Key points
- Abdominal bloating is rarely due to excess gas: the problem usually lies in how the gut handles it and how it is perceived.1
- The commonest cause is a functional disorder (irritable bowel syndrome, constipation), but there are treatable causes worth ruling out, such as coeliac disease.1
- The SIBO breath test gives false positives: it makes sense when there are risk factors, not as a routine test.2,3
- IgG food tests do not diagnose intolerances.5
- A belly that swells as the day goes on is usually due to an uncoordinated diaphragm reflex that can be corrected with biofeedback.4
This article summarises the evidence and clinical guidelines so you can understand your situation. It does not replace an individual assessment.
Abdominal bloating, the swollen stomach that appears after eating or grows as the day goes on, is one of the commonest reasons to see a gastroenterologist. And one of the most frustrating: many people arrive after years of increasingly strict diets, intolerance tests, microbiome analyses and SIBO treatments, without getting better.
The good news is that there is almost always an identifiable explanation and a sensible treatment. And it almost always involves fewer tests, not more, but the right ones.
Bloating and distension are not the same
Although the words are used interchangeably, they are two different things, and telling them apart helps a great deal with diagnosis:1
- Bloating is the sensation of pressure, fullness or trapped wind.
- Distension is a real, visible increase in the size of the abdomen: the belly that grows and makes you loosen your belt.
Many patients have both, but not always. Some people feel intense bloating with no visible change, and others have marked distension that barely bothers them.
Why it is rarely “too much gas”
It is the explanation most often given and one of the least accurate. When it is measured, the amount of gas in the abdomen of people with distension is usually normal or almost normal.1
What goes wrong is something else:
- How gas is distributed and moved along. A gut that moves it with difficulty holds it in certain segments.
- How intensely it is perceived. In irritable bowel syndrome, normal amounts of gas are felt as uncomfortable (visceral hypersensitivity).
- How the muscles respond. In visible distension, the diaphragm descends and the abdominal wall relaxes instead of contracting, pushing the contents forward.4
That is why treatments aimed only at “getting rid of gas” work so poorly.
The causes that do need ruling out
Before putting a label on anything, a few specific causes should be checked, because several have a specific treatment:1
| Cause | What suggests it | How it is investigated |
|---|---|---|
| Irritable bowel syndrome | Pain related to bowel movements and changes in bowel habit | Clinical history and basic blood tests; no complex tests needed |
| Constipation | Hard stools, straining, a feeling of incomplete emptying (often not recognised as constipation) | Clinical history; sometimes anorectal manometry |
| Coeliac disease | Diarrhoea, iron-deficiency anaemia, relatives with coeliac disease | Blood antibodies while eating gluten and, if positive, gastroscopy with biopsies |
| Lactose or fructose malabsorption | A clear link with dairy or fruit | Withdrawal and reintroduction, or a specific breath test |
| Bacterial overgrowth (SIBO) | Previous abdominal surgery, motility disorders, diarrhoea with weight loss | Breath test in selected cases |
| Abdominophrenic dyssynergia | A belly that grows during the day and goes down overnight | Clinical history; in specialist centres, muscle activity studies |
| Delayed gastric emptying | Early fullness, nausea, feeling full after small amounts | Gastroscopy and, if appropriate, an emptying study |
Abdominophrenic dyssynergia deserves a mention: it explains many striking cases of distension, it is treatable and it is virtually unknown outside specialist circles. In a randomised trial from the Vall d’Hebron Hospital group in Barcelona, a few sessions of electromyography-guided biofeedback clearly reduced distension compared with a sham treatment.4
SIBO: it exists, but not as it has been sold
Small intestinal bacterial overgrowth is real and treatable. The problem is how it has become a label for almost any bloating.
It is usually diagnosed with a breath test: you drink a glucose or lactulose solution and the hydrogen and methane you exhale are measured over two to three hours. According to the North American consensus, a rise in hydrogen of 20 ppm or more within 90 minutes is considered positive, and methane of 10 ppm or more indicates an excess of methane-producing organisms, associated with constipation.3
The test has a considerable rate of false positives, especially with lactulose and in people with fast intestinal transit.2,3 Used as a screening test in everyone with a bloated belly, it produces many diagnoses that are not real, and with them unnecessary courses of antibiotics.
| Testing makes sense | Testing does not make sense |
|---|---|
| Previous stomach or bowel surgery | As the first test for any bloating |
| Conditions that disrupt motility (scleroderma, long-standing diabetes) | Repeating it every few months |
| Diarrhoea with weight loss or vitamin B12 deficiency | Chaining treatments without revisiting the underlying diagnosis |
| Irritable bowel syndrome not responding to usual measures | Before coeliac disease or constipation have been ruled out |
When overgrowth is genuinely confirmed, the treatment of choice is an antibiotic that acts almost only in the gut, rifaximin.2
The tests that cannot guide decisions
It is worth being clear here, because this is where patients’ exhaustion is most exploited:
- IgG food tests. The European Academy of Allergy explicitly advises against them: IgG shows you have been exposed to a food, not that it disagrees with you.5
- Intolerance tests using hair, saliva, bioresonance or kinesiology. No scientific basis.
- Commercial microbiome analyses. Interesting for research, but they cannot currently guide individual clinical decisions.
The rule I follow
I order a test when its result will change what we do, and not before. If a test does not change the treatment, all it adds is a bill and anxiety.
The problem with ever-narrowing diets
A pattern I see often: one food is cut out, things improve for a few days, the bloating returns, another food goes, and so on for months. A year later the person eats six things and feels the same.
Dietary approaches work, but in phases and with structured reintroduction. The low-FODMAP diet (fermentable sugars) has three phases: 4-6 weeks of restriction, reintroduction by groups to identify which ones cause symptoms, and a maintenance phase that is as broad as possible. It is best done with a dietitian.1
Following a restrictive diet indefinitely and on your own impoverishes your diet, disrupts the gut flora and adds a new problem to the existing one. If food has become a constant source of worry, it is worth saying so in clinic: it is more common than it seems and it changes the approach.
Treatments that work
| Treatment | For whom |
|---|---|
| Treating constipation (soluble fibre, osmotic laxatives) | When there is underlying constipation; this improves distension fastest |
| Phased low-FODMAP diet | Irritable bowel syndrome with meal-related bloating1 |
| Rifaximin | Confirmed bacterial overgrowth2 |
| Biofeedback and breathing retraining | Visible distension due to abdominophrenic dyssynergia4 |
| Low-dose neuromodulators | When visceral hypersensitivity predominates1 |
| Strict gluten-free diet | Confirmed coeliac disease |
Common myths
“My belly swells because I have a lot of gas.”
The amount of gas is usually normal. The problem lies in how it is handled and perceived, and in how the abdominal muscles respond.1,4
“An IgG test told me which foods I am intolerant to.”
IgG reflects exposure, not intolerance. Allergy societies advise against these tests.5
“Almost all bloating is SIBO.”
SIBO is one cause among several, and the breath test gives false positives. Testing only makes sense in selected cases.2,3
“The more foods I cut out, the better I will feel.”
Indefinite restrictive diets impoverish your eating and do not improve symptoms in the long run. They work in phases with reintroduction.1
“Probiotics will fix it.”
The evidence is limited and inconsistent. They may help some people, but they do not replace a diagnosis.
“Bloating is psychological.”
It has measurable mechanisms: visceral hypersensitivity, altered transit and a muscle reflex that can be corrected.4
Warning signs: do not wait
These symptoms need investigating before any label
Functional bloating does not cause the following. If they appear, another cause must be looked for:1
- Unintentional weight loss
- Blood in the stools or black stools
- Anaemia or iron deficiency
- Persistent vomiting
- Fever
- Symptoms starting after the age of 50
- Distension that does not go down overnight or keeps increasing
- A family history of bowel or ovarian cancer, or of coeliac disease
- In women, persistent bloating of recent onset: a gynaecological cause should be ruled out
How I approach it in clinic
I start with a detailed history: when the bloating appears, how it changes during the day, your bowel habit, which diets and supplements you have tried and which tests you have already had. Often that alone makes the diagnosis fairly clear.
Then I only request the tests that will change something, starting with blood tests that include coeliac serology. And we design a step-by-step plan, starting with what usually works fastest, with follow-up to check that it is helping.
Have you had bloating for a long time and piled up tests without a clear diagnosis?
We review your case from the start and design a plan with the tests that genuinely change something.
Frequently asked questions
How do I know if I have SIBO?
How do I prepare for a breath test?
Usually no antibiotics in the previous four weeks, a diet low in fermentable foods the day before, fasting for 8 to 12 hours, and no smoking or exercise during the test.3
Why is my belly more bloated in the evening?
This is the typical pattern of functional distension. Gut contents build up over the day and the muscle reflex that pushes the abdomen forward is triggered. At night, at rest, it disappears.4
Is the low-FODMAP diet for life?
No. The strict phase lasts a few weeks, after which foods are reintroduced by groups. The aim is to eat as varied a diet as possible.1
Does SIBO come back after treatment?
It can recur if the underlying cause persists, such as a motility disorder or previous surgery. That is why identifying it matters.2
References
- Moshiree B, et al. AGA Clinical Practice Update on evaluation and management of belching, abdominal bloating, and distention: expert review. Gastroenterology. 2023. PubMed
- Pimentel M, et al. ACG Clinical Guideline: Small intestinal bacterial overgrowth. Am J Gastroenterol. 2020. PubMed
- Rezaie A, et al. Hydrogen and methane-based breath testing in gastrointestinal disorders: the North American consensus. Am J Gastroenterol. 2017. PubMed
- Barba E, et al. Correction of abdominal distention by biofeedback-guided control of abdominothoracic muscular activity in a randomized, placebo-controlled trial. Clin Gastroenterol Hepatol. 2017. Publication
- Stapel SO, et al. Testing for IgG4 against foods is not recommended as a diagnostic tool: EAACI Task Force Report. Allergy. 2008. PubMed
Links go to PubMed or the original publication and open in a new tab.
Related reading
Dr Fernando Casals Seoane
Consultant gastroenterologist with a PhD in Medicine from the Autonomous University of Madrid. He has worked at La Princesa University Hospital since 2009 and sees private patients at Ruber Juan Bravo Hospital. Certified by the European Board of Gastroenterology and Hepatology and honorary lecturer at the UAM. Principal investigator in international clinical trials on acute pancreatitis, including WATERFALL (NEJM, 2022).
Transparency: this article is not sponsored and does not promote any product or brand. All sources are linked.