A 48-year-old woman from Bangalore undergoes laparoscopic cholecystectomy for gallstones. Postoperatively, she develops chronic diarrhea and fat malabsorption. Her fecal fat is 8 g/day (normal < 7 g/day). Serum albumin and prothrombin time are normal. Pancreatic enzymes and glucose are normal. Abdominal imaging shows no obstruction. Which of the following best explains her fat malabsorption?

Explanation

## Post-Cholecystectomy Fat Malabsorption: Bile Acid Metabolism ### Normal Bile Acid Physiology **Key Point:** The gallbladder is a **storage and concentration organ**, not a synthesis organ. Bile acids are synthesized in the liver and stored in the gallbladder. ### Enterohepatic Circulation of Bile Acids 1. **Synthesis:** Liver produces ~0.5 g bile acids daily 2. **Storage:** Gallbladder concentrates and releases bile acids with meals 3. **Reabsorption:** 95% of bile acids are reabsorbed in the **terminal ileum** via active transport 4. **Recycling:** Reabsorbed bile acids return to the liver via portal blood (enterohepatic circulation occurs 6–8 times daily) 5. **Fecal loss:** Only ~0.5 g/day is lost in stool (replaced by new synthesis) ### Post-Cholecystectomy Changes Without a gallbladder: - Bile acids are released **continuously from the liver** rather than in concentrated pulses with meals - The **terminal ileum receives dilute bile** and cannot reabsorb bile acids efficiently - **Fecal bile acid loss increases** (up to 1.5–2 g/day) - The liver cannot synthesize bile acids fast enough to replace the loss - **Net reduction in bile acid pool** → reduced micelle formation → **fat malabsorption** **Clinical Pearl:** Post-cholecystectomy diarrhea and steatorrhea occur in 10–15% of patients due to increased colonic bile acid reaching the colon, which stimulates secretion and increases motility. ### Why Pancreatic Function Is Normal - Pancreatic lipase secretion is **stimulated by CCK**, which is released by fat and amino acids in the duodenum - CCK secretion is **independent of the gallbladder** - Pancreatic enzyme output remains normal post-cholecystectomy - The problem is **bile acid availability**, not enzyme secretion | Feature | Normal | Post-Cholecystectomy | |---------|--------|---------------------| | Bile acid synthesis | 0.5 g/day | 0.5 g/day (unchanged) | | Bile acid reabsorption | 95% in terminal ileum | Reduced due to dilute bile | | Fecal bile acid loss | 0.5 g/day | 1.5–2 g/day | | Bile acid pool size | ~3.5 g | ~2–2.5 g | | Fat absorption | Normal (micelle formation adequate) | Impaired (reduced micelle formation) | **High-Yield:** Post-cholecystectomy steatorrhea is due to **reduced bile acid pool**, not pancreatic insufficiency. [cite:Guyton and Hall 13e Ch 64; Harrison 21e Ch 297]