Beans, Gas, FODMAPs and Digestion
Why beans cause gas, what feeding studies found about adapting over weeks, what FODMAPs are, the low-FODMAP diet for irritable bowel syndrome, and sourced ways to ease digestion.
Content last updated . This page has not been medically reviewed.
Beans, lentils and chickpeas are famous for causing gas. This guide explains why, what two kinds of evidence say (feeding studies and gut-condition research), and which tips have a source behind them. It is information, not medical advice. If gas comes with symptoms that worry you, talk to a clinician.
Read this first
- Gas from beans is normal. The NIDDK says legumes are among foods that can cause extra gas, because some of their carbohydrates reach the large intestine undigested and gut bacteria break them down, which makes gas. [1]
- For many people it settles. In three feeding studies of about half a cup of beans a day, reports of extra gas were highest in the first one to three weeks and then fell in most groups. A minority kept noticing it. [2]
- Go slowly. Harvard Health says to eat legumes gradually at first so your gut bacteria can adapt. [3] The NIDDK advises raising fiber by about 2 to 3 grams a day. [4]
- If you have irritable bowel syndrome (IBS), Monash University lists most legumes as high in FODMAPs and says the low-FODMAP diet is best followed with a dietitian and only for medically diagnosed IBS. [5]
- Evidence in one line: adaptation over weeks is supported by small studies; the benefit of the low-FODMAP diet in IBS is mixed in pooled analyses. [2] [6]
Why beans cause gas
Beans are rich in fiber and in carbohydrates called oligosaccharides that people cannot digest well. [1] [3] Monash University describes FODMAPs as short-chain carbohydrates the gut does not fully absorb; gut bacteria ferment them and produce gas. One FODMAP group, galacto-oligosaccharides (GOS), is found in legumes and pulses, and Monash says most legumes and pulses are high in FODMAPs. [5] The NIDDK also lists whole grains, some fruits, dairy and sugar alcohols as other gas sources. [1] Legume fiber also includes soluble fiber and resistant starch, which Harvard Health says may help lower cholesterol, blood pressure and body weight. [3]What feeding studies found
One research group reports three studies in which adults ate about half a cup of beans a day for 8 or 12 weeks and filled in weekly questionnaires. [2] The studies measured how people felt, not how much gas they made. The paper's funding source was not stated on the page we read. [2]| Group | Week 1: reported more gas | Later weeks |
|---|---|---|
| Pinto beans (crossover trial) | 50% | 6% in week 2, 0% in week 3 [2] |
| Black-eyed peas | 19% | 6% by week 4 [2] |
| Vegetarian baked beans | 47% | 24% in week 2, 7 to 11% in weeks 5 to 8 [2] |
| Pinto beans (12-week parallel trial) | 45% | 23% at week 4, about 15 to 23% through week 12 [2] |
| Control foods (carrots; chicken soup) | about 3% (carrots), 0% (soup) | 0 to 8% [2] |
The authors concluded that worry about bean gas may be exaggerated, and said people vary by bean type. A steady minority were still bothered after months. They suggested starting with smaller portions or splitting servings. [2] Expectations may shape what people notice; the paper raises this as a possibility. [2]
Sourced ways to ease digestion
| Tip | What the source says |
|---|---|
| Add beans gradually | Harvard Health: bacteria adapt and produce less gas over time. [3] NIDDK: raise fiber by about 2 to 3 g a day. [4] |
| Soak dried beans and cook them in fresh water | Harvard Health says soaking overnight and cooking in fresh water helps remove gas-producing substances; soaking twice helps more. [3] |
| Canned beans | Harvard Health says canned beans skip the soaking step. [3] Whether rinsing canned beans lowers FODMAPs: we could not read Monash's testing, so we do not claim it. |
| Smaller or split servings | Suggested by the authors of the feeding studies. [2] |
| Eat slowly, avoid swallowing air | NIDDK: eat slowly, sitting down, limit gum, hard candy, fizzy drinks and straws; keep a food and symptom diary. [1] |
| Enzyme products (alpha-galactosidase) | Proper evidence not found in the sources we read. |
Soaking also changes nutrients. A 2026 review reported that soaking raised soluble fiber by up to 33% but that some phenolics and minerals leached into the soaking water. [7] See dried vs canned beans: soaking and sodium.
FODMAPs and the low-FODMAP diet in IBS
The NIDDK says a doctor may suggest a short trial of a low-FODMAP diet (reducing these foods for a few weeks, then reintroducing them to find triggers) and that beans and lentils appear among FODMAP foods. [4] Monash describes a 2 to 6 week strict phase, then a gradual loosening, and says about 3 in 4 people improve. [5]Pooled analyses are less clear. A 2025 systematic review and meta-analysis of 15 randomized trials (1,118 people) found a risk ratio of 1.21 for global symptom improvement, with a confidence interval of 0.98 to 1.51 that includes no difference, and no clear gain in quality of life. [6] A 2026 review concludes that several trials show benefit and that guidelines now include the diet as a first- or second-line option, while stressing individual tailoring. [8] Because the diet is restrictive, it is usually done with a dietitian. [5] Soluble fiber, which beans provide, appears more helpful for IBS than insoluble fiber, according to the NIDDK. [4]
We did not find a source with tested FODMAP serving sizes for specific beans that we could read, so we give none. Check the Monash app or a dietitian.
How much fiber is in cooked beans?
USDA values per 100 g of boiled beans without salt. A US adult's fiber target is 22 to 34 g a day (Dietary Guidelines, quoted by the NIDDK); the UK guideline is 30 g a day and most UK adults average about 20 g (NHS). [4] [9]| Food (cooked, no salt) | Fiber per 100 g | Per 1 cup | Source |
|---|---|---|---|
| Lentils | 7.9 g | 15.6 g (198 g) | FDC 172421 [10] |
| Black beans | 8.7 g | 15.0 g (172 g) | FDC 173735 [11] |
| Chickpeas | 7.6 g | 12.5 g (164 g) | FDC 173757 [12] |
| Red kidney beans | 7.4 g | 13.1 g (177 g) | FDC 175194 [13] |
A cup of cooked beans is a big step up from many diets, which is one reason to build up slowly. See how much fiber per day and fiber side effects.
Related pages
Frequently asked questions
Why do beans make me gassy?
Some of their carbohydrates are not digested and reach the large intestine, where bacteria ferment them and make gas. [1] Monash lists most legumes as high in FODMAPs. [5]
Will the gas go away if I keep eating beans?
In three feeding studies, reports of extra gas dropped over the first weeks in most groups, but a minority kept reporting it. [2] These were self-reported symptoms in small studies.
Does soaking beans stop gas?
Harvard Health says soaking overnight and cooking in fresh water helps remove gas-producing substances. [3] We found no trial measuring this effect, so the size of the benefit is unknown.
Should I follow a low-FODMAP diet if beans bother me?
Monash says the diet is for medically diagnosed IBS and is best done with a dietitian. [5] Pooled trials show a possible but not certain benefit. [6]
Are beans safe to eat raw or half-cooked to avoid gas?
No. Raw or undercooked red kidney beans can cause poisoning; see lectins in beans. [14]
References
- NIDDK. Eating, diet and nutrition for gas in the digestive tract. Last reviewed June 2021. Read 2026-10-24.
- Winham DM, Hutchins AM. Perceptions of flatulence from bean consumption among adults in 3 feeding studies. Nutr J 2011;10:128. Read 2026-10-24.
- Harvard Health Publishing. Legumes: are they good for your heart?. Page dated 3 August 2026. Read 2026-10-24.
- NIDDK. Eating, diet and nutrition for irritable bowel syndrome. Last reviewed November 2017. Read 2026-10-24.
- Monash University. About FODMAPs and IBS. Page footer 2019. Read 2026-10-24.
- Khan Z, Muhammad SA, Amin MS, Gul A. The efficacy of the low-FODMAP diet in irritable bowel syndrome: a systematic review and meta-analysis. 2025 (abstract read via Europe PMC). Read 2026-10-24.
- Janahar JJ, Balasubramaniam H, Zhang Y. Nutritional and functional attributes of legumes: a review of processing methods and their impacts. J Food Sci 2026 (abstract read via Europe PMC). Read 2026-10-24.
- Colecchia L et al. Nutritional management of irritable bowel syndrome. 2026 (abstract read via Europe PMC). Read 2026-10-24.
- NHS. How to get more fibre into your diet. Last reviewed 2 March 2026. Read 2026-10-24.
- U.S. Department of Agriculture. FoodData Central: Lentils, mature seeds, cooked, boiled, without salt (FDC 172421). Read 2026-10-24.
- U.S. Department of Agriculture. FoodData Central: Beans, black, mature seeds, cooked, boiled, without salt (FDC 173735). Read 2026-10-24.
- U.S. Department of Agriculture. FoodData Central: Chickpeas, mature seeds, cooked, boiled, without salt (FDC 173757). Read 2026-10-24.
- U.S. Department of Agriculture. FoodData Central: Beans, kidney, red, mature seeds, cooked, boiled, without salt (FDC 175194). Read 2026-10-24.
- U.S. Food and Drug Administration. Natural toxins in food. Read 2026-10-24.