Can stool smell differ after bowel resection surgery?

Can Stool Smell Change After Bowel Resection Surgery?

Yes, stool odor can definitely change after bowel resection surgery, primarily due to bile acid malabsorption, small intestinal bacterial overgrowth, and fat malabsorption—all of which are common physiological consequences of bowel resection that alter the bacterial fermentation and chemical composition of stool.

Primary Mechanisms Causing Odor Changes

Bile Acid Malabsorption

• Bile acid malabsorption occurs in more than 80% of patients following ileal resection, which is one of the most common causes of altered bowel function after surgery 1.
• When bile acids are not reabsorbed in the terminal ileum, they reach the colon where bacteria metabolize them, producing volatile compounds that change stool odor 1.
• This occurs even with resections as short as 5 cm of terminal ileum 1.
• The unabsorbed bile acids also contribute to diarrhea and steatorrhea (fatty stools), which have characteristically different and often more offensive odors 1.

Small Intestinal Bacterial Overgrowth (SIBO)

• SIBO occurs in approximately 30% of patients after bowel resection, particularly when the ileocecal valve is removed 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 gases (hydrogen and methane) and metabolic byproducts that alter stool odor 1.
• SIBO is more common with blind loops, dysmotility, diverticula, or strictures 1.

Fat Malabsorption and Steatorrhea

• Fat malabsorption occurs when more than 60-100 cm of terminal ileum has been resected because hepatic synthesis cannot compensate for the loss of bile salt reabsorption 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 (fatty, greasy stools) has a distinctly different and often more offensive odor than normal stool 1.

Type of Resection Matters

Right Hemicolectomy/Ileocolic Resection

• These procedures carry the highest risk for odor changes because they involve removal of the terminal ileum and ileocecal valve 1.
• The loss of ileal absorptive capacity for bile acids and the protective barrier function of the ileocecal valve create ideal conditions for both bile acid malabsorption and SIBO 1.

Jejunostomy Patients

• Patients with jejunostomies experience rapid transit and altered bacterial fermentation due to loss of the ileal brake mechanism 1.
• The effluent composition differs significantly from normal stool, affecting odor 1.

Left-Sided Resections

• Left hemicolectomy typically causes fewer odor changes than right-sided resections because the terminal ileum and ileocecal valve remain intact 1.

Clinical Implications

When to Investigate Further

• If stool odor changes are accompanied by diarrhea, weight loss, bloating, or malnutrition, investigation for bile acid malabsorption and SIBO is warranted 1.
• Nocturnal diarrhea and steatorrhea are never normal after surgery and require systematic evaluation 1.
• Consider faecal calprotectin testing to distinguish inflammatory recurrence (in Crohn's disease patients) from non-inflammatory causes 1.

Treatment Approaches

• For bile acid malabsorption: therapeutic trial of bile acid sequestrants (cholestyramine or colesevelam) is recommended as first-line treatment 1.
• For SIBO: empirical treatment with broad-spectrum antibiotics such as rifaximin is recommended when diagnosis is likely, with recurrent courses as needed 1.
• Dietary modifications including fat reduction and lactose elimination can help reduce malodorous stool 2, 3.

Common Pitfall to Avoid

Do not assume all post-resection symptoms are due to disease recurrence or normal postoperative changes. Non-inflammatory causes including bile salt malabsorption, bacterial overgrowth, and functional disorders should be systematically considered, especially when symptoms persist beyond 3 months 1. These conditions are highly treatable once properly diagnosed, and empirical treatment trials are often more practical than extensive testing 1.