Bloating is mostly not extra gas, and a European consensus says simethicone lacks evidence

Bloating — the sensation of abdominal fullness and discomfort — is usually not caused by an unusual amount of gas in the bowel. A European consensus published in August 2025 by the European Society of Neurogastroenterology and Motility and United European Gastroenterology states, with 95% panel agreement, that visceral hypersensitivity rather than distension of the gastrointestinal tract due to increased intraluminal gas plays a key role in the mechanism [s1].

That single statement reframes most of what is sold and said about bloating.

Two different things, routinely conflated

The consensus separates them at the outset. Abdominal distension is an objective, visible sign of increased abdominal girth. Bloating is a sensation of abdominal fullness and discomfort, which may or may not be accompanied by distension [s1].

They are also differently common. Bloating occurs in 19% of the general population and distension in 9%, and a recent worldwide study put the global prevalence of bloating at 18% [s1]. Among people with irritable bowel syndrome, prevalence rises to between 66% and 90%, and to as much as 60% in functional dyspepsia [s1]. Functional bloating and abdominal distension — the diagnosis given when these are the recurrent, predominant symptoms and do not overlap with another disorder of gut-brain interaction — affect 3.5% of the global population, with higher prevalence in women at 4.6% and between the ages of 40 and 60 [s1].

The distinction is not academic. People who report bloating without visible distension were found to have lower pain and urgency thresholds, pointing to visceral hypersensitivity as the key factor [s1].

The mechanism behind a visibly bulging abdomen

For people whose abdomen visibly swells, the consensus describes something more specific and more surprising than trapped gas.

Normally, when the volume of bowel contents increases — whether experimentally, by infusing gas into the colon, or simply by eating a meal — the diaphragm relaxes, letting the abdominal cavity expand upward, while the abdominal wall increases its postural tone [s1]. The result is accommodation without a visible bulge; the consensus recorded 100% agreement on this description [s1].

In people with disorders of gut-brain interaction, the opposite happens. The diaphragm contracts and descends while the anterior abdominal wall relaxes, pushing the contents forward and increasing girth despite only a slight increase in intestinal gas volume [s1]. This is called abdomino-phrenic dyssynergia, and the panel agreed on the description unanimously, rating the underlying evidence as low [s1]. Intercostal muscle involvement can produce a paradoxical chest wall elevation, which the consensus offers as an explanation for the shortness of breath some patients report [s1].

Its cause is not settled. The consensus notes that the underlying reason for this abnormal viscerosomatic response is not fully understood, and cites a study in healthy volunteers in which voluntary diaphragmatic contraction after a meal worsened bloating and discomfort [s1].

Imaging has repeatedly failed to find the gas that intuition expects. Recent CT and MRI studies evaluating gut contents in relation to bloating, distension and flatulence failed to identify any change in luminal volume or content distribution that could account for the symptoms [s1].

What the consensus says about testing

In the absence of alarming signs or any relevant finding, the consensus states that clinical laboratory, imaging or endoscopic tests are unnecessary [s1]. Diagnosis rests on Rome IV criteria after excluding organic disease, using physical examination, medical history and alarm features [s1]. Younger patients with symptoms stable over six months often need minimal further investigation [s1].

The alarm features the consensus lists as triggers for advanced imaging or endoscopy are new-onset anaemia, nocturnal pain, weight loss, bloody stools, severe tenderness, succussion splash, fever, vomiting, steatorrhoea, family history of gastrointestinal malignancy and new-onset diarrhoea [s1]. And then it adds a caveat almost no consumer article carries: except for anaemia, the scientific validation of this approach is limited [s1].

On microbiome testing the consensus is unambiguous. No studies have focused on the role of gut microbiome composition in the pathogenesis of functional bloating and abdominal distension, and microbiota tests do not provide definitive diagnostic or therapeutic information for the condition, so they are not recommended in managing it [s1].

What the consensus found on treatments

The Delphi process the panel used records both the level of evidence and the proportion of experts agreeing, which makes the weak spots visible.

Simethicone — the active ingredient in the most widely sold over-the-counter anti-gas products — received the statement that there is insufficient evidence to recommend it for functional bloating and abdominal distension, at 75% agreement on low-quality evidence [s1]. The consensus notes that simethicone added to polyethylene glycol for colonoscopy preparation has been shown in meta-analyses to reduce bloating, but that no study has shown an effect in the treatment of functional bloating and abdominal distension [s1].

The statement that antispasmodic agents as a group are effective was not accepted, reaching only 60% agreement [s1]. Two specific agents did clear the bar: pinaverium and otilonium bromide were described as the most effective antispasmodics for this indication, at 75% agreement on low-quality evidence [s1].

A low-FODMAP diet is effective in reducing functional bloating and abdominal distension — 80% agreement, moderate evidence, weak recommendation [s1]. This is consistent with the randomised evidence in IBS, where a network meta-analysis of 13 trials in 944 patients found the low-FODMAP diet superior to standard British Dietetic Association and NICE dietary advice for abdominal bloating or distension, with a relative risk of symptoms not improving of 0.72 (95% CI 0.55 to 0.94) [s2].

A lactose-restrictive diet, applied to the general patient population, is of limited efficacy because the symptoms are not related to lactose intolerance with or without malabsorption — 75% agreement, very low evidence [s1]. There is insufficient evidence to recommend a gluten-free diet unless the person has coeliac disease — 90% agreement [s1]. Selected probiotics may improve symptoms at 80% agreement on low evidence, with a separate statement at 90% agreement that probiotic products differ greatly from one another and results from one cannot be generalised to others [s1]. There are no encouraging data supporting prebiotics or synbiotics [s1].

The honest position

Bloating is common, it is real, and the mechanism most people assume — too much gas — is not the one the evidence supports for most patients [s1]. The interventions with the best support are dietary and are graded moderate at best, and the most-purchased over-the-counter remedy has an explicit insufficient-evidence statement against it in this indication [s1].

The consensus is also clear about where self-management stops. Bloating and distension may be associated with organic as well as functional disorders, and the diagnostic pathway runs through alarm features and exclusion of organic disease before any of the above applies [s1].

This article is informational and is not medical advice. New, persistent or worsening bloating — particularly with weight loss, bleeding, anaemia or a change in bowel habit — needs assessment by a clinician, not a supplement.

Sources

• European Consensus on Functional Bloating and Abdominal Distension — An ESNM/UEG Recommendations for Clinical Management — United European Gastroenterology Journal, 2025-08-22
• Efficacy of a low FODMAP diet in irritable bowel syndrome: systematic review and network meta-analysis — Gut, 2021-08-10