Gas, distension, and the gut — separating the common from the concerning
Bloating is the sensation of fullness, pressure, or tightness in the abdomen — often described as feeling as though your belly is stretched, swollen, or full of gas. It may or may not be accompanied by visible distension of the abdomen, and the two aren't always the same thing: you can feel bloated without appearing swollen, and some people have visible distension without much discomfort.
It is one of the most common digestive complaints. Around 18% of the general population worldwide experience bloating at least once a week — and in people with irritable bowel syndrome or other gut-brain interaction disorders (conditions where the gut and brain communication is disrupted), the figure rises to between 50% and 96%.
Despite how common it is, bloating is often poorly explained. People are frequently told it's "just IBS" or "something you ate" — without a proper exploration of what's actually driving the symptom. Understanding the causes makes it possible to address the right one.
These two terms are often used interchangeably but are distinct. Bloating is a subjective feeling — the sensation of abdominal fullness or pressure. Distension refers to an objective, measurable increase in abdominal girth (the circumference around the belly). Both can occur together or independently. For clinical purposes, doctors now use the term Functional Abdominal Bloating/Distension (FABD) when symptoms are recurrent and not explained by another condition.
Bloating doesn't have a single cause — and this matters, because the right approach depends on understanding which mechanism is driving symptoms in an individual. The main causes include:
Bacteria in the colon ferment undigested carbohydrates and produce gas — mainly hydrogen, carbon dioxide, and methane. Certain foods (FODMAPs, beans, onions, cruciferous vegetables like broccoli and cauliflower) produce significantly more gas than others.
Gas is produced constantly in the gut. Problems arise when it doesn't move through efficiently. Slowed gut motility (the muscle movement that propels contents through), constipation, or altered gut muscle coordination can cause gas to accumulate and pressure to build.
Some people perceive normal amounts of gas as uncomfortable — a feature of the gut-brain axis (the two-way communication between gut and brain). The nerves supplying the gut are oversensitive, meaning small amounts of gas or movement cause disproportionate discomfort. This is common in IBS.
When bacteria normally found in the colon migrate to the small intestine, they ferment food earlier than normal, producing gas in a part of the gut less equipped to handle it. Bloating, particularly after meals, is a hallmark symptom.
Lactose intolerance (inability to digest milk sugar), fructose malabsorption (difficulty absorbing fruit sugar), and intolerance to other fermentable carbohydrates are very common. Undigested sugars reach the colon and are fermented, producing gas and bloating.
The composition of gut bacteria (the microbiome) varies between individuals and affects how much gas is produced from fermentation. Some gut bacteria produce more gas; others produce less. Diet, antibiotics, and stress all affect the microbiome.
FODMAPs are a group of short-chain carbohydrates that are poorly absorbed in the small intestine. When they reach the colon, gut bacteria ferment them rapidly — producing gas and drawing water into the gut. In people with IBS or a sensitive gut, this causes bloating, pain and altered bowel habit. The good news: it's highly food-specific, which makes it manageable once individual triggers are known.
Bloating is assessed through a combination of history, examination, and targeted investigations — not by immediately ordering a battery of tests. The clinical history is usually the most informative part of the assessment.
A good history distinguishes functional bloating (a gut-brain disorder, typically long-standing, related to food and stress) from organic causes (something structural or biochemical that warrants investigation). The GP will ask about the timing of symptoms — do they come on after eating? After specific foods? Are they constant or intermittent? Are they getting worse? Is there associated pain, change in bowel habit, or weight loss?
The relationship to food is particularly informative. Bloating that reliably comes on after dairy suggests lactose intolerance. Bloating after wheat, onions, garlic, or pulses points toward FODMAP sensitivity. Bloating that is constant and unrelated to food may suggest a different mechanism altogether.
Not everyone with bloating needs tests — but several targeted investigations are used when there is clinical reason:
| Investigation | What it checks for |
|---|---|
| Blood tests — FBC, CRP, coeliac screen (anti-tTG IgA), thyroid function | Coeliac disease, anaemia, inflammation, thyroid disorders |
| Stool tests — faecal calprotectin (a marker of gut inflammation) | Inflammation in the gut — helps distinguish IBS from inflammatory bowel disease |
| Hydrogen breath test | Lactose intolerance, fructose malabsorption, SIBO |
| Coeliac serology + small bowel biopsy | Coeliac disease — requires prior blood test confirmation |
| Pelvic ultrasound (women) | Ovarian cysts or masses when bloating is persistent and unexplained |
| Colonoscopy / CT scan | When clinically time-sensitive features are present — to exclude bowel or abdominal pathology |
Dietary approaches are first-line in most cases. NICE describes a dietitian-led low-FODMAP diet trial as the recommended pathway for IBS with bloating — temporarily restricting fermentable carbohydrates, then systematically reintroducing foods to identify individual triggers. It is not a permanent diet.
Lactose exclusion is simple and effective when lactose intolerance is confirmed or strongly suspected — even before formal testing. A 2–4 week dairy-free trial followed by careful reintroduction is a reasonable first step.
Addressing constipation matters — slow gut transit and stool buildup significantly worsen bloating. Adequate fibre, hydration, and activity are first-line; laxatives may be needed short-term.
Medications used for bloating include antispasmodics (mebeverine [Colofac], hyoscine [Buscopan]) for gut spasm, low-dose antidepressants (which modulate gut-brain signalling — amitriptyline is commonly used), and specific treatments for SIBO (rifaximin [Xifaxanta] antibiotic) where this is confirmed. Simethicone and activated charcoal preparations are sold over the counter but have limited evidence for bloating specifically.
Gut-directed hypnotherapy and CBT (cognitive behavioural therapy) have good evidence for functional gut disorders including bloating — particularly when there is significant gut-brain axis involvement or coexisting anxiety.
The largest global study of bloating to date used data from the Rome Foundation Global Epidemiology Study — an internet survey of 51,425 individuals across 26 countries, including the UK. It found that nearly 18% of the general population reported bloating at least once per week. Women were approximately twice as likely as men to report bloating (23.4% vs 12.2%). Prevalence decreased with age, was more common in Latin America than East Asia, and was strongly associated with abdominal pain. The authors noted that bloating is significantly underscreened in both primary care and gastroenterology.
Ballou S, Singh P, Nee J, et al. Prevalence and Associated Factors of Bloating: Results From the Rome Foundation Global Epidemiology Study. Gastroenterology 2023;165(3):647–655.e4. DOI: 10.1053/j.gastro.2023.05.049
This randomised, controlled crossover trial from Monash University in Australia is the landmark study establishing the low-FODMAP diet as an effective treatment for IBS symptoms including bloating. Thirty IBS patients and eight healthy controls were randomly assigned to 21 days on a low-FODMAP diet or a typical Australian diet. Patients on the low-FODMAP diet had significantly lower overall symptom scores and specifically reduced bloating, pain, and passage of wind. This was high-quality evidence — a controlled crossover design with strictly provided food — and formed the basis for subsequent guideline adoption.
Halmos EP, Power VA, Shepherd SJ, Gibson PR, Muir JG. A diet low in FODMAPs reduces symptoms of irritable bowel syndrome. Gastroenterology 2014;146(1):67–75.e5. DOI: 10.1053/j.gastro.2013.09.046
A Gut 2022 systematic review and network meta-analysis identified 13 eligible RCTs (944 patients) comparing a low-FODMAP diet with various comparator interventions in IBS. The low-FODMAP diet ranked first for all endpoints studied — including global IBS symptoms, abdominal pain severity, and abdominal bloating/distension severity. It was superior to habitual diet (relative risk of symptoms not improving 0.67) and superior to BDA/NICE dietary advice specifically for bloating (relative risk 0.72). This is the most up-to-date synthesis of the dietary evidence.
Black CJ, Staudacher HM, Ford AC. Efficacy of a low FODMAP diet in irritable bowel syndrome: systematic review and network meta-analysis. Gut 2022;71(6):1117–1126. DOI: 10.1136/gutjnl-2021-325214
A 2025 survey of 516 UK adults (predominantly women, mean age 38) found that 86% had experienced gastrointestinal symptoms in the previous month. Bloating was reported by 64% — making it the second most common symptom after flatulence — and was identified as the most anxiety-provoking symptom, causing more worry than heartburn or abdominal pain. Notably, 72% of respondents had no diagnosed gastrointestinal condition, demonstrating how prevalent bloating is across the general population, not just in those with established gut disorders. Dairy foods and fatty foods were most commonly linked to bloating in this cohort.
Tuck C, Barrett J, Sherwin S, Gibson PR. Prevalence of gastrointestinal symptoms in the UK adult population and perceived effects of foods. European Journal of Nutrition 2025. DOI: 10.1007/s00394-025-03780-0
Bloating is extremely common — but common doesn't mean it has to be put up with. The research is clear that in most cases there is an identifiable driver, whether that's FODMAP sensitivity, lactose intolerance, constipation, IBS, or SIBO — and that targeted management produces real, meaningful improvement.
Dietary approaches, particularly dietitian-led low-FODMAP, have the strongest evidence base. But the right approach depends on the right diagnosis first — which is why persistent bloating is a conversation for you to have with your GP or healthcare professional, rather than something to leave unexplored indefinitely.
New, persistent, worsening bloating — or any alarm features — is clinically recognised as time-sensitive. In UK practice, 111 or urgent GP access exists for exactly this.
This article is health education, not medical advice. It is intended to help you understand bloating and the evidence around it — not to replace a consultation with your own doctor. Anything personally relevant — symptoms, existing conditions, or treatment decisions — is a conversation for you to have with your GP or healthcare professional.