Do prebiotics help with bloating and gas?

What reviews found

A 2019 review that measured bloating and gas pooled 11 randomized trials with 729 adults who had irritable bowel syndrome (IBS) or another functional bowel disorder. These are gut problems with no visible damage. Prebiotics were no better than placebo for bloating, flatulence, abdominal pain or quality of life.^[1] Overall response was 54% with prebiotics and 63% with placebo, a difference that was not statistically significant.^[1]

The result changed with the type and the dose:^[1]

• Doses of 6 g a day or less improved flatulence severity, but the result was at the edge of statistical significance (P = 0.05).^[1]
• Prebiotics other than inulin-type fructans improved flatulence.^[1]
• Inulin-type fructans made flatulence worse.^[1]

None of the 11 trials was at low risk of bias in every category, so these results are not firm.^[1]

Trials of low-dose GOS

Galacto-oligosaccharides (GOS) have the most encouraging trials, but they are small:^[2][3]

• 83 adults from the general population with bloating, abdominal pain or flatulence took 2.75 g of a GOS mixture (B-GOS) or placebo each day for 2 weeks, then switched. Scores for all three symptoms were lower by the end of the first week and stayed lower at the end of the second. Stool frequency, stool form, quality of life and mood did not change.^[2]
• 44 people with IBS completed a 12-week trial of 3.5 g or 7 g of GOS a day against placebo. Flatulence and bloating improved at 3.5 g. At 7 g, the trial reported better overall symptom ratings and anxiety scores, and not less bloating or flatulence.^[3]

Trials of inulin

Inulin has not reduced bloating in the trials found:^[4][5][6]

• 36 people with abdominal symptoms and poor tolerance of gut gas took 8 g of inulin or placebo a day for 4 weeks. Their daily symptoms did not change in either group. Gas retention in a lab test fell by 22% with inulin, but the difference from placebo was not statistically significant.^[4]
• A 2014 review of 5 trials with 252 people with constipation found that inulin helped bowel function but did not improve pain or bloating.^[5]
• A 2025 British guideline on constipation found no effect of inulin-type fructans on bloating, and worse flatulence in 2 trials that gave 12 g and 15 g a day.^[6]

Why the results differ

Prebiotics act on gut bacteria, and this process itself makes gas:^[7][8]

1. Bacteria in the colon ferment the prebiotic.^[7]
2. Fermentation raises the gas and volume in the colon. An MRI study showed this after a drink with 40 g of inulin.^[8]
3. People with IBS felt more symptoms from the same amount of gas as healthy people, which points to a more sensitive colon.^[8]

Dose also matters. In a trial of healthy adults, flatulence was the most common symptom after 5 g or 10 g of inulin products, followed by bloating.^[9] In the 2019 review, only doses of 6 g a day or less improved flatulence.^[1]

Products that combine a prebiotic with something else

Some positive trials did not test a prebiotic alone, so they say little about prebiotics themselves:^[10][11]

• In 350 adults with self-reported bloating or indigestion, a daily synbiotic for 6 weeks raised the share who never or rarely felt bloated: 72.3% against 55.9% with placebo. The product held a mix of probiotics and 400 mg of pomegranate extract. Seed Health sponsored the trial.^[10]
• In 60 people with diarrhea-predominant IBS, a product with xyloglucan, pea protein, grape seed tannins and xylo-oligosaccharides improved bloating over 28 days.^[11]

What is still unknown

The 2019 review covered only people with IBS or similar disorders, so its results may not apply to everyone with bloating.^[1] The trials of low-dose GOS were small and short, and the authors of the 83-person trial asked for further research.^[2]