The Science Behind Bloating: Causes, Mechanisms, and Management

Bloating is a common gastrointestinal symptom, estimated to affect about one in six people worldwide. This article summarizes the science behind bloating – what causes it, the mechanisms involved, and how it can be managed.

What is Bloating?

Bloating refers to a sense of fullness, pressure, or distension in the abdominal region. It is often described subjectively as a feeling of gassiness, puffiness, or distension in the belly.

Importantly, bloating is a symptom – it does not necessarily involve objective distension or enlargement of the abdominal area. Many people experience bloating without significant measurable changes to abdominal girth.

Prevalence and Impact

Bloating is very common, reported by around 15-30% of people worldwide. It is particularly prevalent in those with functional bowel disorders like irritable bowel syndrome (IBS), affecting over 80% of IBS patients.

For those affected, bloating can negatively impact quality of life and emotional wellbeing. It is often cited as one of the most bothersome symptoms by IBS patients. Severe bloating can also potentially impair physical functioning.

Causes of Bloating

There are several potential causes of bloating:

Gas Production and Retention

Excess gas production and/or impaired gas transit through the gut are common causes of bloating. Intestinal gas comes from:

  • Swallowed air: Air swallowing when eating or drinking carbonated beverages introduces nitrogen and oxygen.
  • Diffusion from blood: Gases like carbon dioxide can diffuse from the bloodstream into the gut.
  • Bacterial fermentation: Bacteria in the colon produce hydrogen, carbon dioxide, and methane gas as they ferment undigested carbohydrates.

Certain poorly absorbed short-chain carbohydrates known as FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) are a major source of this bacteria-produced gas.

If gas transit through the intestines is impaired, gas can accumulate and cause distension. This may be due to motility disorders like IBS that slow intestinal contractions.


Accumulation of intestinal fluids, as seen in conditions like ascites or advanced liver disease, can physically distend the abdomen. This is less common than gas-related bloating.


Impaction with stool in severe constipation, or rarely obstruction by foreign material, can also distend the abdomen. Again this is not the most common cause.

Abdominal Wall Relaxation

In healthy people, the abdominal muscles automatically contract to compensate when intra-abdominal pressure increases, keeping abdominal girth constant.

In some people with bloating, this response is impaired – the abdominal muscles relax rather than contract. This allows any increase in intestinal gas/fluid to physically expand the abdomen outwards.

Mechanisms of Bloating

Several inter-related mechanisms underlie the symptom of bloating:

Increased Intestinal Gas Volume

As outlined above, excess gas production from fermentation of FODMAPs and impaired gas transit can increase the volume of intestinal gas.

This increased volume within the confined space of the abdomen increases intra-abdominal pressure. Like a balloon inflating, the abdomen may distend outwards.

Diaphragm Displacement

The diaphragm separates the abdomen from the chest cavity. As the volume of intestinal gas increases, pressure on the diaphragm may push it upwards into the chest.

This can be perceived as chest tightness or shortness of breath, and lead to an outwards increase in abdominal girth.

Abdominal Wall Relaxation

Rather than contracting to resist increased intra-abdominal pressure, some individuals relax their abdominal muscles. This allows the abdomen to bulge outwards, increasing girth.

Simultaneously, the diaphragm descends into the abdomen with the relaxed abdominal muscles. This further contributes to distension.

Visceral Hypersensitivity

Many with IBS also have heightened gut sensitivity. Even small amounts of intestinal gas or distension may be perceived as bloating.

The threshold at which distension is sensed is lowered, so bloating occurs with smaller increases in abdominal volume.

Managing Bloating

There are several approaches to managing bothersome bloating:

Dietary Modification

Avoiding foods high in poorly absorbed FODMAPs can help reduce bacterial fermentation and gas production. Common high-FODMAP foods include beans, wheat, onions, and dairy.

Eating slowly and minimizing air swallowing may also help. Carbonated drinks introduce gas, so limiting intake of these can help too.

Probiotics and Antibiotics

Altering the intestinal microbiome may reduce gas production from fermentation. Probiotic supplements can potentially accomplish this by displacing gas-producing bacteria species.

For those with an overgrowth of fermenting bacteria in the small intestine, a short course of antibiotics to ‘reset’ the microbiome may help.

Pharmacological Treatments

Medications that speed up intestinal transit, like laxatives and pro-motility agents, can aid gas passage and reduce bloating. Antispasmodics may also help by smoothing muscle contractions.

Psychological Treatments

Relaxation techniques and cognitive behavioral therapy can help ‘re-train’ abdominal muscular responses to distension. This aims to reduce abnormal relaxation of the abdominal wall.

Combination Approach

A multimodal approach combining dietary changes, microbiome modulation via probiotics, motility-modifying agents, and psychological techniques often works best for stubborn bloating.

Conclusion: Gas Production, Muscular Responses and Gut Sensitivity

Bloating is a very common but often enigmatic symptom. Multiple interacting mechanisms related to gas production, muscular responses, and gut sensitivity underlie it.

A combination of dietary changes, pharmacological treatments, and psychological techniques tailored to the individual offers the best chance of relief in persistent bloating. Further research is needed to better understand and manage this complex phenomenon.

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