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Why You're STILL Battling With IBS Symptoms (and what to do about it) - Click Here to Find Out NOW

IBS Diagnosis And Breath Testing

How is IBS (Irritable Bowel Syndrome) diagnosed?

To diagnose IBS or any condition for that matter, the physician uses the most appropriate, most effective, and most accurate test/procedure based on the most recent scientific evidence, and starts with the least invasive option possible. They don’t just pick any old test that they like doing! They use scientific evidence to guide their decisions and base it around you.

IBS is diagnosed by your physician or gastroenterologist who will speak with you about your symptom experiences and your bowel habits and see if these match the IBS diagnosis criteria, and by completing blood tests (NICE, 2017). They also look out for ‘red flags’ which could be a sign of cancer or inflammatory bowel disease (IBD) (– because you wouldn’t want these diagnoses to be missed and consequently delay important and potentially urgent treatment).

Currently there is no specific “IBS marker(s)” that physicians can test for to say, yes, this person has IBS. So, diagnosis is based on IBS specific criteria for symptoms and in the UK, clinical guidelines recommend blood tests to rule out other diagnoses, like Coeliac disease and IBD so that the condition can be appropriately managed and monitored, because although different conditions have similar symptoms, they can be caused by different things and require different treatment and management.

Clinical guidelines, which are based on the most recent and most robust scientific evidence available, for the diagnosis of IBS are generally very similar, but with slight differences between countries. For example, the Canadian, American and UK guidelines all use symptom criteria such as the presence of abdominal pain (Lacy et al., 2021; Moayyedi et al., 2019; NICE, 2017), but the guidelines slightly vary with what blood and pooh tests are recommended. 

🤔 Maybe you’ve been suffering with some gut symptoms such as wind, bloating and diarrhoea, and instead of going to your GP or family physician (perhaps because you think they’re too busy with other patients, or maybe you’ve previously felt like they don’t listen to you), so you’ve decided to get some breath tests done.

How do breath tests work?

The principle behind these tests is that once you’ve consumed the carbohydrate, any unabsorbed carbohydrate will travel into the large intestine and is then fermented by the gut bacteria that naturally live there, which then produces gas (Yao & Tuck, 2017).

Some of this gas can be absorbed into the bloodstream and taken to the lungs, so when you breathe out it can be collected and assessed (Kim et al., 2020). 

This all sounds good until you dig into it!

Recently I came across a lady who said she’d been to see a holistic doctor who used a lactulose (not lactose) breath test to test for SIBO (small intestinal bacterial overgrowth), IBS and Coeliac disease.

This lady was told that she doesn’t have Coeliac disease but was diagnosed with SIBO and IBS.

👉 But unfortunately, lactulose breath tests are unable to give this information. And this is due to several reasons…

  • Lactulose breath tests are UNRELIABLE (Shah et al., 2020; Yao et al., 2017) regardless of which condition it’s trying to detect. But despite this, lactulose breath tests have been commonly used to (attempt to) diagnose SIBO because they are cheaper and non-invasive (i.e., no cutting or insertion of any instruments into your body) compared to the alternative, which is seen as the “best” method, which involves passing a long thin flexible tube (an endoscope) into your small intestine to take a small sample of fluid to see what bacteria grows (Rao & Bhagatwala, 2019).

Lactulose breath tests are flawed!

  • Lactulose breath tests have several flaws, for example:

  • It’s difficult to repeat and get the same results (Yao et al., 2017).
    • They have poor ability to correctly identify people with and without SIBO.
    • The test results can be influenced by various factors, such as the person interpretating the results; the method used to do the test; what you’ve previously eaten and how long ago; how quickly your stomach contents empty into your small intestine; the speed at which food travel through your gut; the use of any medications or supplements leading up to the test (Kim et al., 2020; Rezaie et al., 2017); and possibly your age and gender (Newberry et al., 2016).
    • Lactulose has the ability to increase ‘transit time’ – how quickly food passes through the digestive system. It can be used as a laxative because we don’t have the ability to digest and absorb it, so it travels into the large intestine, and draws water into the bowel (BNF, 2021). BUT… as a side note, before you dash out and buy some because you’re suffering with constipation, be sure to check with your physician or pharmacist first to see if it’s suitable for you as it’s not appropriate for everyone to use (BNF, 2021).
  • As with IBS, there are clinical guidelines for diagnosing Coeliac disease… which does not include breath testing! …but, in case you’re interested, it does include blood tests for specific antibodies and can involve a biopsy – a sample of the lining of the small intestine is taken to see if there is any damage. And if Coeliac disease is diagnosed, they may do additional tests to assess how the condition has affected you so far, as there are complications of this disease if left untreated such as certain nutritional deficiencies, osteoporosis, and small bowel cancer. 


  1. If you’re yet to have a diagnosis for your gut symptoms, see your medical doctor/GP/physician who will use evidence-based clinical guidelines to inform their decisions.
  2. Don’t try to self-diagnose – medical doctors train for many years and have years and years of experience, so how can you possibly know and understand more than them!! Leave the diagnosis to the professionals!
  3. I don’t recommend using an alternative medicine practitioner to give you a diagnosis either, because they offer numerous alternative tests, investigations and diagnoses and some of which are based on uncertain scientific principles, which then risks delaying getting the correct diagnosis and treatment.
  4. Don’t waste your money on breath tests, especially not lactulose tests, and don’t bother with home testing kits which rely on you knowing what you’re doing!
  5. Go to a clinical nutrition professional – a Dietitian, who bases their recommendations on scientific evidence and will help you with your gut symptoms. They can help you identify the cause(s) and work with you to come up with a bespoke plan that suits YOUR personal needs. 

Best wishes to you!


N.B. It is crucial to get your food and fluid intake right if you want to control your IBS symptoms and if you want train harder, go faster and recover quicker from training sessions and competitions. Dietary requirements are highly individualised and there’s no ‘one size fits all’ approach. Working with a Registered Clinical & Sports Dietitian to develop a bespoke plan based on your unique requirements will help to ensure the most appropriate strategy and best results are achieved for your symptoms and exercise performance. 

The information, including but not limited to, text, graphics, images and other material contained on this website are for informational purposes only. No material on this site is intended to be a substitute for professional medical advice, examination, diagnosis, or treatment. Always seek the advice of your physician or other qualified health care provider with any questions you may have regarding a medical condition or treatment and before undertaking a new treatment or health care regimen, or before making any changes to your existing treatment, and never disregard professional medical advice or delay in seeking it because of something you have read on this website.

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