What causes belly bloating?

What Causes Belly Bloating?

Belly bloating results from multiple mechanisms including food intolerances (especially lactose, fructose, and FODMAPs), visceral hypersensitivity, abnormal gut-brain interactions, small intestinal bacterial overgrowth (SIBO), constipation with retained stool, and abdominophrenic dyssynergia (abnormal diaphragm and abdominal wall muscle coordination). 1, 2

Primary Mechanisms

Food Intolerances and Carbohydrate Malabsorption

• Carbohydrate enzyme deficiencies (lactase, sucrase) and artificial sweeteners (sugar alcohols, sorbitol) are among the most common dietary triggers 1, 2
• Fructose intolerance is particularly prevalent, affecting 60% of patients with digestive disorders, while lactose intolerance affects 51% 1
• Undigested sugars create osmotic effects in the colon due to malabsorption, but symptoms only occur in those with visceral hypersensitivity 1
• FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) trigger bloating through fermentation and gas production 1, 2

Gluten and Fructans

• Patients with celiac disease, non-celiac gluten sensitivity (NCGS), and gluten intolerance experience bloating with or without bowel habit changes 1
• In many self-reported gluten-sensitive patients, fructans in gluten-rich foods rather than gluten itself cause the symptoms 1, 2

Visceral Hypersensitivity and Gut-Brain Dysfunction

• Visceral hypersensitivity means lower sensation thresholds in response to bowel distention, making normal amounts of gas feel uncomfortable 1, 3
• This is particularly common in irritable bowel syndrome (IBS), where brain-gut interactions are disrupted 1, 2, 3
• Approximately 10-25% of healthy persons experience bloating, but it's far more common in those with functional gastrointestinal disorders 4, 5

Constipation and Pelvic Floor Disorders

• Retained stool load with colon distention causes bloating, especially in IBS with constipation (IBS-C) and chronic constipation 1
• Dyssynergic defecation (pelvic floor dyssynergia) leads to constipation and bloating through visceral hypersensitivity and retained stool 1
• Straining even with soft stool, need for digital disimpaction, or splinting suggests pelvic floor dysfunction 1, 2

Small Intestinal Bacterial Overgrowth (SIBO)

• SIBO causes bloating through bacterial fermentation of carbohydrates in the small intestine 1, 2, 6
• High-risk patients include those with chronic watery diarrhea, malnutrition, weight loss, and systemic diseases causing small bowel dysmotility (cystic fibrosis, Parkinson's disease) 1, 2

Abdominophrenic Dyssynergia

• Abnormal abdominal-phrenic reflexes involve inappropriate diaphragm contraction and abdominal wall muscle relaxation 1, 6, 3
• This creates visible abdominal distention not explained by increased intestinal gas, typically worse after meals 1, 3

Motility Disorders

Gastroparesis and Functional Dyspepsia

• Approximately 40% of gastroparesis patients report bloating that correlates with nausea, fullness, and pain—but NOT with the degree of gastric emptying delay 1
• Functional dyspepsia (FD) and gastroparesis (GP) may represent the same spectrum of gastric neurodysfunction 1
• Severe constipation is present in >30% of patients with severe gastroparesis symptoms and relates to delayed small bowel and colonic transit 1

Intestinal Dysmotility

• Altered gut motility impairs gas handling and transit, contributing to bloating 6, 3
• Patients with refractory upper GI symptoms, severe bloating with weight loss, or suspected intestinal neuromyopathic disorders may need specialized motility testing 1

Other Contributing Factors

Altered Gut Microbiota

• Dysbiosis (imbalanced gut bacteria) contributes to bloating through altered fermentation patterns 6, 3

Aerophagia

• Excessive air swallowing can cause intestinal gas accumulation visible on abdominal X-rays 1

Structural and Systemic Causes

• Chronic pancreatitis may cause bloating with pain despite adequate pancreatic enzyme replacement 1
• Ovarian cancer often presents with bloating and abdominal fullness, especially in women ≥50 years 1, 2
• Recent weight gain and weak abdominal muscles contribute to the sensation of bloating 4, 5

Important Clinical Considerations

The American Gastroenterological Association emphasizes that bloating is multifactorial, requiring an algorithmic diagnostic approach based on associated symptoms, alarm features, and risk factors rather than extensive testing in all patients. 1, 2

Key Pitfall to Avoid

• Not all patients who malabsorb carbohydrates develop symptoms—only those with visceral hypersensitivity (like IBS patients) experience bloating from normal amounts of undigested sugars 1
• The simplest diagnostic approach is a 2-week dietary restriction trial before pursuing expensive breath testing or other investigations 1, 2