Bloating is one of the most common reasons people come to a gastroenterologist, and one of the most frequently dismissed. In a study of more than 51,000 people across 26 countries, around 18% reported bloating at least once a week over a three month period. Women reported it roughly twice as often as men.
It is common, it is usually benign, and it is occasionally the first sign of something that needs treating. This article is about telling those apart.
Bloating and distension are not the same thing
The distinction matters clinically, and most people use the words interchangeably.
- Bloating is the subjective sensation of fullness, pressure or trapped gas
- Distension is a measurable increase in the circumference of the abdomen
They often occur together but they can occur separately. Someone can feel intensely bloated with no visible change, and someone else can visibly distend through the day with little discomfort. The mechanisms behind them differ, and so does the treatment.
What normal bloating looks like
Some degree of bloating after meals is physiological. The gut produces gas as bacteria ferment carbohydrates that were not absorbed in the small intestine. Fibre, legumes, onions, certain fruits and artificial sweeteners all increase that fermentation.
Bloating is likely to be benign when it:
- Comes and goes, and relates to specific meals
- Is worse in the evening and better in the morning
- Improves after a bowel movement or passing wind
- Has been present intermittently for years without changing
- Occurs alongside a known condition such as IBS or functional dyspepsia
More than half of patients with irritable bowel syndrome, constipation or functional dyspepsia report bloating, and over 90% of those with constipation-predominant IBS do.
The most common underlying causes
Constipation. The most common and most treatable. Stool held in the colon increases fermentation and transit time. Around half of patients with chronic constipation also have a pelvic floor disorder, where the muscles fail to coordinate during evacuation, and that will not respond to laxatives.
Irritable bowel syndrome. Bloating in IBS is driven largely by visceral hypersensitivity, meaning normal volumes of gas are perceived as painful or distending.
Carbohydrate intolerance. Among patients with functional gut disorders investigated for it, lactose intolerance has been reported in around 51% and fructose intolerance in around 60%.
Coeliac disease. Biopsy-confirmed prevalence in Europe is around 0.8%, and bloating is a common presentation. It is worth excluding with a blood test before anyone starts removing gluten from their diet, because the test becomes unreliable once gluten is withdrawn.
Abdomino-phrenic dyssynergia. This is the mechanism behind the visible distension that some patients develop without any increase in gas. In healthy people, the diaphragm relaxes and rises to accommodate gut contents while the abdominal wall tightens. In these patients the opposite happens: the diaphragm contracts and descends while the abdominal muscles relax, pushing the abdomen forward. The volume of gas has barely changed. The shape of the abdomen has changed dramatically.
Functional abdominal bloating and distension. When bloating is the dominant symptom and the criteria for IBS, constipation and dyspepsia are not met, it is diagnosed in its own right. Global prevalence is around 3.5%.
What a sensible work-up looks like
European consensus recommends a baseline set of blood tests in all patients: full blood count, CRP, TSH, glucose, HbA1c and tissue transglutaminase IgA for coeliac disease. That screens for anaemia, inflammation, thyroid disease, diabetes and coeliac disease in one step.
Beyond that, guidance from the American Gastroenterological Association is deliberately restrained. Imaging and endoscopy are advised only where there are alarm features, recent worsening of symptoms, or an abnormal physical examination. Gastric emptying studies should not be ordered routinely.
Where evacuation is difficult, anorectal physiology testing is recommended to identify a pelvic floor disorder, because that changes the treatment entirely.
A word about SIBO
Small intestinal bacterial overgrowth is frequently offered as the explanation for bloating, and the evidence behind that is weaker than the confidence with which it is usually stated.
Every diagnostic recommendation in the American College of Gastroenterology guideline on SIBO is graded as conditional, based on very low quality evidence. Breath tests, the usual method of diagnosis, have poor accuracy. Reported sensitivity for the lactulose test ranges from 31% to 68% and specificity from 44% to 100%. Agreement between breath testing and small bowel culture is around 65%.
The American Gastroenterological Association is explicit: it does not advise testing for SIBO in patients with bloating and distension unless there are clear risk factors or severe symptoms. SIBO is real, and in the right patient it is worth treating. It is not a default diagnosis for an unexplained symptom.
The red flags
These features mean bloating needs investigating rather than managing.
- Onset of symptoms after the age of 50 without appropriate previous screening
- Unintentional weight loss
- Rectal bleeding or other signs of gastrointestinal bleeding
- Unexplained iron deficiency anaemia
- A palpable abdominal mass, or an abnormal examination
- Persistent vomiting
- Chronic diarrhoea, or a sudden and sustained change in bowel habit
- Family history of gastrointestinal cancer, coeliac disease or inflammatory bowel disease
Ovarian cancer deserves a separate mention. It is the reason persistent bloating in a woman is never treated as a purely digestive symptom. UK national guidance recommends testing for ovarian cancer in any woman, particularly aged 50 or over, with persistent or frequent abdominal distension, early satiety or loss of appetite, pelvic or abdominal pain, or increased urinary urgency and frequency, particularly if these occur more than 12 times a month.
That guidance adds a point worth repeating: appropriate tests should be carried out in any woman aged 50 or over with symptoms suggesting new-onset irritable bowel syndrome, because IBS rarely presents for the first time at that age.
What actually helps
Treat the constipation first. If stool is not moving, nothing else will work. Note that lactulose and polyethylene glycol can make bloating worse in some patients, and that several prescription secretagogues have trial evidence specifically for bloating.
A low FODMAP diet, properly supervised. Both American and British guidelines recommend a trial, though both grade the evidence as very low quality. It is a three phase process: restriction, structured reintroduction, then personalisation. It is not a permanent diet, and doing it without a dietitian tends to produce unnecessarily restricted eating rather than symptom relief.
Diaphragmatic breathing, for abdomino-phrenic dyssynergia. Where the problem is the muscular response rather than the gas, retraining that response is the treatment. Biofeedback has evidence in this group.
Biofeedback, for pelvic floor dysfunction. Effective where anorectal testing has identified the problem.
Neuromodulators and psychological therapies. Low dose antidepressants used as neuromodulators reduce visceral hypersensitivity. Gut-directed hypnotherapy and cognitive behavioural therapy have evidence in this setting.
Simple measures. Reducing carbonated drinks, chewing gum, hard sweets and eating quickly reduces swallowed air. This is sensible, low cost advice rather than trial-proven treatment.
What does not help
Probiotics. The American Gastroenterological Association states directly that probiotics should not be used to treat abdominal bloating and distension. British guidance is more permissive for IBS overall while noting that no specific strain can be recommended. Either way, there is no strong evidence for bloating specifically.
IgG food intolerance blood tests. European and American allergy societies are unambiguous: testing for IgG or IgG4 against foods is not a valid diagnostic tool. These antibodies reflect normal exposure to food, not intolerance to it. The main effect of these tests is an unnecessarily restricted diet.
“Leaky gut” protocols and anti-candida regimens. Intestinal permeability is a genuine phenomenon that occurs secondary to certain diseases. It is not a standalone diagnosis, and the supplement protocols sold to treat it have no evidence base. Documented candida infection of the gut is confined almost entirely to severely immunocompromised patients, and the fungi found in stool tests are transient passengers from food and saliva rather than colonisers.
When to see a doctor
Arrange an assessment if your bloating:
- Started recently and you are over 50
- Is present most days and is not clearly linked to meals
- Is accompanied by weight loss, bleeding, anaemia or vomiting
- Comes with early satiety, meaning you feel full after very little food
- Is associated with pelvic pain or urinary symptoms, if you are a woman
- Has clearly changed in character from your usual pattern
Long-standing, fluctuating bloating that comes and goes with meals is usually functional and manageable. Bloating that is new, persistent and progressive is a different question, and it deserves an answer rather than a diet.