How useful are breath tests in diagnosing IBS?

Irritable bowel syndrome (IBS) is a common condition characterised by symptoms including abdominal bloating and pain, gas and diarrhoea. Poor absorption of carbohydrates known as ‘FODMAPs’ (Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols) is a leading cause of IBS symptoms in sensitive people.

The low FODMAP diet is used to determine which FODMAPs are triggers for different people. If you have gut issues, you may have also heard of breath testing. Hydrogen and methane breath tests are touted as painless and non-invasive ways to identify triggers of IBS symptoms. Tests include those for fructose, lactose, sorbitol and mannitol malabsorption.

But how do breath tests work, and are they worth doing?

How does breath testing for IBS work?

When you do not absorb a ‘FODMAP’ in the gut, it ferments in the large intestine and produces gas (hydrogen and/or methane).

You breathe this out, allowing it to be measured. Thus, the breath test involves breathing into a breathalyser device, after which you drink a sugar solution (varies depending on the test substance).

Further breath samples are taken at 15-30 min intervals over the next few hours. Symptoms such as bloating and gas should also be recorded.

How reliable is an IBS breath test?

Many factors may affect the result of a breath test.

These include gut transit time, smoking, exercise, diet and variations in the gut microbiota. Thus, a positive result does not mean you will get a positive result again, and vice versa. 

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Consequently, the repetition of the test is important if one is to make a diagnosis based on a breath test. Additionally, the dose provided during a breath test is much larger than you would habitually consume.

So, the test is really looking at your ability to handle a large dose of sugar, which can be misleading. Also, some FODMAPs (fructans and GOS) are fermentable in everybody, so we cannot breath test for intolerance to these.

Would we recommend a breath test?

In short – probably not. If limitations are considered, breath testing can be reasonably accurate and give some insight into what FODMAPs are poorly digested in IBS. However, these tests can be costly. Even if you do get a breath test, you’ll probably have to do the low-FODMAPs diet anyway. Especially if you really want to pinpoint your triggers and tolerance level.

Need help with the low FODMAP diet? Our FREE dietitian developed program will guide you through it, step-by-step. Includes a low FODMAP food guide. Sign up now.

If you are experiencing gut symptoms and have not been recommended a low FODMAP diet by a health professional, get started with the manage your gut symptoms program.

Reviewed by the healthylife Advisory Board March 2022