Understanding Feces: Composition, Normal Variation, and Clinical Significance

Feces (stool) is the solid waste eliminated from the body after digestion and nutrient absorption. It provides valuable insight into digestive health.

Composition

• Water: ~75% (varies with hydration and fiber)
• Solid matter (~25%):
  • Undigested fiber (cellulose, etc.)
  • Dead and live bacteria (~30% of dry weight)
  • Inorganic salts
  • Fats and nitrogenous compounds
  • Mucus and sloughed intestinal cells
  • Bile pigments (stercobilin gives brown color)

Normal Characteristics (Bristol Stool Scale)

• Type 3–4: Ideal—sausage-shaped, smooth or cracked surface, easy to pass
• Frequency: 3 times/day to 3 times/week
• Color: Brown (from stercobilin); variations with diet (green from leafy vegetables, red from beets, black from iron/bismuth)
• Odor: Characteristic, from bacterial metabolism (indole, skatole, hydrogen sulfide)

Factors Influencing Bowel Movements

• Diet: Fiber, fluid intake, fat, artificial sweeteners
• Hydration: Dehydration hardens stool
• Medications: Opioids, antacids, antibiotics, iron supplements
• Medical conditions: IBS, IBD, thyroid disorders, diabetes
• Lifestyle: Exercise, stress, routine

Red Flags Requiring Medical Evaluation

• Persistent change in frequency or consistency (>2 weeks)
• Blood in stool (bright red or tarry black)
• Unexplained weight loss
• Severe abdominal pain
• Pencil-thin stools
• Clay-colored or pale stools