Bloating often isn’t extra gas, and CT scans point to your diaphragm

Key takeaways

• A Rome Foundation survey of 51,425 adults in 26 countries found that about 18% felt bloated at least once a week, and women reported it about twice as often as men¹.
• In a 2009 CT study, colon gas in people with functional bloating rose by only about 32 milliliters during a bad episode, roughly two tablespoons, yet their waistlines still grew².
• In many people, visible swelling comes from a reflex: the diaphragm pushes down while the front belly wall relaxes, a pattern called abdominophrenic dyssynergia⁴⁵.
• In a 2017 Spanish trial, three biofeedback sessions cut distension scores by 56%, compared with 13% in a placebo group given simethicone⁶.
• The CDC says bloating that lasts 2 weeks or longer and isn’t normal for you can be a sign of ovarian cancer and calls for a doctor’s visit¹³.

In 2009, gastroenterologists at Vall d’Hebron University Hospital in Barcelona asked 56 people with stubborn bloating to have two CT scans². One came on an ordinary day. The other came during a bad spell, when their bloating hit 4 on a 0-to-6 scale².

If trapped gas were the culprit, the second scan should have shown a lot more of it. For most patients, it didn’t. Among the 47 with functional gut disorders, meaning no structural disease, gas in the colon rose from about 79 to 111 milliliters, an extra two tablespoons or so².

Their waistlines still grew by about 2 centimeters². What had changed was position. The diaphragm, the dome-shaped breathing muscle under the lungs, had dropped about 12 millimeters, shoving the belly’s contents down and forward².

That study and the work that followed changed how specialists explain bloating. Gas matters for some people. For many others, the bigger players are touchy gut nerves and a muscle reflex you may be able to retrain.

This guide covers what’s behind bloating, how to narrow down your likely cause and which fixes have evidence. It also covers the signs that mean bloating needs a doctor.

Bloating is a feeling, and distension is something you can measure

Doctors split this complaint in two. Bloating is the sensation of fullness, pressure or trapped gas. Distension is a visible increase in the size of your belly³.

The two don’t always travel together. A 2023 review in the American Journal of Gastroenterology says that up to half the time, bloating happens with no visible swelling⁵. The same review puts occasional bloating and distension at about 40% of the general population⁵.

Weekly bloating is common, too. In the Rome Foundation Global Epidemiology Study, about 18% of 51,425 adults reported it at least once a week¹. Rates ran from 11% in East Asia up to 20% in Latin America¹. Women reported weekly bloating about twice as often as men, and it grew less common with age¹.

The Rome Foundation writes the standard criteria for gut-brain disorders. Under its current Rome IV rules, functional bloating means symptoms at least one day a week for three months, when another gut-brain disorder such as IBS doesn’t better explain them³.

Scans show the gas is usually close to normal

The 2009 study wasn’t a fluke. In 2022, researchers from the same Barcelona group pooled data on 139 patients with visible distension⁴. Tape measures confirmed that girth grew in 138 of them, so the swelling was real⁴.

Gas didn’t explain it. In 99 patients, intestinal gas stayed within 300 milliliters of their usual level⁴. CT showed the diaphragm moving down in 82 of 103 patients scanned, and muscle recordings caught the front belly wall relaxing in 73 of 76⁴.

There’s an important exception. In the 2009 study, nine patients had intestinal dysmotility, a true disorder of gut movement, and they did pile up gas². Their belly volume rose by about 1.4 liters, almost half of it gas, and their diaphragms didn’t drop².

So a few people really are overfilled. Most people with everyday bloating are not.

Sensitive gut nerves turn normal gas into discomfort

If the gas volume is normal, why does it feel so bad? One answer is visceral hypersensitivity, a turned-up sensitivity of the nerves in your gut wall. Ordinary stretching registers as pressure or pain.

Researchers have tested this by slowly pumping gas into the rectum. In a small group with IBS or functional bloating, the gas brought on pain and swelling, and the belly wall went slack instead of firming up⁵. Healthy volunteers didn’t react that way, the 2023 review reports⁵.

Expectation plays a part, too. In one study described in that review, lettuce, a food that makes very little gas, set off visible distension in patients who believed lettuce would bloat them⁵. The swelling came from uncoordinated belly-wall muscles, not from the lettuce⁵.

None of this means bloating is imaginary. It means the gut and brain are wired together, a link our article on the gut-brain axis explains. Bloating also travels with pain: in the Rome study, people with weekly belly pain had nearly three times the odds of weekly bloating¹.

A reflex between your diaphragm and belly wall

Normally, when your gut fills, the diaphragm relaxes and your organs shift up slightly to make room⁷. In abdominophrenic dyssynergia, or APD, the reflex misfires. The diaphragm tightens and pushes down, while the front belly wall lets go⁵⁷.

The result is a familiar pattern: flatter in the morning, swollen by evening. The International Foundation for Gastrointestinal Disorders (IFFGD) notes that distension usually builds over the day and eases with rest⁷.

About 93% of people in APD studies so far have been women, and no one knows how common it is overall⁵.

The best-tested fix is biofeedback, where you watch a live signal from your own muscles and learn to change it. In a 2017 trial at a Spanish referral center, 48 patients with visible distension, all but one of them women, were randomly assigned to biofeedback or a placebo⁶.

The biofeedback group had three sessions over 10 days. Activity in their rib-cage muscles fell by about 45%, and front belly-wall activity roughly doubled⁶. Distension scores dropped 56%, compared with 13% in the placebo group, which got no training and took simethicone, a common anti-gas medicine⁶.

That’s a striking result, but it comes from one small trial at one center. The method is also complex and costly, and IFFGD says it’s offered at only a few specialized centers⁷.

Five other causes worth checking

Constipation. A backed-up colon is a common driver. In the Rome study, constipation raised the odds of weekly bloating by about 75%, even after accounting for other factors¹. When bloating comes with constipation or hard-to-pass stools, the American Gastroenterological Association (AGA) advises testing to rule out a pelvic floor disorder, which biofeedback training can treat³. Our upcoming article on constipation covers the steps.

Fermentable carbohydrates. Certain carbs, called FODMAPs, add fluid and gas to the gut’s load⁵. The American College of Gastroenterology (ACG) says FODMAP foods can trigger bloating in IBS¹⁴. NIDDK, the federal digestive disease institute, lists beans, broccoli-family vegetables, foods high in fructose or lactose, and sugar-free sweets with sweeteners ending in “-ol” among common triggers⁹. Our articles on food intolerances and low-FODMAP diets explain how to test them one at a time.

Swallowed air. Gum, hard candy, fizzy drinks, straws and talking while you eat all add air⁹. NIDDK suggests eating slowly, sitting down to eat and making sure dentures fit⁹.

Your menstrual cycle. In a Canadian survey of 156 healthy women, 62% reported bloating in the five days before their period, and 51% during it¹². Women with low mood or anxiety were more likely to report several gut symptoms at once¹². It was a small clinic survey based on memory, but it suggests your cycle is worth tracking.

Small intestinal bacterial overgrowth (SIBO). Bloating is the most common SIBO symptom, but it isn’t specific to it, according to the ACG’s 2020 guideline⁸. Risk is higher after some abdominal surgeries, with motility problems such as those caused by diabetes or scleroderma, and with opioid use⁸.

Breath tests are the usual check, and their limits are real. The ACG backs them only conditionally, on very low-quality evidence. It notes that the lactulose version has drawn criticism for false positives, while the glucose version may miss overgrowth farther down the gut⁸. The AGA reserves SIBO testing for a small group of patients at risk³.

The bloating detective checklist

Use this table to match your pattern to a likely cause. It’s our own summary of the sources above, meant to guide a conversation with your clinician, not to diagnose you.

If your bloating…	A likely contributor	What to try first
Is mild in the morning and builds through the day	Diaphragm and belly-wall reflex57	The breathing routine below; ask about biofeedback36
Comes with hard, infrequent stools or straining	Constipation or a pelvic floor problem13	Treat constipation; ask about pelvic floor testing3
Follows dairy, beans, broccoli-family vegetables, fructose-rich foods or sugar-free sweets	Fermentable carbohydrates914	Smaller portions; test one food group at a time
Comes with belching, gum chewing, fizzy drinks or fast meals	Swallowed air9	Skip gum and straws; eat slowly and seated9
Peaks in the days before your period	Menstrual cycle12	Track two or three cycles before changing your diet
Started after bowel surgery, or you have diabetes, scleroderma or take opioids	Possible SIBO8	Ask a clinician whether a breath test makes sense38
Is new for you and lasts 2 weeks or more, especially with early fullness or pelvic pressure	Needs a medical check13	Book a visit before you self-treat

A 2-minute breathing routine to try

The AGA lists diaphragmatic breathing, along with gut-nerve-calming medicines called neuromodulators, as treatments for APD³. The 2023 review adds an honest caveat: the technique clearly helps belching and air swallowing, but its value for APD on its own hasn’t been proven⁵. It’s free, low-risk and quick to test.

1. Pick your moment. Try it right after a meal, when distension tends to build⁵⁷.
2. Get set. Sit upright, or lie back with your knees bent. Put one hand on your chest and one on your belly⁵.
3. Breathe in through your nose for about 4 counts. Let the belly hand rise while the chest hand stays almost still.
4. Breathe out through pursed lips for about 6 counts. As you exhale, let your lower belly draw gently in, as if snugging a belt.
5. Keep your shoulders and upper chest quiet. The biofeedback trial taught people to calm their chest muscles and firm the front belly wall, and this step borrows that aim⁶.
6. Repeat for 2 minutes, about 12 slow breaths. The 2023 review describes sessions of 30 minutes after meals, so build up if the short version helps⁵.
7. Track it. Rate your bloating from 0 to 10 before and after, every day for two weeks.

Evidence rating: Not enough evidence for bloating on its own, though experts recommend it and the risk is close to zero. Steps 3 to 5 are our adaptation of the biofeedback approach, not a tested protocol.

What helps bloating, rated

Approach	Rating	What it rests on
Biofeedback for visible distension	Promising but early	One placebo-controlled trial of 48 people at one center, plus earlier studies56
Diaphragmatic breathing on your own	Not enough evidence	Expert advice; not tested alone for APD35
Treating constipation, including pelvic floor therapy	Promising but early	Survey link; expert advice137
Short, guided low-FODMAP trial for IBS	Promising but early	Expert-backed for IBS; see our low-FODMAP article314
Gut-brain therapies or low-dose neuromodulators	Promising but early	AGA suggests them; evidence not graded3
Peppermint oil capsules	Promising but early	Eased overall IBS symptoms and pain in a 10-study review; bloating not singled out11
Antibiotics for test-confirmed SIBO	Promising but early	Conditional ACG advice on low-quality evidence8
Simethicone	Not enough evidence	Inconsistent trials; a family-physician review found no benefit for ordinary gas10
Activated charcoal	Not enough evidence	Inconsistent trials10
Probiotics for bloating	Not enough evidence	AGA advises against them, citing weak studies3

The AGA’s 2023 update is expert advice. Its authors didn’t grade the evidence, and the AGA itself says good scientific evidence for bloating treatments is lacking³.

Peppermint oil can cause heartburn, nausea and belly pain, and enteric-coated capsules lower the heartburn risk, according to NIH’s complementary health center¹¹. Check with your clinician first if you take medicines¹¹. Our upcoming article on digestive supplements covers peppermint and others in depth.

Many natural-health readers like to start with the body’s own tools before reaching for a pill. On bloating, the research backs that instinct. The most striking trial result so far came from retraining muscles, not from a drug or a supplement⁶.

The same evidence asks for honesty about remedies of every kind. Peppermint has a real track record for IBS. But no capsule, tea or powder has been shown to shrink a swollen belly the way biofeedback did.

Questions readers ask

The bottom line

Bloating is common, real and often misunderstood. For most people, scans show close to normal amounts of gas. Sensitive gut nerves, constipation, fermentable foods, swallowed air, hormones and a misfiring diaphragm reflex do more of the work.

Start by matching your pattern to a likely cause, then test one change at a time. Breathing practice is a low-risk place to begin, and biofeedback has the best trial so far for visible swelling. If bloating is new, lasts two weeks or more, or comes with warning signs, see a doctor first.

Related reading

• Your gut and brain really talk, but many mood claims started in mice
• How gut motility works, and why a cup of coffee can wake your colon like a meal
• Cooked beans are cheap and well studied, and the lectin scare applies to raw ones
• Your body makes digestive enzymes to spare, and pills help when it can’t
• The preventive care that costs you nothing, and the exceptions

Sources

1. 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. Beth Israel Deaconess Medical Center research record. research.bidmc.org
2. Accarino A, Perez F, Azpiroz F, Quiroga S, Malagelada JR. “Abdominal Distention Results From Caudo-ventral Redistribution of Contents.” Gastroenterology, 2009;136(5):1544-1551. darmzentrum-bern.ch
3. Moshiree B, Drossman D, Shaukat A. “AGA Clinical Practice Update on Evaluation and Management of Belching, Abdominal Bloating, and Distention: Expert Review.” Gastroenterology, 2023;165(3):791-800.e3. Summarized by the American Gastroenterological Association, gastro.org, and by Smith J, “AGA CPU stresses brain-gut aspects of bloating, distention and belching,” MDedge/The Hospitalist, 2023, community.the-hospitalist.org
4. Barba E, Burri E, Quiroga S, Accarino A, Azpiroz F. “Visible Abdominal Distension in Functional Gut Disorders: Objective Evaluation.” Neurogastroenterology & Motility, September 25, 2022. Autonomous University of Barcelona research portal. portalrecerca.uab.cat
5. Damianos JA, Tomar SK, Azpiroz F, Barba E. “Abdominophrenic Dyssynergia: A Narrative Review.” American Journal of Gastroenterology, 2023;118:41-45. ddd.uab.cat
6. Barba E, Accarino A, Azpiroz F. “Correction of Abdominal Distention by Biofeedback-Guided Control of Abdominothoracic Muscular Activity in a Randomized, Placebo-Controlled Trial.” Clinical Gastroenterology and Hepatology, 2017;15(12):1922-1929. portalrecerca.uab.cat
7. International Foundation for Gastrointestinal Disorders. “Abdomino-Phrenic Dyssynergia (APD)” (adapted from a publication by Elizabeth Barba and Fernando Azpiroz, Vall d’Hebron Hospital, Barcelona). Updated February 3, 2026. iffgd.org
8. Pimentel M, Saad RJ, Long MD, Rao SSC. “ACG Clinical Guideline: Small Intestinal Bacterial Overgrowth.” American Journal of Gastroenterology, 2020. spg.pt
9. National Institute of Diabetes and Digestive and Kidney Diseases. “Treatment for Gas in the Digestive Tract.” Last reviewed June 2021. niddk.nih.gov
10. Bailey J, Carter NJ, Neher JO. “Effective Management of Flatulence” (FPIN’s Clinical Inquiries). American Family Physician, 2009;79(12):1098-1100. aafp.org
11. National Center for Complementary and Integrative Health. “Peppermint Oil.” Last updated May 2025. nccih.nih.gov
12. Bernstein MT, Graff LA, Avery L, et al. “Gastrointestinal Symptoms Before and During Menses in Healthy Women.” BMC Women’s Health, 2014;14:14. pmc.ncbi.nlm.nih.gov
13. Centers for Disease Control and Prevention. “Symptoms of Ovarian Cancer.” February 26, 2025. cdc.gov
14. American College of Gastroenterology. “Irritable Bowel Syndrome.” Patient information, updated February 2026. gi.org
15. National Institute of Diabetes and Digestive and Kidney Diseases. “Symptoms & Causes of Constipation.” Last reviewed May 2018. niddk.nih.gov