Professor Mohid Khan is a currently practising NHS Consultant Gastroenterologist and JAG-accredited endoscopist.
Written by Professor Mohid Khan
Consultant Gastroenterologist & Endoscopist
Honorary Professor, Cardiff University
Last reviewed: October 2026
Bloating is one of the commonest digestive symptoms I see in clinic. For some people it is an occasional nuisance. For others, the abdomen becomes progressively more uncomfortable or visibly distended during the day, clothes feel tighter, eating becomes difficult and there is a constant feeling that something is not quite right.
It is also a symptom that can send people down a confusing path of elimination diets, probiotics, supplements, breath tests, microbiome tests and sometimes repeated courses of antibiotics.
The difficulty is that bloating is a symptom, not a diagnosis. There are several possible causes, and more than one can be present at the same time. The useful question is therefore not simply:
'What test can I do for bloating?'
but:
'What is most likely to be causing my symptoms, and will another test actually change what we do?'
What do people actually mean by 'bloating'?
What do people actually mean by 'bloating'?
People use the word bloating to describe slightly different things.
Some describe an internal feeling of pressure, fullness or trapped wind.
Others notice genuine abdominal distension - their abdomen becomes visibly larger, often after meals or towards the end of the day.
Bloating may occur alongside:
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wind or excessive belching
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abdominal discomfort or cramps
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constipation
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diarrhoea or unpredictable stools
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feeling incompletely emptied after opening the bowels
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feeling full quickly after eating
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reflux or indigestion
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symptoms that improve after passing stool or wind
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Understanding that pattern often tells me considerably more than the word 'bloating' by itself.
What are the common causes of persistent bloating?
There isn't one single cause.
Common explanations include constipation, IBS, dietary fermentation and food intolerances. Some people experience increased sensitivity to normal stretching or gas within the bowel.
Other conditions such as coeliac disease sometimes need to be considered.
Upper gastrointestinal disorders can produce fullness or bloating that feels quite different from lower abdominal distension.
Medicines can contribute.
Previous surgery, bowel motility and other medical conditions may occasionally be relevant.
And sometimes more than one factor is operating at the same time.
That is why I prefer to start with the pattern of symptoms rather than assuming that persistent bloating automatically means IBS, SIBO or a 'microbiome imbalance'.
Could constipation cause bloating even if I open my bowels every day?
Yes.
This is surprisingly common.
Constipation does not necessarily mean going several days without passing stool.
Some people open their bowels daily but do not empty effectively. Others alternate between difficult bowel movements and looser stools.
Features suggesting constipation can include:
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hard or pellet-like stools
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straining
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feeling incompletely emptied
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repeatedly returning to the toilet
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long periods sitting on the toilet
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needing considerable effort to pass stool
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feeling better after eventually opening the bowels
If stool and gas are moving slowly through the bowel, bloating and abdominal distension can become much more noticeable.
Sometimes improving bowel function makes a much greater difference than performing increasingly complicated tests.
Could it be IBS?
Yes.
Bloating is extremely common in irritable bowel syndrome.
But IBS is not simply another word for “bloating and all my tests are normal”.
The diagnosis is based on a characteristic pattern of abdominal symptoms and altered bowel function, together with appropriate clinical assessment.
People with IBS can also become more sensitive to normal amounts of gas, movement and stretching within the bowel. The symptoms can therefore be very real even when scans or endoscopy are reassuring.
A diagnosis of IBS can be entirely appropriate when the clinical pattern fits.
It should not, however, be used as a convenient label to stop thinking w. history does not fit or when there are features that need further investigation
What about food?
Food can certainly influence bloating.
Certain carbohydrates are poorly absorbed or readily fermented by bacteria within the intestine. This can increase gas and fluid within the bowel and provoke symptoms in susceptible people.
Lactose is one example.
Other fermentable carbohydrates are often grouped together under the term FODMAPs.
But I would be cautious about progressively removing more and more foods.
I sometimes see people who have stopped gluten, dairy, onions, garlic, fruit, legumes and several other foods without being sure which, if any, actually caused their symptoms.
An increasingly restricted diet can make eating socially difficult and can sometimes compromise nutrition.
If dietary manipulation is needed, a targeted approach - sometimes with help from a specialist gastrointestinal dietitian - is usually preferable to progressively excluding foods yourself.
Should I stop gluten?
Not automatically.
Some people clearly notice more symptoms after bread, pasta or other wheat-containing foods.
That does not necessarily mean gluten itself is responsible. Wheat also contains fermentable carbohydrates that can provoke symptoms in some people with IBS.
More importantly, if coeliac disease is a possibility, testing is generally much easier to interpret while gluten is still being eaten.
Going strictly gluten-free before being assessed can therefore occasionally make the diagnostic process more difficult.
What is SIBO?
SIBO stands for small intestinal bacterial overgrowth.
It refers to an abnormal increase or pattern of bacteria within the small intestine.
Symptoms attributed to SIBO commonly include:
bloating
excess wind
abdominal discomfort
diarrhoea
altered bowel habit
The difficulty is that these symptoms overlap enormously with IBS and several other gastrointestinal disorders.
You cannot reliably diagnose SIBO simply from symptoms.
How useful are SIBO breath tests?
Hydrogen and methane breath tests are sometimes used when SIBO is clinically suspected.
During the test, a carbohydrate such as glucose or lactulose is taken and gases produced within the gastrointestinal tract are subsequently measured in the breath.
These tests can provide useful information in the right clinical situation.
They are not perfect.
The result can be affected by factors including which substrate is used, how quickly material travels through the intestine and how the timing and pattern of gas production are interpreted.
That means a positive test should not automatically be treated as proof that SIBO is responsible for every symptom.
I prefer to interpret a breath test in the context of the patient's symptoms, medical history and - importantly - why SIBO might have developed in that person in the first place.
If antibiotics helped me before, does that prove I have SIBO?
No.
It can be useful information, but it does not prove the diagnosis.
Antibiotics such as rifaximin can alter intestinal bacteria and some people report significant improvement after treatment.
But improvement is not completely specific for SIBO.
If symptoms repeatedly return after treatment, the more useful question may be:
'Why do these symptoms keep recurring?'
Depending on the situation, that may lead us to think about constipation, bowel motility, medication, diet, previous surgery or another gastrointestinal disorder rather than simply repeating courses of antibiotics indefinitely.
What about microbiome and commercial stool tests?
There is now a large market in commercial stool tests, microbiome profiles and tests describing 'dysbiosis'.
The science of the gut microbiome is genuinely interesting.
The difficult part is translating a very detailed list of bacteria found in a stool sample into an explanation for one person's symptoms and a treatment that is known to improve them.
There are also conventional stool tests with established medical uses - for example tests looking for bowel inflammation, infection or pancreatic digestive function.
These are answering very different questions from a broad commercial microbiome profile.
If you are considering a commercial gut test, or already have results and are unsure what they mean, I am happy to review them in the context of your symptoms.
Read: Gut microbiome and stool tests - which tests are actually useful?
Do I need blood tests or stool tests for bloating?
Sometimes, but the investigations depend on the clinical situation.
For somebody with longstanding symptoms that fit a typical IBS pattern and no concerning features, extensive investigation may not be needed.
In other circumstances it can be reasonable to look for conditions such as coeliac disease, anaemia, inflammation or other clues that suggest a different explanation.
Someone whose main problem is diarrhoea may need a different assessment from somebody who is predominantly constipated.
Upper abdominal fullness may require a different approach again.
There is therefore no sensible universal 'bloating panel' that investigates everyone.
Do I need a gastroscopy or colonoscopy?
Usually not simply because bloating is present.
Gastroscopy and colonoscopy are valuable tests when there is a clinical reason for performing them, but neither is a universal investigation for bloating.
A gastroscopy may be appropriate where particular upper gastrointestinal symptoms or concerns are present.
A colonoscopy may be appropriate in selected patients with persistent change in bowel habit, rectal bleeding, iron-deficiency anaemia, inflammatory markers or other relevant features.
But a patient with otherwise typical IBS does not automatically need an endoscopy simply to confirm that diagnosis.
The investigation should fit the clinical question.
What if my tests have already been normal?
This is extremely common.
A normal blood test, scan, gastroscopy or colonoscopy can be very reassuring.
But reassuring is not the same as explanatory.
Different investigations answer different questions.
A normal colonoscopy, for example, tells us a great deal about important conditions affecting the colon but does not investigate every possible cause of abdominal bloating.
Sometimes the most useful next step is therefore not another test.
It is to look carefully at:
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what has already been investigated
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what those tests genuinely excluded
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whether anything important has been missed
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and whether the original diagnosis still makes sense
That can be considerably more useful than simply starting the investigation process again.
When might doing more tests actually make things less clear?
This is an important part of gastroenterology.
When symptoms continue without a clear explanation, it is understandable to keep searching for another test.
Sometimes that is exactly the right thing to do.
But every test also has the potential to identify incidental findings, borderline abnormalities or results whose significance is uncertain.
That can occasionally create a new cycle:
symptoms → test → uncertain result → another test → another uncertain result
without anybody stepping back to ask what problem we are actually trying to solve.
A specialist assessment should therefore consider two separate questions:
Is there something important that still needs to be excluded?
and:
Will another investigation genuinely change what we do next?
Sometimes good specialist care means investigating further.
Sometimes it means knowing when not to order another test.
When should bloating be investigated more carefully?
Most bloating is not caused by something serious.
However, I would be more cautious when symptoms are associated with features such as:
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unexplained weight loss
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iron-deficiency anaemia
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persistent or significant rectal bleeding
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a new and persistent change in bowel habit
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persistent vomiting
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progressive difficulty swallowing
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symptoms that wake you regularly at night
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abnormal blood or inflammatory markers
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a relevant family history of gastrointestinal cancer or other significant gastrointestinal disease
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symptoms that are steadily progressing rather than fluctuating
Bloating can also occasionally arise from conditions outside the gastrointestinal tract. In women, for example, new persistent abdominal distension or bloating may sometimes require consideration of a pelvic or gynaecological cause rather than assuming it is IBS.
Sudden severe abdominal pain, repeated vomiting, significant bleeding or being acutely unwell should of course be assessed urgently rather than waiting for a routine consultation.
There isn't a standard 'bloating package'.
I start by understanding the symptom properly. I want to know whether the abdomen actually distends, when symptoms occur, their relationship with eating, bowel habit, abdominal pain, medicines, diet and previous treatments.I also want to know what investigations have already been performed.
One of the most useful questions is often: 'What has genuinely been ruled out, and what has simply been assumed?'
From there, the next step might involve targeted blood or stool tests, treatment of constipation or IBS, dietary input, reviewing previous investigations, breath testing in selected circumstances, imaging or endoscopy where there is a good reason - or sometimes avoiding further investigations that are unlikely to help. The aim is not to produce the longest possible list of tests.It is to arrive at a sensible working explanation and a clear plan.
Considering a private gastroenterology opinion?
If you have persistent bloating, suspected IBS or SIBO, conflicting test results, or symptoms that remain unexplained despite previous investigations, I am happy to review the overall picture.
I see patients personally at Nuffield Health Cardiff Bay and can also offer online consultations where clinically appropriate.
Professor Mohid Khan
Consultant Gastroenterologist & Endoscopist
Honorary Professor, Cardiff University
Frequently asked questions
Is persistent bloating usually IBS?
IBS is a common cause of bloating, particularly when bloating occurs alongside abdominal discomfort and a change in bowel habit. However, bloating has many possible causes, so the overall symptom pattern and any warning features need to be considered rather than assuming every case is IBS.
Can constipation cause bloating even if I open my bowels every day?
Yes. Some people open their bowels daily but do not empty effectively. Straining, hard stools, incomplete emptying or repeatedly returning to the toilet can suggest constipation even when bowel movements occur every day.
How do I know whether I have SIBO?
Symptoms alone cannot reliably diagnose SIBO because bloating, wind, abdominal discomfort and diarrhoea overlap with IBS and other conditions. Breath testing may be useful in selected patients but needs to be interpreted in the clinical context.
Is a positive SIBO breath test definitely the cause of my symptoms?
No. Breath tests have limitations and a positive result needs to be interpreted alongside the symptoms, medical history and reason SIBO might be present.
Do I need a colonoscopy because I am bloated?
Usually not for bloating alone. Colonoscopy may be appropriate if there are other indications such as bleeding, iron-deficiency anaemia, persistent bowel-habit change or another clinical concern.
Should I have a microbiome test for bloating?
Commercial microbiome testing can provide detailed information about organisms detected in a stool sample, but it is not currently a routine diagnostic test for IBS or bloating. It is usually more useful to start with the symptoms and decide what specific clinical question, if any, needs testing.
Can you review tests I have already had?
Yes. Previous blood tests, scans, endoscopy reports, histology, breath tests or commercial gut-test results can be reviewed as part of the consultation. In many cases, understanding what has already been investigated is more useful than automatically repeating tests.