What causes gas and bloating after eating in an adult with no significant medical history?

Gas and Bloating After Eating: Causes and Evaluation

Gas and bloating after eating in healthy adults most commonly result from carbohydrate intolerances (particularly fructose and lactose), functional gastrointestinal disorders like IBS, or dietary factors that increase intestinal fermentation. 1, 2

Primary Causes to Consider

Carbohydrate Intolerances (Most Common)

• Fructose intolerance affects 60% of patients with bloating, making it the most prevalent dietary cause 1, 2
• Lactose intolerance occurs in 51% of bloating patients, caused by lactase enzyme deficiency leading to osmotic effects from undigested sugars 1, 2
• Not all individuals who malabsorb carbohydrates develop symptoms—those with visceral hypersensitivity (like IBS patients) are more likely to experience bloating due to lower sensation thresholds 1
• The simplest diagnostic approach is a 2-week dietary restriction trial, with symptom resolution serving as a positive predictor 1, 2

Functional Gastrointestinal Disorders

• Irritable bowel syndrome (IBS) commonly presents with bloating due to visceral hypersensitivity, where patients have abnormally low thresholds for sensing bowel distention 2, 3
• Functional dyspepsia causes gastric bloating through disordered motility and delayed gastric emptying 3
• Functional constipation produces bloating through stool retention and altered gut transit 2
• These disorders are characterized by disordered motility and visceral hypersensitivity often worsened by psychological distress 3, 4

Gluten and Fructan Sensitivity

• In patients with self-reported gluten sensitivity, fructans in gluten-containing foods may be the actual culprit rather than gluten itself 1, 2
• Celiac disease, nonceliac gluten sensitivity, and gluten intolerance all cause bloating with or without bowel habit changes 1
• Tissue transglutaminase IgA and total IgA levels should be checked to screen for celiac disease, particularly if alarm symptoms are present 1, 2

Small Intestinal Bacterial Overgrowth (SIBO)

• High-risk patients include those with chronic watery diarrhea, malnutrition, weight loss, and systemic diseases causing small bowel dysmotility (e.g., cystic fibrosis, Parkinson disease) 1, 2
• SIBO results from decreased gastric acid secretion and declined intestinal motility 1
• Diagnosis uses hydrogen-based breath testing with glucose or lactulose, or small bowel aspirates 1, 2

Air-Related Mechanisms

• Aerophagia involves influx of air into the esophagus with swallowing, causing intestinal gas accumulation visible on abdominal X-rays 1, 2
• Supragastric belching occurs when air flows into the esophagus then is expelled orally before reaching the stomach 1, 2
• Eating quickly, chewing gum, and carbonated beverages increase air swallowing 1

Motility Disorders

• Gastroparesis should be considered in patients with nausea and vomiting alongside bloating 2
• Abdominophrenic dyssynergia involves inappropriate diaphragm contraction causing abdominal distention not explained by increased intestinal gas, typically worse after meals 1, 2
• Chronic idiopathic intestinal pseudoobstruction can present with bloating and distention 1

Diagnostic Approach Algorithm

Step 1: Assess for Constipation

• If constipation is present, evaluate for IBS with constipation or chronic constipation using Rome IV criteria 1
• Consider anorectal manometry to diagnose pelvic floor dyssynergia 1

Step 2: Evaluate for Food Intolerance

• Start with a 2-week trial eliminating suspected carbohydrates (lactose, fructose, fructans) 1, 2
• If dietary restriction fails, consider breath testing for lactose, fructose, or sucrose intolerance 1

Step 3: Screen for Alarm Symptoms

• Alarm symptoms include: vomiting, weight loss >10%, GI bleeding, family history of IBD, or recent worsening nausea/pain 1
• If present, perform motility studies to diagnose gastroparesis or other motility disorders 1
• In women ≥50 years, bloating and abdominal fullness may be presenting symptoms of ovarian cancer 1, 2

Step 4: Assess SIBO Risk Factors

• If high-risk features present (chronic diarrhea, malnutrition, systemic diseases), consider hydrogen-based breath testing or small bowel aspirates 1, 2

Step 5: Consider Structural Abnormalities

• If no clear cause identified, consider CBC, CMP, KUB, abdominal ultrasound, or CT/MRI to exclude structural abnormalities 1
• Upper endoscopy may be considered in patients >40 years with dyspeptic symptoms, especially in regions with high Helicobacter pylori prevalence 1

Critical Pitfalls to Avoid

• Do not assume gastroparesis based on symptoms alone—bloating, nausea, and fullness do not correlate with the degree of gastric emptying delay on scintigraphy 2
• Do not miss ovarian cancer in women ≥50 years presenting with new-onset bloating and abdominal fullness 1, 2
• Do not ignore pelvic floor dysfunction—straining with soft stool or need for manual assistance suggests dyssynergia, not just constipation 2
• In the absence of alarm symptoms, the yield of clinically meaningful findings from extensive testing is low 1

Pathophysiologic Mechanisms

Gas and bloating occur through multiple mechanisms 5, 6:

• Excess gas production from carbohydrate malabsorption and intestinal fermentation 5, 4
• Altered gas transit through the GI tract due to motility disorders 5, 7
• Abnormal perception of normal gas volumes due to visceral hypersensitivity 5, 4
• Dysfunctional somatic muscle activity in the abdominal wall causing visible distention 4, 7