or pharmacy.

If you’re uncertain what test to choose, read our guidance below or contact us.

If you choose the Genova test, the laboratory will send the solution you choose along with the kit.


SIBO Test in London

Our SIBO test is an at-home breath test. 

While you can go to some private clinics to have a nurse take your breath samples, we don’t think it’s necessary to travel or pay the extra cost that comes with attending in-person.

We strongly recommend that you follow up your test with a consultation with us. Navigating through the huge amount of conflicting information on the internet about how to treat SIBO is confusing, overwhelming and doesn’t usually yield great results.

We see most of our clients over Zoom, so although you can come to our clinic for a face-to-face appointment, talking to us from home is a great way to get your results, an explanation and your personalised treatment plan.

Even experts still don’t always agree on what constitutes SIBO or how to treat it.

Because SIBO is a fairly new disease in terms of research and practice, there’s a lack of standardisation for test results. A group of experts met in 2017 to agree on some guidelines, which were summarised in ‘The North American Consensus’.

If you want to diagnose yourself, the general consensus is that a rise in hydrogen of 20 p.p.m. (parts per million) from baseline within 90 minutes means you’re positive for hydrogen-predominant SIBO.

For methane, a level of at least 10 p.p.m at any time is considered positive for intestinal methanogen overgrowth.

There’s also a third kind of SIBO, where hydrogen sulphide dominates over hydrogen and methane. While there’s currently no way to test for hydrogen sulphide SIBO specifically in the UK, we use a process of elimination. If both hydrogen and methane are very low throughout the three hours (we call this a ‘flatline’) hydrogen sulphide SIBO is likely.


SIBO Test Cost

Ten years ago, most medical doctors thought SIBO was a rare condition, and not many NHS trusts carried out the test.

The wealth of research now available on SIBO means testing and treatment is increasingly available on the NHS. As a result, your GP may refer you to a gastroenterologist who can carry out the test. Your local NHS trust may not yet offer SIBO testing. Many gastroenterologists only test for hydrogen SIBO, meaning that if you have excess methane, or hydrogen sulphide, you’ll get a false negative result.

Combined with the waiting time to see a gastroenterologist—which is usually well over six weeks—that means you might want to pay for a SIBO test privately.

Most SIBO breath tests cost between £139–£200. The test we use at IBS Clinics costs between £139 to £165, depending on which carbohydrate solution you want to use.

You can choose between glucose, fructose and lactulose. They each have their merits and disadvantages, but we usually recommend lactulose.

Glucose is absorbed in the upper part of the small intestine, which means it doesn’t often reach the colon (large intestine). This can mean that bacterial overgrowth present in the last portion of the small intestine will not be recorded on the test, giving a false negative result. 

But because glucose is quickly absorbed in the upper part of the small intestine it may not reach the lower part of the small intestine, which is a common site for SIBO, giving you a false negative result.

Lactulose is non-absorbable, so we know that it will travel all the way through your small intestine, making a false positive result possible, especially if you have diarrhoea or a fast transit time. While lactulose sounds like lactose, it’s not the same, so it’s usually fine for people who are lactose-intolerant to take. However, if you have a lactose allergy, ask for one of the alternatives.

There’s a lot of research both for and against the use of both types of solutions for SIBO testing. Most UK labs we work with recommend lactulose testing in the first instance.

You can also carry out your SIBO test using fructose as the carbohydrate solution. Many types of bacteria consume fructose, so if you tested negative using lactulose and/or glucose, it might be worthwhile using fructose.

The cost of our SIBO test includes all test materials, results and a brief, easy-to-understand report that shows the levels of your gases over the three-hour test.


SIBO Treatment

Your test results will tell you if you have excess hydrogen or methane gases in your small intestine. You could also have excess hydrogen sulphide. 

If your breath test is negative for both hydrogen and methane gases, and your results show a ‘flat line’ throughout the whole test, it’s possible you have a third type of overgrowth, which produces hydrogen sulphide. Hydrogen sulphide doesn’t show on the test, but a practitioner can deduce that it may be present by looking at your results.

It’s important to get rid of these misplaced bacteria, but it’s also crucial to improve the ‘terrain’ of your gut too, by following an appropriate diet and using the right supplements.


We almost always recommend a low fermentable-carbohydrate diet, because fermentable carbohydrates—found mostly in pulses, fruits and vegetables—feed bacteria. You’ll need to cut down on certain types of these foods for six to eight weeks to essentially starve your excess bacteria.

The low-FODMAP diet and the Bi-Phasic Diet are examples of this type of diet.


It’s likely that your treatment plan will contain some kind of antimicrobial. We can’t prescribe antibiotics, but we can recommend herbal alternatives which have been found in numerous studies to be just as effective.

There are specific antimicrobials for each type of overgrowth. Oil of oregano, berberine, neem and garlic are all common. We usually give SIBO clients eight to 10 weeks on one or more antimicrobials, alongside a low-fermentable diet.

Probiotics and prebiotics

Probiotics and prebiotics in SIBO treatment are controversial. We know from research that the success of probiotics appears to be down to the specific strain used, so it’s vital to choose the right probiotic supplement. We also know that certain types of bacteria can exacerbate SIBO.

For example, the species Lactobacillus casei, Bifidobacterium breve and Bifidobacterium bifidum, seem to support SIBO. A type of yeast called Saccharomyces boulardii is also useful.

Preventing recurrence

SIBO has a high relapse rate if the root cause isn’t addressed.

Common root causes include:

  • Low hydrochloric acid in your stomach
  • Slow gut motility (food isn’t moving through your gut at the proper rate)
  • Low pancreatic juices and bile
  • A faulty ileocaecal valve (the ‘door’ between your small intestine and large intestine)
  • Low secretory immunoglobulins (substances that protect your gut from outside invaders)

If you have SIBO, one or more of these things caused it. To stop it coming back, you need to address those causes. Our nutritionists all have extensive experience in addressing the causes and tackling the symptoms of SIBO.


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