What causes diarrhea and bloating?

Causes of Diarrhea and Bloating

The most common causes of diarrhea and bloating include food intolerances (particularly carbohydrate malabsorption), small intestinal bacterial overgrowth (SIBO), irritable bowel syndrome (IBS), and medication side effects. 1

Primary Causes

1. Food Intolerances and Malabsorption

• Carbohydrate enzyme deficiencies:

  • Lactase deficiency (lactose intolerance) - affects up to 51% of patients with digestive disorders 1
  • Fructose intolerance - more common (60%) than lactose intolerance 1
  • Sucrase-isomaltase deficiency (SID) - found in 35% of patients with presumed IBS-D/M 2

• Mechanism: Undigested sugars have osmotic effects in the colon due to malabsorption, leading to bloating, gas, and diarrhea 1, 3

2. Small Intestinal Bacterial Overgrowth (SIBO)

• Characterized by excess bacteria in the small intestine 4
• Causes bloating, distention, gas, and diarrhea through fermentation of undigested carbohydrates 3
• May coexist with other conditions like IBS 4

3. Irritable Bowel Syndrome (IBS)

• Many IBS patients identify food as a trigger for symptoms 5
• Patients with visceral hypersensitivity (common in IBS) are more likely to experience symptoms due to lower sensation thresholds in response to bowel distention 1

4. Medication-Related Causes

• Up to 4% of chronic diarrhea cases are medication-related 1
• Common culprits include:
  • Magnesium supplements
  • Antihypertensives (especially ACE inhibitors)
  • Non-steroidal anti-inflammatory drugs
  • Dipeptidyl peptidase-4 inhibitors (gliptins)
  • Antineoplastic agents
  • Theophyllines
  • Antibiotics
  • Antiarrhythmics 1

5. Therapy-Associated Causes (in Cancer Patients)

• Chemotherapy toxicity (5-Fluorouracil, irinotecan, capecitabine, anthracyclines) 1
• Antibiotic-induced disruption of gut microflora 1
• Radiation therapy involving the gastrointestinal tract 1

6. Other Important Causes

• Infectious causes: Various pathogens including C. difficile (especially after antibiotic use) 1
• Excessive alcohol intake: Direct toxic effect on intestinal epithelium, rapid gut transit, decreased activity of intestinal disaccharidases, and decreased pancreatic function 1
• Artificial sweeteners and FODMAPs: Sorbitol and other fermentable carbohydrates 1
• Systemic diseases: Thyrotoxicosis, diabetes mellitus, adrenal disease, systemic sclerosis 1
• Enteral tube feeding: GI intolerance occurs in up to 30% of enterally fed patients 1

Diagnostic Approach

1. Initial assessment:

   • Evaluate for alarm features (unexplained weight loss, persistent blood in stool, nocturnal symptoms) 1
   • Basic laboratory tests: CBC, electrolytes, liver function, vitamin B12, folate, calcium, ferritin, ESR, CRP, thyroid function 1, 6
   • Serological tests for celiac disease 1, 6

2. Specific testing for suspected causes:

   • Food intolerances: Dietary restriction trial (2 weeks) is the simplest and most economical approach 1
   • SIBO: Hydrogen/methane breath test using glucose as substrate or small bowel aspirate 3, 4
   • Stool tests: For infectious causes, including C. difficile 1

3. Advanced testing when initial workup is inconclusive:

   • Abdominal imaging (X-ray, ultrasound, CT) 6
   • Endoscopic evaluation 6
   • Specialized tests: anorectal manometry, gastric emptying studies, hydrogen breath testing 6

Management Considerations

• Food intolerances: Dietary modification with restriction of triggering carbohydrates 1
• SIBO: Antibiotics (rifaximin is most studied but expensive; alternatives include amoxicillin, fluoroquinolones, metronidazole) 1, 4
• Medication-induced diarrhea: Consider alternative medications when possible 1
• Non-infectious diarrhea: Loperamide (2 mg every 2 hours during day, 4 mg every 4 hours at night) 1, 7
  • Monitor for constipation, which occurs in 2.6% of patients with acute diarrhea and 5.3% with chronic diarrhea 7

Clinical Pearls and Pitfalls

• Diagnostic pitfall: Factitious diarrhea (laxative abuse) should be considered in cases of chronic unexplained diarrhea, especially in tertiary referral centers where it may account for up to 20% of cases 1
• Therapeutic pitfall: Treating with antibiotics without proper patient selection can lead to antibiotic resistance and further microbiome disruption 1
• Clinical pearl: The simplest way to diagnose food intolerance is a short dietary restriction trial with resolution of symptoms as a positive predictor 1
• Monitoring consideration: In patients with bloating and diarrhea who don't respond to initial therapy, consider factitious causes by checking stool for laxatives 1