Does stool smell differ after bowel resection surgery?

Does Stool Smell Change After Bowel Resection Surgery?

Yes, stool odor typically changes after bowel resection surgery, primarily due to bile acid malabsorption (affecting >80% of patients with ileal resection), small intestinal bacterial overgrowth (occurring in ~30% of patients), and fat malabsorption—all of which produce volatile compounds and metabolic byproducts that alter stool smell. 1

Primary Mechanisms Causing Odor Changes

Bile Acid Malabsorption (Most Common)

• Bile acid malabsorption occurs in more than 80% of patients following ileal resection and is the leading cause of altered bowel function and stool characteristics after surgery. 2, 1
• When bile acids are not reabsorbed in the terminal ileum, they reach the colon where colonic bacteria metabolize them into volatile compounds that produce characteristic odor changes. 1
• Resections as short as 5 cm of terminal ileum can trigger bile acid malabsorption and subsequent odor alterations. 1
• The unabsorbed bile acids contribute to diarrhea and steatorrhea (fatty stools), which have characteristically different and often more offensive odors than normal stool. 1

Small Intestinal Bacterial Overgrowth (SIBO)

• SIBO occurs in approximately 30% of patients after bowel resection, particularly when the ileocecal valve is removed, causing symptoms of bloating, diarrhea, nausea, and altered stool odor. 2, 1
• Loss of the ileocecal valve allows retrograde movement of colonic bacteria into the small intestine, nearly doubling the prevalence of bacterial overgrowth. 1
• These bacteria ferment nutrients that would normally be absorbed, producing hydrogen and methane gases plus metabolic byproducts that distinctly alter stool odor. 1
• The altered microbial composition following surgery includes increased abundance of Bacteroides, Parabacteroides, and Ruminococcus species, which promote intestinal inflammation and change fermentation patterns. 3

Fat Malabsorption and Steatorrhea

• Fat malabsorption occurs when more than 60-100 cm of terminal ileum has been resected, as hepatic bile salt synthesis cannot compensate for the loss of ileal reabsorption surface area. 2, 1
• Unabsorbed fatty acids in the colon are metabolized by bacteria, producing short-chain fatty acids and other compounds that contribute to characteristic foul-smelling stool. 1
• Steatorrhea produces distinctly malodorous stools due to bacterial fermentation of unabsorbed fats. 1

Long-Term Microbiome Changes

• Bowel resection induces long-term changes in the gut microbial community that persist for months to years after surgery. 4
• Surgical bowel preparation combined with perioperative antibiotics causes substantial shifts in bacterial composition, with greater abundances of Enterococcus, Lactobacillus, and Streptococcus that can take 31 days or longer to begin recovering toward baseline. 5
• Patients who develop postoperative complications show significantly stronger reductions in microbial diversity starting 6 months after operation, which does not resolve even after 24 months, contributing to persistent odor changes. 6

Clinical Red Flags Requiring Investigation

If stool odor changes are accompanied by any of the following symptoms, systematic evaluation for bile acid malabsorption and SIBO is warranted: 1

• Diarrhea (particularly nocturnal diarrhea, which is never normal after surgery) 1
• Weight loss or malnutrition 2, 1
• Bloating or abdominal distension 2, 1
• Nausea or vomiting 2
• Steatorrhea (greasy, floating stools) 1

Diagnostic Approach

• Consider faecal calprotectin testing to distinguish inflammatory recurrence (in Crohn's disease patients) from non-inflammatory causes like bile acid malabsorption or SIBO. 1
• A therapeutic trial of bile acid sequestrants is appropriate as first-line investigation, particularly if faecal calprotectin is not significantly raised, rather than immediately pursuing expensive testing. 2
• SeHCAT scanning should only be requested when there is diagnostic uncertainty, as it is often abnormal after ileal resection or with ileal inflammation, and an abnormal scan does not prove that symptoms are due to bile salt malabsorption. 2
• Lactulose breath testing measuring hydrogen and methane can diagnose SIBO when clinical suspicion is high. 2

Treatment Approaches

For Bile Acid Malabsorption

• Therapeutic trial of bile acid sequestrants (cholestyramine, colestipol, or colesevelam) is recommended as first-line treatment. 2, 1
• Cholestyramine is effective but may be unpalatable; colesevelam is better tolerated but more expensive. 2
• Loperamide can also be used as adjunctive therapy. 2

For Small Intestinal Bacterial Overgrowth

• Empirical treatment with broad-spectrum antibiotics such as rifaximin is recommended when diagnosis is likely, with recurrent courses as needed. 1
• Treatment should be considered even without definitive breath testing if clinical presentation is consistent with SIBO. 2

Common Pitfall to Avoid

• Do not assume that persistent diarrhea and odor changes after bowel resection represent disease recurrence (in Crohn's patients) or surgical failure without first ruling out bile acid malabsorption, SIBO, and functional causes, as these non-inflammatory conditions are far more common and highly treatable. 2, 1