Bloating is one of the most common digestive complaints: a feeling of trapped wind, a tight stomach, trousers that feel snug by the end of the day. Usually harmless, it nonetheless has a variety of causes, from air swallowed while eating to the fermentation of certain sugars, constipation or a more sensitive gut. This guide covers the mechanisms, the low FODMAP diet, the role of lactose, the simple measures that help and the signs that should prompt you to see a doctor.
Key points
- Nearly 1 in 7 adults had experienced bloating in the past week, according to a survey of 88,795 Americans.
- Feeling bloated and having a stomach that actually expands are two different things: only about half of people with bloating have visible distension.
- In irritable bowel syndrome, the low FODMAP diet improves bloating more than standard dietary advice (RR 0.72).
- In women, especially over 50, persistent or frequent bloating (particularly more than 12 times a month) warrants medical advice.
Bloating or a swollen stomach: what is the difference?
Gastroenterologists distinguish between two phenomena. Bloating is a sensation: trapped wind, pressure, a feeling of fullness in the abdomen. Distension is a measurable increase in waist circumference, the kind you can see in the mirror. The two often go together, but not always: according to the US institute NIDDK, only about half of people with bloating also have distension.
This distinction matters, because a stomach that swells is not necessarily full of gas. In many people, the amount of gas is normal, but the gut perceives it more intensely or the abdominal wall reacts in an unusual way.
How common is bloating?
Very common. In a survey of 88,795 American adults published in 2023, 13.9% reported bloating in the previous 7 days, or nearly 1 person in 7. Women and people with irritable bowel syndrome (IBS) or chronic constipation were more often affected, and 58.5% of those with bloating had never sought medical care for this symptom.
More broadly, the Rome Foundation Global Study (73,076 adults in 33 countries) found at least one functional gastrointestinal disorder in 40.3% of internet survey respondents, more often in women.
What causes bloating?
Several mechanisms often combine in the same person.
Swallowed air
People swallow more air when they eat or drink quickly, chew gum, suck sweets, drink fizzy drinks, smoke or wear poorly fitting dentures. This air mainly causes belching and discomfort in the upper abdomen.
Fermentation of certain sugars
FODMAPs are carbohydrates that are poorly absorbed in the small intestine (fructans in wheat and onion, galacto-oligosaccharides in pulses, lactose, excess fructose, polyols such as sorbitol). Once they reach the colon, they draw in water and are fermented by the gut microbiota, which produces gas. In most people this fermentation goes unnoticed; in people with a sensitive gut, it triggers discomfort and bloating.
Constipation
Slow transit gives fermentation more time and traps gas. The 2023 US guidelines advise considering treatment for constipation when it accompanies bloating.
A more sensitive gut and an abdominal wall reflex
Visceral hypersensitivity makes a normal amount of gas feel painful or uncomfortable. A Spanish study revealed another mechanism: during episodes of distension, the diaphragm descends by about 12mm and waist circumference increases by about 32mm, a reflex response of the abdominal wall rather than excess gas. In these 45 patients, biofeedback training reduced waist circumference by 25mm.
The menstrual cycle and other causes
In a study of 156 healthy women, 62% reported bloating before their period and 51% during it. Less commonly, small intestinal bacterial overgrowth (SIBO) is involved; US guidelines reserve breath testing for a small group of at-risk patients.
| Likely cause | Common clues | What to explore |
|---|---|---|
| Swallowed air | Belching, discomfort in the upper abdomen | Eat slowly, limit chewing gum and fizzy drinks |
| Fermentation (FODMAPs, lactose) | Wind and bloating a few hours after certain meals | Identify trigger foods, advice from a dietitian |
| Constipation | Infrequent or difficult stools, hard stomach | Gradual increase in fibre, water, activity; medical advice if persistent |
| Hypersensitivity, abdominal wall reflex | Flat stomach in the morning, swollen in the evening, without excess gas | Diaphragmatic breathing, IBS management |
| Menstrual cycle | Bloating before or during periods | Record symptoms over several cycles |
The low FODMAP diet: who is it for and how does it work?
It is the best-studied dietary approach in IBS. A network meta-analysis of 13 randomised trials (944 patients) showed that the low FODMAP diet reduced the risk of global symptoms not improving compared with habitual diet (RR 0.67), and improved bloating or distension more than standard dietary advice (RR 0.72). The authors note that most trials were conducted in specialist settings and did not assess the reintroduction phase.
The diet has three stages: a short elimination of high-FODMAP foods, gradual reintroduction one food group at a time to identify personal triggers, then a personalised diet that is as varied as possible. US guidelines recommend that it be supervised, preferably by a dietitian, because strict elimination is not meant to last and can make the diet less varied.
Lactose: should you cut it out?
Lactose malabsorption affects around 68% of adults worldwide, but only 28% on average in Western, Southern and Northern Europe, according to a meta-analysis covering 62,910 people in 89 countries. Malabsorption does not mean intolerance: a systematic review of 36 trials concluded that 12–15g of lactose, roughly one glass of milk (one cup), is well tolerated by most adults.
It is therefore rarely useful to cut out all dairy products. Aged cheeses contain very little lactose, and yoghurt is often better tolerated than milk. For those affected, EU regulation authorises the following claim for lactase supplements (at least 4,500 FCC units, to be taken with each lactose-containing food): “Lactase enzyme improves lactose digestion in individuals who have difficulty digesting lactose”. Tolerance to lactose varies from person to person.
Which simple measures can help with bloating?
- Eat more slowly and limit chewing gum, sweets and fizzy drinks, which increase swallowed air.
- Keep moving. In a small study of 8 patients with bloating, light exercise (cycling while lying down) reduced the proportion of retained gas from 45% at rest to 24% and lessened symptoms. A walk after meals follows the same logic, although it has not been measured.
- Breathe from the abdomen. Diaphragmatic breathing is suggested by US guidelines when the stomach swells through an abdominal wall reflex.
- Regulate bowel transit by increasing fibre gradually, with enough water.
- Take stress into account, as it can heighten gut sensitivity. The role of cortisol and the ingredients studied for stress are covered in our dedicated articles.
Peppermint, probiotics, charcoal: what do studies show?
Peppermint essential oil. In a meta-analysis of 12 trials (835 patients with IBS), peppermint oil capsules improved global symptoms (RR 2.39) and pain (RR 1.78), with adverse effects comparable to placebo (9.3% vs 6.1%). These trials do not report a separate figure for bloating.
Probiotics. A meta-analysis of 53 trials (5,545 patients) could not reach a definitive conclusion: the effective species and strains remain largely uncertain. The 2023 US guidelines advise against probiotics for treating bloating. As effects are specific to each strain, we have detailed the available data for Lactobacillus gasseri and Lactobacillus reuteri.
Activated charcoal. It is one of the few ingredients with an authorised claim on this topic: “Activated charcoal contributes to reducing excessive flatulence after eating”. The claim applies to a product providing 1g of activated charcoal per serving, with the effect obtained with 1g at least 30 minutes before a meal and 1g shortly after. If you are on any treatment, ask your pharmacist for advice.
Traditional plants. Several plants are used for digestion, such as black radish, but clinical trials on bloating remain scarce. Be wary, too, of promises of quick “de-bloating”, which are as poorly supported as most detox programmes.
When should you see a doctor about bloating?
See your doctor if bloating:
- is persistent or frequent (particularly more than 12 times a month) in a woman, especially from the age of 50: the UK NICE guidelines then recommend tests, as they do for early satiety or loss of appetite, pelvic or abdominal pain, or needing to urinate more urgently or more often;
- appears in a woman aged 50 or over with symptoms suggestive of irritable bowel syndrome, since this condition rarely begins at that age;
- comes with unexplained weight loss, unusual tiredness, a change in bowel habit (constipation, diarrhoea) or abdominal pain;
- suddenly changes in character.
According to US guidelines, abdominal imaging and endoscopy are reserved for people with warning signs, recent worsening or an abnormal clinical examination.
Frequently asked questions
Why is my stomach flat in the morning and bloated in the evening?
This is very common. Successive meals, the day's fermentation and, in some people, the abdominal wall reflex described above add up. The stomach usually returns to its normal size overnight, which distinguishes distension from weight gain.
Bloating vs fat: does bloating make you put on weight?
No. Distension temporarily increases waist circumference by a few centimetres, without any additional fat mass. It can, however, give the impression of having gained weight.
Which foods cause bloating the most?
The most common culprits are high in FODMAPs: onion, garlic, wheat, pulses, certain fruits (apple, pear), milk, and polyol sweeteners (sorbitol, xylitol). Sensitivity varies from person to person, hence the value of reintroduction.
Is bloating before a period normal?
It is common: in one study, 62% of healthy women reported it before their period. Persistent or frequent bloating (more than 12 times a month), especially after 50, should however be reported to a doctor.
Can stress cause bloating?
It can make bloating worse by making the gut more sensitive to gas. US guidelines list visceral hypersensitivity among the mechanisms to address, for example with behavioural approaches.
Should you take probiotics for bloating?
The evidence does not support recommending them for this symptom, and the 2023 US guidelines advise against using them to treat bloating. If you are considering taking them, ask a healthcare professional for advice.
Conclusion
Bloating is common and, in most cases, not serious. It arises from a mix of swallowed air, fermentation of certain sugars, slow transit and a more sensitive gut, and a swollen stomach does not always contain more gas. The best-supported approaches are simple: identify trigger foods, consider a supervised low FODMAP diet if you have IBS, do not cut out lactose without good reason, keep moving and treat constipation. Bloating that is persistent, new after 50 or accompanied by warning signs warrants medical advice.
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Food supplements are not a substitute for a varied and balanced diet and a healthy lifestyle. Ask a healthcare professional for advice if you are taking medication, are pregnant or are breastfeeding.
