Intestinal gas and flatulence: what is normal, and what isn't?
So why does this become a problem? Because in some people gas doesn't pass easily: it causes tension, bloating and cramps, the abdomen becomes distended into a “pregnant-looking shape” by evening, and passing wind becomes uncomfortably frequent or foul-smelling. This article is about that: where gas comes from, what increases it (or makes you feel you have more of it), when a disease may be hiding behind it, what you can do at home — and which signs mean that it is time for a medical examination rather than another diet.
Key point
Intestinal gas symptoms rarely mean that you “have more gas than other people”. Measurements show that people troubled by bloating often produce just as much gas as healthy people — the difference is that their intestines tolerate it less well and move it along more slowly. That is why the solution isn't simply to stop eating certain foods, but also to regulate bowel movement, posture, eating speed and — when needed — the gut microbiota.
Where does the gas come from? Three sources, three different solutions
Intestinal gas has three sources, and it matters which one applies to you, because each requires a different response. Click the tabs:
Each swallow sends a few millilitres of air into the stomach. Anyone who eats hurriedly, talks while eating, drinks through a straw, chews gum, smokes or wears ill-fitting dentures may swallow several litres of air a day. Most leaves by belching, but some continues into the bowel. Swallowed air is typically nitrogen and oxygen and is odourless — if your main symptoms are frequent belching and odourless, “loud” flatulence, this is probably where you should look for the cause. Carbonated drinks belong here too: a glass of soda water or beer sends decilitres of carbon dioxide into the stomach.
Anything not absorbed in the small intestine — fibre, certain sugars, leftover starch and some lactose — reaches the colon, where hundreds of bacterial species ferment it. The products are hydrogen, carbon dioxide, methane in some people, and small amounts of sulphur compounds, which are responsible for the smell. An estimated 30–150 grams of indigestible carbohydrates reach the colon each day; after a bowl of bean stew, this amount and gas production both rise sharply. The process itself is healthy — the microbiota that consumes fibre protects the bowel wall — and the difference lies only in the amount and in individual tolerance.
This is the least familiar factor, although it is the main one in most people with chronic bloating. Researchers in Barcelona have measured for years what happens when a known amount of gas is introduced into the bowel: a healthy bowel moves and expels the gas quickly, whereas the bowel of someone who complains of bloating holds it back and reacts painfully even to a small amount. A strange reflex also plays a part: normally, when gas collects in the bowel, the diaphragm relaxes upwards and the abdominal wall tightens, so the abdomen doesn't bulge. In many people with bloating, the opposite happens — the diaphragm pushes down and the abdominal wall relaxes — so the abdomen visibly protrudes without containing more gas. That is why someone may have a “six-month pregnant” abdomen in the evening even though the amount of intestinal gas is normal.
Which foods cause a lot of gas — and why?
Gas production is individual: what causes a “concert” in one person after bean stew may do nothing in another. There is, however, a well-known group — short-chain, fermentable carbohydrates, collectively called FODMAPs — whose effect is more predictable. The small intestine absorbs these poorly or not at all, so they reach the bacteria in the colon.
| Group | What does it include? | Why does it cause gas? |
|---|---|---|
| Legumes | Beans, lentils, chickpeas, soya beans | Raffinose and stachyose — sugars that humans have no enzyme to break down; only bacteria do |
| Cruciferous vegetables | Cabbage, Brussels sprouts, broccoli, cauliflower, Savoy cabbage | Raffinose and sulphur-containing compounds — these are also responsible for the characteristic smell |
| Onions and wheat | Onions, garlic, leeks, large amounts of wheat-based baked goods | Fructans — one of the most common hidden sources of gas, because onions are in almost every cooked dish |
| Lactose | Milk, cream, soft cheeses, ice cream | Lactose — in people with too little lactase enzyme, it reaches the colon undigested |
| Excess fructose | Apples, pears, mangoes, honey, agave syrup, fructose-sweetened soft drinks | The small intestine's ability to absorb fructose is limited; any excess ferments |
| Polyols | Sorbitol, xylitol, mannitol, maltitol — “sugar-free” chewing gum, sweets and diabetic confectionery; naturally: plums, cherries, mushrooms | They are barely absorbed; larger amounts can also cause diarrhoea |
| Fibre-rich “healthy” foods | Bran, wholegrain products, oat bran, psyllium husk introduced suddenly | Useful, but if you start eating a lot from one day to the next, the microbiota cannot keep up |
| Carbonated drinks | Soda water, soft drinks, beer, sparkling wine | Not fermentation, but direct introduction of gas — a source of belching |
Two things are worth noting. First: fatty, heavy food doesn't produce gas, but it slows stomach emptying, so it also causes tension and fullness — many people experience this as “gas”. Second: this isn't a list of forbidden foods. Legumes, cabbages and wholegrain cereals are among our most valuable foods; the aim isn't to eliminate them, but to adjust portions, preparation (soaking and thoroughly cooking beans, for example, significantly reduces the amount of gas-producing sugars) and gradual adaptation.
When might a disease be behind increased gas production?
If bloating and excessive gas have lasted for weeks, aren't clearly linked to food, or are accompanied by other symptoms (diarrhoea, constipation, weight loss or pain), it is worth considering the following conditions. Some can be ruled out or confirmed with simple tests — blood tests, a breath test or stool tests — so it is important not to try to “diet away” persistent symptoms on your own. Open the one that interests you:
In most adults, production of the lactase enzyme decreases after childhood — this isn't a disease, but a genetically determined state; it is less common in Europe, but still affects one person in every five or six. Undigested lactose ferments in the colon: bloating, gas, cramps and often diarrhoea 30 minutes–2 hours after drinking milk. It can be assessed with a hydrogen breath test. Most people affected don't need to avoid all dairy: hard cheeses, yoghurt, lactose-free products and lactase enzyme tablets help, and the severity of symptoms depends greatly on the amount consumed at one time.6
The most common functional bowel disorder: the structure of the bowel is intact, but its movement and sensation are disturbed. Abdominal pain or discomfort that changes with bowel movements, bloating, diarrhoea and/or constipation — typically worse with stress and lack of sleep. People with IBS have particularly poor gas tolerance: the same amount of gas causes much more discomfort. It doesn't increase the risk of colorectal cancer, but it can persistently reduce quality of life. A low-FODMAP diet, peppermint oil capsules, certain probiotics and stress management can all help — moderately on their own, and more when combined.2,3,5,8
Coeliac disease is an autoimmune condition: gluten (the protein in wheat, barley and rye) damages the villi of the small intestine, causing malabsorption. Its symptoms vary widely — bloating, diarrhoea, fatty stools, weight loss, iron-deficiency anaemia, fatigue and poor growth in children — but it can also cause almost no symptoms. It can be screened for with a blood test (tTG-IgA antibody), and this is very important: do not stop eating gluten before the test, because the result may then be falsely negative. If confirmed, the only treatment is a strict lifelong gluten-free diet.9 There is also a milder, non-autoimmune form in which gluten (or rather the fructans in wheat) causes bloating without coeliac disease — this is often actually FODMAP sensitivity.
Normally, few bacteria live in the small intestine and fermentation takes place in the colon. If bacteria also “move into” the small intestine — because of slow bowel movement, diabetes, abdominal surgery, long-term use of acid-reducing medicines or a bowel narrowing — food starts fermenting there: severe bloating soon after meals, diarrhoea and sometimes vitamin B12 deficiency. It may be suspected with a breath test and can be managed with antibiotics and treatment of the underlying cause. Despite the online “SIBO trend”, genuine SIBO is much less common than self-assessment suggests — suspicion must be supported by testing.
The most commonly forgotten cause. If stool remains in the colon for days, bacteria continue to ferment it and gas cannot pass around it: tension, a hard abdomen and foul-smelling wind, followed by sudden relief when the bowel finally empties. Too little fluid, too little exercise, suppressing the urge to open your bowels and certain medicines (iron supplements, opioid painkillers and some blood-pressure and allergy medicines) all slow the bowel. Gastroparesis also belongs here: delayed stomach emptying, often as a complication of diabetes, which causes early fullness, nausea and upper abdominal tension.
These are tissue-damaging inflammatory conditions, not functional disorders. Bloating is a secondary feature here: the main symptoms are persistent, often bloody or mucous diarrhoea, abdominal pain, weight loss, fever, night-time bowel movements and fatigue. They most commonly begin in young adults. A stool inflammatory marker (calprotectin) can distinguish them well from IBS, and the diagnosis can be confirmed by endoscopy. Effective treatments are now available and can achieve long-term remission — but only if the condition is recognised in time.
Reflux disease with heartburn and acid regurgitation, and stomach ulcers caused by Helicobacter pylori, mainly cause fullness and belching in the upper abdomen. Anyone who swallows frequently because of reflux (saliva neutralises acid) also swallows more air. Gallstones and reduced pancreatic enzyme production impair fat digestion: fatty, shiny, difficult-to-flush stools and post-meal tension. All these conditions can be investigated and treated; long-term use of acid-reducing medicines may itself increase intestinal gas because the antibacterial effect of stomach acid is reduced.
Many medicines are known to cause bloating as a side effect: metformin (for diabetes), acarbose, lactulose and fibre laxatives, antibiotics (which alter the gut microbiota), non-steroidal anti-inflammatory drugs, some antidepressants and opioid painkillers. Among food supplements, high-dose vitamin C, magnesium, iron supplements and protein powders (especially whey-based products in people with lactose intolerance, and those sweetened with polyols) are frequent culprits. If the symptoms started after a new product was introduced, this is an important clue.
What can you do at home? Twelve steps, in order
The order of the steps below is deliberate: it starts with the simplest changes, without side effects and effective for most people, and ends with more targeted options. Give each step 1–2 weeks and keep a diary: what you ate, when, and when the symptoms appeared — this is the cheapest and most accurate “test” you can carry out on yourself.
| Step | What should you do? | Who benefits most? |
|---|---|---|
| 1. Eat more slowly | Eat sitting down, taking at least 20 minutes, chew thoroughly and talk little while eating. No straws, less chewing gum and no cigarettes. | People who belch or pass frequent, odourless wind — reducing swallowed air |
| 2. Cut out carbonation | Remove all carbonated drinks (soda water, soft drinks and beer) for two weeks. Surprisingly often, this is enough on its own. | Upper abdominal tension and belching |
| 3. Increase fibre gradually | If you have just switched to wholegrain foods, bran, oats or psyllium husk: halve the portion, then increase it every 1–2 weeks. Drink enough alongside it. | People who have recently started “eating healthily” |
| 4. Be smart with legumes | Soak beans and lentils for 8–12 hours, discard the soaking water and cook them until soft in fresh water; start with a small portion. Rinsing tinned beans also helps. | “Concerts” after bean stew |
| 5. Move after meals | Take an easy 10–20-minute walk after every main meal. The bowel's gas-clearing movement measurably improves with gentle exercise.4 | Everyone — especially people with sedentary work or bloating |
| 6. Posture and diaphragmatic breathing | Don't lie down after eating; do 5–10 minutes of abdominal (diaphragmatic) breathing each day and sit with your back straight. The “abdominal reflex” can be trained: allowing the diaphragm to move upwards reduces visible protrusion. | People whose abdomen becomes “pregnant-looking” by evening despite a normal amount of gas |
| 7. Address constipation | Drink enough fluid, set a regular time for bowel movements (after breakfast), use a footstool at the toilet and exercise; if needed, take an osmotic laxative after consulting a doctor. | Infrequent, hard stools and a tight abdomen |
| 8. Test for lactose | Try a lactose-free period for two weeks, then deliberately reintroduce lactose (one glass of milk on an empty stomach). If the reaction is clear: choose lactose-free products and hard cheeses, and take a lactase enzyme tablet with dairy foods.6 | Cramps and diarrhoea appearing 30 minutes–2 hours after dairy products |
| 9. Try a low-FODMAP diet | For 4–6 weeks, strictly limit fructans, lactose, high-fructose fruit, polyols and legumes, then reintroduce them group by group. Do this with help from a dietitian — without support, the diet can easily become unbalanced.3 | Suspected IBS or persistent bloating not resolved by the steps above |
| 10. Enzymes | Take an alpha-galactosidase enzyme preparation from a pharmacy with legume or cabbage dishes: it breaks down raffinose in the small intestine, so less reaches the bacteria.7 | People who don't want to give up beans or cabbage |
| 11. Try a probiotic for a set period | Use one product for 4 weeks and keep a diary. If you notice no improvement, stop — there is no point taking it for months “just in case”.5 | IBS or symptoms after antibiotics |
| 12. Peppermint oil and simeticone | Enteric-coated peppermint oil capsules for IBS cramps and bloating (use caution with reflux, as peppermint relaxes the lower oesophageal sphincter). Simeticone is harmless, but the evidence is weak — you can try it, but don't expect a miracle.8 | Crampy, IBS-type symptoms |
What not to do
Don't eliminate five food groups at once, because then you'll never find out which one was responsible — and you will impoverish your gut microbiota, which can worsen gas tolerance in the long term. Don't take activated charcoal for long periods: the evidence is weak, and it also binds your medicines. Don't try “bowel cleansing” or “parasite cleansing” courses — their laxative effect may provide temporary relief, but they don't solve the problem and can damage the gut microbiota. And don't treat yourself for months if the symptoms don't improve: after a properly completed 4–6-week trial, the next step is a doctor, not another internet diet.
When should you not experiment at home? Red flags
Intestinal gas on its own is almost never dangerous. Alongside the signs below, however, bloating may not be a “gas problem” but a symptom of another disease — this is when you need a medical examination rather than a diet or pharmacy remedies:
- Bloody, black (tarry) or mucous stools – a source of bleeding in the gastrointestinal tract; black stools suggest an upper-tract source, while fresh blood suggests a lower-tract source. Don't wait for weeks.
- Unintentional weight loss and persistent loss of appetite – unintentional weight loss of more than 5% over 3–6 months together with bloating requires exclusion of malabsorption, inflammatory bowel disease or cancer.
- New, persistent symptoms beginning after age 50 – especially if bowel habits have changed (new constipation, diarrhoea or thin stools): colonoscopy is indicated, even when it seems to be “only bloating”.
- Night-time symptoms, fever or anaemia – IBS and dietary gas symptoms settle at night; anything that wakes you from sleep or is accompanied by fever, pallor or laboratory evidence of iron deficiency raises suspicion of organic disease.
- Continuously increasing abdominal girth and a tense abdomen that does not settle in the morning – this may not be gas but fluid in the abdominal cavity (ascites), which can indicate liver, heart or cancer-related disease; in women over 40, ovarian disease must also be excluded. I wrote about this separately: Ascites – when the abdomen swells from fluid, not gas →
- Crampy abdominal pain with vomiting, and complete cessation of passing wind and stools – suspected bowel obstruction (ileus): seek emergency medical care or call an ambulance immediately. No laxative or home “gas remedy” should be used in this situation.
- Colorectal cancer, coeliac disease or inflammatory bowel disease in a close family member – if a first-degree relative is affected, “just bloating” is enough reason for screening.
What will the doctor ask and examine?
First, the history: how long it has been happening, when, after what, and how it relates to food, bowel movements and stress — so it is worth bringing your diary. The doctor will then examine your abdomen, followed by basic tests: full blood count, inflammatory markers, coeliac antibodies and thyroid tests, plus faecal calprotectin and occult blood. If needed, an abdominal ultrasound, lactose or SIBO breath test, and endoscopy when red flags are present. Most people receive reassuring news: there is no structural disease, the symptoms are functional, and the twelve steps above are the treatment. In a minority, however, testing identifies something that should not have been managed for months with dietary experiments.
What does the research say? Based on readers' questions
“Do I really have more gas than other people, or am I simply more sensitive?”
Researchers in Barcelona measured this precisely: they observed thirty people who complained of excessive gas and twenty healthy people on their usual diets, followed by three days on a specifically gas-producing diet. The people with symptoms passed wind an average of 22 times during the day, compared with 7 times among the healthy participants — but the amount of gas produced after a standard meal was practically identical in the two groups (262 and 265 ml). On the gas-producing diet, both groups became more gaseous (44 and 22 episodes of flatulence respectively), but the microbiota of the symptomatic group also became “unstable”: species diversity decreased, and bacterial groups appeared whose numbers correlated with the number of episodes. The lesson: the problem is not more gas, but poorer gas tolerance and a less stable gut microbiota.1 The same research group also showed that people with bloating retain almost half of the gas introduced into the bowel while at rest, but only a quarter during gentle movement — and their symptoms decrease as a result.4
“Does the FODMAP diet work, or is it just a trend?”
It works — in the right setting. A 2022 network meta-analysis compared data from 944 people with IBS across 13 randomised trials: the low-FODMAP diet ranked first for every outcome studied — overall symptoms, abdominal pain, bloating and bowel habits — and was also better at reducing bloating than conventional advice to “eat regularly and reduce fat and caffeine”.3 Two qualifications are important, however. Most studies took place in specialist clinics under the guidance of a dietitian, and almost none examined the reintroduction phase — even though the point of the diet isn't permanent restriction, but finding out after 4–6 weeks which 1–2 groups cause problems for you. Anyone who remains in the strict phase for months may impoverish their gut microbiota and be worse off in the long term.
“Is it worth taking probiotics for bloating?”
The latest large review analysed data from 10,332 people with IBS across 82 studies. The result is sobering: some strains (for example, certain Escherichia and Lactobacillus strains) may have a moderate effect on overall symptoms, while others (Bifidobacterium, Saccharomyces) may help abdominal pain — but the certainty of evidence specifically for bloating is “very low”, and there are major differences between strains. There were no more side effects than with placebo.5 In practical terms: probiotics don't do any harm, and they help some people, but we cannot predict in advance who will benefit — which is why a four-week trial with a diary makes sense, while taking them for months “just in case” does not. I wrote separately about natural sources — sauerkraut, yoghurt and kefir: The health effects of sauerkraut →
“Are enzyme tablets useful, or are they just a waste of money?”
There is usable evidence for two enzymes. Alpha-galactosidase was tested in a double-blind, placebo-controlled study alongside 420 grams of cooked beans: the higher dose measurably reduced exhaled hydrogen (a marker of gas produced in the bowel) and the severity of flatulence, while even the lower dose reduced the overall symptom score.7 Regarding lactase enzyme, a 2019 review in Gut states that both a low-lactose diet and lactase replacement help people with lactose intolerance, but the effect is “modest” — because lactose is only one of the poorly absorbed carbohydrates, and people sensitive to lactose are often sensitive to the others too.6 There is no meaningful evidence for other “digestive enzyme complexes”. There is evidence for peppermint oil capsules, however: among 835 patients in 12 studies, the chance of improvement in IBS symptoms was more than twice that with placebo, without significant side effects.8
Frequently asked questions
In a healthy adult, 10–25 times a day is typical, and more on a high-fibre diet. Measurements show that people who complain of excessive gas pass wind more than 20 times during the day, and more than 40 times on a gas-producing diet. The number alone, however, is not a sign of disease: if you pass wind 30 times a day without discomfort, nothing needs to be done; if you pass it 10 times with pain, it does.
99% of intestinal gas is odourless (nitrogen, hydrogen, carbon dioxide and methane). The smell comes from the remaining 1% of sulphur compounds, which bacteria produce from proteins and sulphur-containing foods (eggs, meat, cabbage, onions and beer). Foul-smelling wind is therefore usually a sign of high protein and sulphur intake or constipation (longer fermentation) — not disease. If the smell changes and is accompanied by fatty stools, weight loss or diarrhoea, however, it may indicate malabsorption.
It isn't dangerous, but regularly doing so isn't advisable. Held-in gas doesn't disappear: some is absorbed through the bowel wall and leaves through the lungs (which is why it can sometimes be noticed on the breath), while the rest comes out later anyway. Persistent retention causes tension, cramps and louder bowel sounds, and creates the bad habit of learning to ignore your bowel's signals — which can also lead to problems with constipation. Find a toilet and don't hold it in.
This is classic functional abdominal bloating and, according to measurements, often involves not more gas but reversed movement of the diaphragm and abdominal wall (the diaphragm pushes down and the abdominal wall relaxes). Spreading food intake across the day into smaller portions, avoiding carbonation and polyols, walking after meals, diaphragmatic breathing and — if present — treating constipation can help. What does not fit the picture is an abdomen that does not settle in the morning and grows week by week — that may be fluid, so see a doctor.
Yes, and it isn't “just in your head”. The autonomic nervous system controls bowel movement and sensation: under stress, sympathetic dominance slows the bowel and increases pain sensitivity, while at rest the parasympathetic (vagus nerve) system drives digestion. In some people with IBS, relaxation, gut-directed hypnotherapy and regular sleep are as effective as diet. Read more about the connection between the gut and the nervous system: The parasympathetic nervous system and chronic diseases →
In infants, gas and “colic” result from immature bowel movement and swallowing air while feeding, and usually resolve by 3–4 months; tummy massage, winding and bicycle movements with the legs can help. In older children, carbonated drinks, fruit juice (fructose!), sugar-free gum and sweets (sorbitol) are the most common causes. Take your child to a doctor if bloating is accompanied by poor growth, persistent diarrhoea, fatty stools, bloody stools or recurrent abdominal pain — these are warning signs of coeliac disease and inflammatory bowel disease in childhood.
Summary – Quick overview
Sources
- Manichanh C, Eck A, Varela E, et al. Anal gas evacuation and colonic microbiota in patients with flatulence: effect of diet. Gut. 2014;63(3):401-408. DOI: 10.1136/gutjnl-2012-303013
- Lacy BE, Cangemi D, Vazquez-Roque M. Management of Chronic Abdominal Distension and Bloating. Clin Gastroenterol Hepatol. 2021;19(2):219-231. DOI: 10.1016/j.cgh.2020.03.056
- 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
- Villoria A, Serra J, Azpiroz F, Malagelada JR. Physical activity and intestinal gas clearance in patients with bloating. Am J Gastroenterol. 2006;101(11):2552-2557. DOI: 10.1111/j.1572-0241.2006.00873.x
- Goodoory VC, Khasawneh M, Black CJ, Quigley EMM, Moayyedi P, Ford AC. Efficacy of Probiotics in Irritable Bowel Syndrome: Systematic Review and Meta-analysis. Gastroenterology. 2023;165(5):1206-1218. DOI: 10.1053/j.gastro.2023.07.018
- Misselwitz B, Butter M, Verbeke K, Fox MR. Update on lactose malabsorption and intolerance: pathogenesis, diagnosis and clinical management. Gut. 2019;68(11):2080-2091. DOI: 10.1136/gutjnl-2019-318404
- Di Stefano M, Miceli E, Gotti S, Missanelli A, Mazzocchi S, Corazza GR. The effect of oral alpha-galactosidase on intestinal gas production and gas-related symptoms. Dig Dis Sci. 2007;52(1):78-83. DOI: 10.1007/s10620-006-9296-9
- Alammar N, Wang L, Saberi B, et al. The impact of peppermint oil on the irritable bowel syndrome: a meta-analysis of the pooled clinical data. BMC Complement Altern Med. 2019;19(1):21. DOI: 10.1186/s12906-018-2409-0
- Rubio-Tapia A, Hill ID, Semrad C, et al. American College of Gastroenterology Guidelines Update: Diagnosis and Management of Celiac Disease. Am J Gastroenterol. 2023;118(1):59-76. DOI: 10.14309/ajg.0000000000002075
