Bloating is often the IBS symptom people find most bothersome. In one study, people with every IBS subtype reported far more bloating than healthy controls, and 48% had measurable swelling beyond the normal range.[1] Research has turned up a surprise: people with IBS generally don't make extra gas. The problem is how the gut senses and moves normal amounts of gas, and sometimes how the belly muscles respond to it.[2][3][4]
Bloating vs distension: what's the difference?
Bloating is a feeling: trapped gas, pressure or fullness. Distension is a visible, measurable increase in waist size. They often happen together but can occur separately.[5] In IBS, the feeling and the actual swelling matched closely only in people with constipation-predominant IBS, who also had the most distension.[1]
Why is my stomach so bloated with IBS?
- FODMAPs are fermented. Some carbohydrates aren't absorbed in the small intestine. In MRI studies, fructans such as inulin reached the colon and filled it with gas, while fructose drew water into the small intestine.[6] FODMAPs are fermentable oligo-, di-, monosaccharides and polyols.
- The gut is oversensitive. After an inulin drink, people with IBS produced about the same amount of gas as healthy people but had more symptoms. The researchers concluded that hypersensitivity to stretching, not excess gas, drives the symptoms.[2]
- Gas doesn't move along well. When gas was infused into the small intestine, 18 of 20 people with IBS retained it or developed symptoms or swelling, compared with 4 of 20 controls.[3]
- The belly muscles respond the wrong way. Normally, when gas builds up, the diaphragm relaxes and the front of the belly tightens. In people with bloating, the diaphragm contracted and pushed down while the abdominal wall relaxed, so the belly pushed outward. This is called abdomino-phrenic dyssynergia.[4]
- A daily rhythm. In healthy volunteers, waist size grew over the day and after meals and shrank during sleep.[7] Because IBS amplifies how gas and stretching feel, this normal rise can be much more noticeable, so bloating often builds toward evening.
- Constipation. Distension was most prominent in IBS with constipation.[1]
Bloating also comes in waves. In a three-month diary study, bloating episodes lasted about 3.5 days on average, and bloating and pain occurred together on 59% of the days when either was present.[8]
What helps IBS bloating?
| Approach | What the evidence says |
|---|---|
| A short-term low-FODMAP diet, ideally with a dietitian | Ranked first for bloating in a network meta-analysis, and better than standard UK dietary advice for bloating.[9] The ACG recommends a limited trial,[10] and US experts advise dietitian supervision.[11] |
| Swapping bran for soluble fiber | NICE advises against insoluble fiber such as bran. If you add fiber, choose soluble types such as ispaghula (psyllium) or oats; oats and linseeds may help wind and bloating.[12] In a trial, people taking bran dropped out early most often, mainly because their symptoms got worse.[13] |
| Treating constipation | US experts suggest constipation treatments for bloating when constipation is present, and tests for a pelvic floor problem when emptying is difficult.[11] |
| Diaphragmatic breathing or biofeedback | Recommended for abdomino-phrenic dyssynergia.[11] In a randomized trial, biofeedback training of the belly and chest muscles reduced the feeling of distension by 56%, compared with 13% on placebo.[14] |
| Gut–brain treatments | Central neuromodulators (such as low-dose antidepressants) and psychological therapies such as hypnotherapy and CBT may be used for bloating and distension.[11] |
| Peppermint oil | Better than placebo for overall IBS symptoms and pain, though the evidence is very low quality and side effects were more common. The analysis looked at overall symptoms and pain, not bloating specifically.[15] |
| Probiotics | US experts advise against using them to treat bloating and distension.[11] |
The low-FODMAP diet is meant to be short-term, followed by reintroduction to find your personal triggers. Get professional advice first if you have, or have had, an eating disorder, if you're pregnant, or before using it for a child.
What should you track?
Note how bloated you feel, whether your belly actually looks swollen, the time of day, what you ate in the hours before, and your stool type. If bloating builds every evening, look at lunch and dinner rather than only the last thing you ate. A food and symptom diary makes these patterns easier to see, and our guide to common IBS trigger foods is a good place to start. IBS Clue, an iPhone app coming soon, pairs bloating check-ins with the meals you log by photo or text, estimates each meal's level in the six FODMAP groups, and ranks the groups most likely to be your triggers.
When to see a doctor
- New, persistent bloating or swelling, especially if you're a woman over 40. In a UK primary-care study, abdominal distension, bloating, loss of appetite, needing to urinate more often and abdominal pain were all linked with ovarian cancer.[16]
- Alarm features: blood in your stool, weight loss you can't explain, anemia, fever, or symptoms that wake you at night.[17]
- No celiac test yet? Ask about one. US experts note that a celiac blood test can rule out celiac disease in people with bloating.[11]
Scans and endoscopy aren't routine for bloating. They're reserved for alarm features, recently worsening symptoms or an abnormal examination.[11] See also IBS red flags.