What causes abdominal bloating? 7 specific causes

What causes abdominal bloating?

Abdominal bloating usually comes from a specific biochemical imbalance that keeps producing or trapping gas, and in chronic cases it can bring abdominal pain and sometimes diarrhea along with the discomfort. In the clinics where I work as a scientific collaborator, the same complaint keeps leading back to very different triggers.

Bloating is the feeling of trapped gas, pressure or fullness. Distension is a measurable increase in waist size. The two often travel together, but they can also appear on their own, and that difference matters when you look for the cause.⁹

The misplaced air mystery

At first glance, it might seem that bloating after eating comes from food sitting in your stomach. The cause usually sits deeper. The bloat you feel is rarely swallowed air that travels straight down into your belly. Swallowed air would have to cross several meters of gut first, and in adult cadavers the small and large intestine together measured close to 8 meters on average.¹⁰

Instead, most of it comes from processes deep in your digestive system. Gas produced inside, especially between the angled colonic flexures, is the usual culprit. Chronic bloat of this kind is a signal that the gut's natural fermentation is off, and many people try home remedies without ever finding out which cause is behind it. The step-by-step mechanism, from the first bite to the flexures, is explained in bloating and gas after eating.

Why do I look pregnant when I bloat?

Many people with functional bloating have no more gas inside than anyone else. Their belly swells because of how the muscles around it react. In a CT study of 47 patients with a functional bowel disorder, total abdominal volume rose by only about 0.3 liters during a severe bloating episode, while the front wall pushed out and the diaphragm moved down.²

When researchers added the same colonic gas load to patients and healthy volunteers, the patients developed clearly more distension, with a paradoxical contraction of the diaphragm.¹¹ Breathing-focused biofeedback reduced diaphragm activity and brought the girth down by about 25 mm on average in a small group of 15 patients.³ That is why diaphragmatic breathing appears in the American Gastroenterological Association advice for this pattern.⁸

7 specific causes of abdominal bloating

The response to bloating treatment, even within the same diagnosis of IBS, differs completely from one patient to the next. It all comes down to different biochemistries. Here are seven examples, each with a different trigger behind the same symptom.

Post-infectious bloating

After an infection or a course of antibiotics, the balance in your digestive system is disturbed. This dysbiosis can lead to a buildup of gas and even diarrhea. Across 45 studies, more than 10% of people developed IBS within a year of an infectious enteritis, and antibiotic use during the infection raised the odds.⁴ If you were sick recently and the bloat lingers, your gut bacteria may still be recovering. Read the post-infectious IBS case and viral versus bacterial post-infectious IBS.

Post-cholecystectomy bloating

After gallbladder removal, fat digestion changes. This can lead to poor fat absorption and a belly that fills with gas, often with abdominal pain. It is a specific biochemical response to a disrupted digestive process, and portion size plays a smaller part. The effect varies from person to person, and in one prospective study clear new diarrhea in the months after the operation was rare.¹² Read the post-cholecystectomy IBS case and IBS after gallbladder removal.

After contracting Pseudomonas from a pet

Believe it or not, a pet can be the suspected source in some cases seen in practice. Pseudomonas aeruginosa turned up in 46 of 47 people with IBS in one stool study, against 10 of 30 healthy controls, and higher numbers went with abdominal distension.¹³ It was also more common in duodenal brushings of IBS patients.¹⁴ Its elastase loosened the tight junctions between epithelial cells in cell cultures, so it may irritate the duodenal lining and keep inflammation going.¹⁵ The bloat here comes from the bacteria, with swallowed air playing no real part. Read the Pseudomonas-predominant IBS case and Pseudomonas high in stool.

If you have Proteus and take glutamine

In laboratory work, excess L-glutamine was a strict requirement for Proteus mirabilis to swarm, its fast-spreading form.¹⁶ A glutamine supplement may therefore help Proteus spread in a gut where it is already high, and the bloat can come with constipation and abdominal pain. In such cases the quality of the fermentation matters more than the amount you eat. Read the Proteus-predominant IBS case and can glutamine cause diarrhea.

After taking PPIs for a long time

Long-term use of proton pump inhibitors has been linked to small intestinal bacterial overgrowth. In a meta-analysis of 11 studies the odds of SIBO were about twice as high in PPI users, and the link was clearest when SIBO was diagnosed by culture of intestinal fluid.⁵ A later analysis of 19 studies found a moderate increase.¹⁷ With less stomach acid the environment shifts, and the gas and bloating that follow can become a real source of pain. Read the PPI and IBS case and PPIs and vitamin B12.

Chronic late-night eating, SIBO-IBS

Regular late meals can disrupt normal stomach emptying. In healthy men, solid food left the stomach about 54% more slowly at 8 PM than at 8 AM.¹⁸ Food that lingers may give bacteria more time to ferment, and the bloat that leaves you overly full can turn into chronic bloating that keeps coming back. Read the SIBO case and is snacking bad for digestion.

If you have diabetes

In people with diabetes, exocrine pancreatic insufficiency can lead to poor digestion. A review estimated moderate insufficiency in 30% to 50% of people with type 1 diabetes and 15% to 35% with type 2.⁶ Undigested food then ferments, which causes gas, bloating and abdominal discomfort, and over time weight loss rather than gain. Read the IBS and diabetes case and symptoms of fat malabsorption.

These are only some of the possible causes. Although bloating is the shared symptom in every scenario above, the biochemical trigger differs. To resolve bloating, you first need to recognize the specific trigger behind it. Without that, treatment tends to chase the symptom, and long-term relief stays out of reach.

Infographic

1. 1

   After an infection

   More than 10% of people developed IBS within a year of an infectious enteritis across 45 studies.

   
2. 2

   Gallbladder removal

   Fat digestion changes after the operation. This can lead to poor fat absorption and a belly that fills with gas.

   
3. 3

   Long-term PPIs

   Long-term PPI use has been linked to small intestinal bacterial overgrowth. The odds of SIBO were about twice as high in users.

   
4. 4

   Late-night meals

   Late meals can disrupt stomach emptying. In healthy men, solid food left the stomach about 54% more slowly at 8 PM than at 8 AM.

   
5. 5

   Diabetes and the pancreas

   In diabetes, exocrine pancreatic insufficiency can lead to poor digestion. Undigested food then ferments and causes gas and bloating.

   

Sources: Klem et al. 2017, Lo and Chan 2013, Goo et al. 1987, Capurso et al. 2019.

gutpathways.com

Save this infographicImage 4:5, with sources, from gutpathways.com

The same symptom can have very different causes in different people, which is also the case for IBS overall. I explain this in what causes IBS in different people.

Individual variability and anatomical causes of bloating

No two bodies are exactly alike. How bloating shows up depends on personal traits and even on anatomy. For instance, a dolichocolon may trap gas more easily, which makes the bloat both uncomfortable and persistent.

Dolichocolon

An inborn variant in which the colon is longer than usual, with extra loops, often at the flexures or in the sigmoid. Reported frequency ranges from 1.9% to 28.5%.¹⁹

Studies of the redundant colon describe a triad of constipation, abdominal pain and distension. More redundancies were linked with a longer colon transit time, and with more pain, bloating and infrequent bowel movements.¹⁹ When you feel bloated low in the abdomen in a way that seems unique to you, part of the answer may sit in this kind of physiology.

Why do women bloat more?

Hormonal fluctuations, especially in women, can add to bloating. Studies of healthy women found a slower gut transit in the luteal phase of the cycle, and women with IBS often report more abdominal pain, bloating or diarrhea around menstruation.²⁰ Women were also more likely to report bloating in the large US survey.¹ A cyclical pattern points to hormones as one layer, though it rarely explains the whole picture alone.

Diagnosing and managing abdominal bloating

Finding relief starts with a clear diagnosis. You have probably asked yourself how to get rid of a bloated belly, or whether bloating can cause shortness of breath. These questions need a personal approach, because the same answer will not fit two different causes.

Comprehensive medical, lifestyle and dietary history

It all begins with a detailed review of your medical history. When the bloat appears, whether it follows certain foods such as lactose or other foods linked to intolerance, and whether constipation or diarrhea come with it, all give useful clues. Past infections, antibiotics, surgery, long-term medicines and meal timing belong in the same history.

Targeted testing and analysis

Next comes targeted testing. Tests for specific bacterial populations, enzyme deficiencies, small intestinal bacterial overgrowth or lactose intolerance can reveal the cause, alongside the clinical criteria for IBS. The choice should follow the evidence.

• ▲ Rome IV criteria for primary bloating and distension.⁸
• ▲ Dietary restriction or breath testing for carbohydrate intolerance, and aspirate or breath testing for SIBO in selected people.^{8, 21}
• ▲ Blood tests for celiac disease.⁸
• ▲ Imaging or endoscopy only with alarm features, recent worsening or an abnormal examination.⁸

Personalized management strategies

Managing bloating then needs a plan built around the cause. Diet adjustments, antimicrobials, probiotics and other interventions may help relieve bloating when they match the cause. Probiotics are a debated choice: the AGA expert review advises against using them for bloating and distension on their own.⁸

When is abdominal bloating a warning sign?

Most bloating is functional, but some patterns need a doctor first. Recent, frequent bloating together with a growing abdomen deserves attention. In one study of women presenting to primary care, bloating raised the odds of ovarian cancer about 3.6-fold and an increase in abdominal size about 7.4-fold, and the combination of bloating, a larger abdomen and urinary symptoms appeared in 43% of the women with cancer against 8% of clinic patients.⁷

How to relieve bloating?

Your bloat can be traced back to very specific causes, from post-infectious dysbiosis and the changes after a cholecystectomy to long-term PPI use or late-night eating. Understanding the cause is the first step toward a remedy that works for you.

Remember, bloating is a signal from your body that something in your stomach and gut needs attention. In practice, effective management comes from addressing the underlying cause, whether that means adjusting your diet or restoring balance in your digestive system. For meal-specific triggers, see how to match digestive enzymes for bloating to the food behind it.