What are the causes of abdominal bloating?

Causes of Abdominal Bloating

Abdominal bloating stems from six major categories: dietary/malabsorptive causes (most commonly lactose and fructose intolerance), functional gastrointestinal disorders (particularly IBS and constipation), small intestinal bacterial overgrowth, motility disorders, air-related mechanisms, and serious structural diseases that must be excluded—especially ovarian cancer in women ≥50 years. 1

Dietary and Malabsorptive Causes

Carbohydrate intolerances are the most prevalent dietary causes:

• Fructose intolerance affects 60% of patients with bloating, making it the most common dietary trigger 1
• Lactose intolerance affects approximately 51% of bloating patients, caused by lactase enzyme deficiency leading to osmotic effects from undigested sugars 1
• Fructans in gluten-containing foods may be the actual culprit rather than gluten itself in patients with self-reported gluten sensitivity 2, 1
• Sucrose intolerance from enzyme deficiencies also contributes to bloating 3

Functional Gastrointestinal Disorders

IBS is the most common functional disorder causing bloating:

• Visceral hypersensitivity in IBS creates lower sensation thresholds to bowel distention, causing bloating perception even without increased gas 1
• Functional constipation causes bloating through stool retention and altered gut transit 1
• Functional bloating as an isolated diagnosis affects 3.5% of the population (4.6% in women, 2.4% in men) when Rome IV criteria are met 1

Small Intestinal Bacterial Overgrowth (SIBO)

High-risk patients for SIBO include those with:

• Chronic watery diarrhea with malnutrition and weight loss 2, 1
• Systemic diseases causing small bowel dysmotility (cystic fibrosis, Parkinson disease) 2, 1
• GI transit delay from structural diseases 2

Motility and Neuromuscular Disorders

Several motility disorders present with bloating:

• Gastroparesis should be considered in patients with nausea and vomiting alongside bloating, though symptoms do not correlate with the degree of gastric emptying delay on scintigraphy 1, 3
• Abdominophrenic dyssynergia involves inappropriate diaphragm contraction causing abdominal distention not explained by increased intestinal gas, typically worse after meals 2, 1
• Chronic idiopathic intestinal pseudoobstruction presents with bloating and requires motility studies for diagnosis 2
• Pelvic floor dyssynergia causes bloating when straining occurs with soft stool or manual assistance is needed for defecation 3

Celiac Disease and Gluten-Related Disorders

Gluten-related conditions frequently cause bloating:

• Celiac disease causes bloating with or without changes in bowel habits, requiring screening with tissue transglutaminase IgA and total IgA levels 2
• Nonceliac gluten sensitivity (NCGS) is an immune-mediated reaction where fructans in gluten-rich foods may be the actual trigger 2, 1
• Small bowel biopsy confirms celiac disease diagnosis if serology is positive, particularly when alarm symptoms are present 2

Air-Related Mechanisms

Excessive air contributes to bloating through:

• Aerophagia involves influx of air into the esophagus with swallowing, causing intestinal gas accumulation visible on abdominal X-rays 1
• Supragastric belching occurs when air flows into the esophagus then is expelled orally before reaching the stomach 1

Critical Conditions Requiring Exclusion

Life-threatening causes must be ruled out:

• Ovarian cancer presents with bloating and abdominal fullness as often the first symptoms in women ≥50 years 2, 1, 3
• Weight loss >10% suggests malabsorption, malignancy, or serious underlying disease 2, 1, 3
• Iron-deficiency anemia mandates celiac disease testing and possible endoscopy 1, 3
• Chronic pancreatitis may cause bloating with pain despite adequate pancreatic enzyme replacement 2, 3
• Helicobacter pylori infection should be considered in patients >40 years with dyspeptic symptoms and bloating, particularly in high-prevalence regions 2, 3

Pathophysiologic Mechanisms

Four interrelated factors contribute to bloating:

• Impaired reflex control of gut handling of contents leads to segmental pooling of gas or solid/liquid components 4, 5
• Altered viscerosomatic reflexes contribute to abdominal wall protrusion and objective distention even without major intra-abdominal volume increment 4, 5
• Gut hypersensitivity creates distorted perception of normal intestinal contents 6, 4
• Altered gut microbiota composition affects intestinal gas production 6, 5

Common Pitfalls to Avoid

• Do not assume gastroparesis based on symptoms alone, as bloating, nausea, and fullness do not correlate with gastric emptying delay severity 1, 3
• Do not miss ovarian cancer in women ≥50 years with new-onset bloating, as this is often the presenting symptom 2, 1, 3
• Do not ignore pelvic floor dysfunction when straining occurs with soft stool, as this suggests dyssynergia rather than simple constipation 1, 3
• Do not perform extensive imaging and endoscopy in the absence of alarm symptoms, as the yield is low 2, 3