Understanding Chronic Loose Stools After Right-Sided Colon Cancer Surgery: What a New Danish Study Reveals

Table of Contents

• Key Points
• Why This Research Matters
• How the Study Was Conducted
• Key Findings: What the Researchers Discovered
• Treatment Results: Symptoms Improved With Targeted Therapy
• What This Means for Patients
• Study Limitations
• Recommendations for Patients
• Frequently Asked Questions
• Source Information

Key Points

• In a Danish study of 64 patients, 82% of those with chronic loose stools after right-sided hemicolectomy had bile acid malabsorption (BAM), versus 37% without loose stools.
• SIBO was common (73% of cases, 74% of controls) but not linked to loose stools; antibiotics often failed to clear it, with 73% still positive on retest.
• Treatment with bile acid sequestrants (cholestyramine or colesevelam) and/or antibiotics significantly improved stool consistency, frequency, urgency, and incontinence.
• Gut transit time was normal in both groups, suggesting loose stools are not caused by fast transit but by how bile acids are handled.
• The study was small (45 cases, 19 controls), and SeHCAT scanning is not available in all countries, which may limit generalisability.

Why This Research Matters

The number of colorectal cancer survivors has risen dramatically over the past decades. While much attention has been paid to bowel problems after rectal cancer surgery, far less research has focused on bowel function after colon cancer surgery. This is a significant gap, because the available evidence shows that patients who have undergone right-sided hemicolectomy frequently report bothersome symptoms.

Recent studies have shown that patients who undergo a right-sided hemicolectomy—a surgery that removes the right portion of the colon, a small segment of the end of the small intestine (terminal ileum), and the ileocaecal valve—often experience frequent bowel movements, loose or liquid stools, faecal urgency, faecal incontinence, and the need to defecate at night. In contrast, patients who have sigmoid resection (surgery on the left side of the colon) mainly suffer from straining and a feeling of incomplete evacuation.

Loose stools, defined as type 6 (fluffy or mushy) or type 7 (liquid) on the Bristol Stool Chart, are significantly more common among right-sided hemicolectomy patients than in the general population. What has been unclear, however, is why this happens. Understanding the root cause is essential because it determines what treatment will actually help.

Two possible culprits have been identified:

• Bile acid malabsorption (BAM) — a condition in which the gut fails to properly reabsorb bile acids produced by the liver, leading to excess bile acids in the colon, which triggers watery stools.
• Small intestinal bacterial overgrowth (SIBO) — an overgrowth of bacteria in the small intestine, which can damage the intestinal lining and interfere with nutrient absorption, potentially causing loose stools.

BAM can be classified into three types. Type 1 is caused by ileal dysfunction due to resection or inflammation (true malabsorption). Type 2 is primary or idiopathic (no known cause). Type 3 is secondary to other disorders such as coeliac disease, pancreatic dysfunction, gallbladder removal (cholecystectomy), or SIBO. In types 2 and 3, the problem is an excessive amount of bile acids in the bowel.

During a right-sided hemicolectomy, the terminal ileum is resected, and the ileocaecal valve is removed. The terminal ileum is the main site where bile acids are reabsorbed, and the ileocaecal valve normally prevents colonic bacteria from migrating backwards into the small intestine. This makes it biologically plausible that right-sided hemicolectomy could lead to both BAM and SIBO. However, until this study, no research had systematically investigated how often these conditions occur in this patient population.

How the Study Was Conducted

The research team, based at Aarhus University Hospital and Aalborg University Hospital in Denmark, conducted a case–control study between September 2017 and November 2020. They enrolled patients with a primary adenocarcinoma in the right side of the colon who had been treated with curatively intended right-sided or extended right-sided hemicolectomy. All patients had undergone surgery at least 1 year before inclusion.

Forty-five patients with chronic loose stools (cases) were compared with 19 patients without loose stools (controls) who had undergone the same type of surgery. The controls had normal bowel function, defined as Bristol stool type 3–4. Cases were recruited from a previous questionnaire study and through the Danish Cancer Society Centre for Research on Survivorship and Late Adverse Effects after Cancer. Control patients were matched to cases based on gender and age.

Patients were excluded if they had undergone other major gastrointestinal, urological, or gynaecological surgery (to avoid bowel dysfunction from pelvic surgery), or if they had radiation therapy, colon cancer recurrence, a permanent stoma, or were pregnant.

Each patient underwent a systematic set of diagnostic tests:

1. Blood tests and stool samples — to screen for common causes of chronic loose stools, including lactose intolerance, coeliac disease, inflammatory bowel disease, thyroid disorders, and pancreatic exocrine deficiency.
2. SeHCAT scan — a nuclear medicine test that measures the 7-day retention of a synthetic, radiolabelled bile acid. Retention below 15% was considered diagnostic for BAM; 15–20% was defined as borderline. Severity was graded as severe (retention <5%), moderate (5% to <10%), or mild (10% to <15%).
3. Hydrogen and methane breath tests — to diagnose SIBO. An increase of at least 10 parts per million (ppm) of hydrogen or methane was considered diagnostic.
4. Gastrointestinal transit time (GITT) — measured using the Gothenburg radiopaque marker method, to assess how quickly food moves through the digestive tract.
5. FGF19 measurement — in a subgroup (21 cases and 9 controls), fasting blood levels of fibroblast growth factor 19 (FGF19), a hormone produced in the terminal ileum that regulates bile acid production in the liver, were measured using an ELISA test.

Treatment followed a published algorithm. Patients with SIBO and matching symptoms (loose stools, bloating) received antibiotics for 6–7 days: ciprofloxacin was first choice, followed by rifaximin if symptom relief was insufficient. Breath tests were repeated after antibiotic treatment. Patients with BAM were treated with bile acid sequestrants: cholestyramine was first choice (with gradual dose titration), and colesevelam was prescribed if cholestyramine was intolerable or ineffective. A fat-reduced diet guided by a specialised dietician was offered as a supplement if needed.

The study was approved by the Committee on Health Research Ethics in the Central Denmark Region, registered in the Central Denmark Region's register of research projects, and listed on ClinicalTrials.gov (NCT number: NCT04003181). It was written according to the STROBE recommendations for observational studies.

Key Findings: What the Researchers Discovered

Patient characteristics

The two groups were largely similar in age, gender, and type of surgery. Cases had a median age of 71 years (range 35–88), and controls had a median age of 72 years (range 61–86). Fifty-six percent of cases were female, compared to 47% of controls.

Time since surgery was comparable between the groups (median 3.8 years for cases vs. 5.9 years for controls, p = 0.292). The majority of patients in both groups had a standard right-sided hemicolectomy (87% of cases, 84% of controls), with the remainder having an extended right-sided hemicolectomy. Adjuvant chemotherapy (fluorouracil-based treatment) had been given to 43% of cases and 42% of controls.

Among the 45 cases with chronic loose stools, the symptom burden was severe:

• 98% (41 patients) suffered from faecal urgency
• 62% (26 patients) experienced incontinence for liquid stool
• 44% (19 patients) had 4 or more bowel movements per day

Bile acid malabsorption (BAM) was strongly linked to loose stools

The most striking finding was that BAM was present in 82% (36 of 45) of patients with chronic loose stools, compared with only 37% (7 of 19) of controls — a difference that was statistically highly significant (p < 0.001). This means there is less than a 0.1% chance that this difference occurred randomly.

The odds of having BAM were 7.71 times higher in patients with loose stools than in those without (95% confidence interval: 2.31–25.78). In other words, patients with chronic loose stools after right-sided hemicolectomy were nearly 8 times more likely to have BAM.

The majority of cases had severe BAM (retention below 5%), with 20 of 45 patients falling into this category. Surprisingly, the majority of controls diagnosed with BAM also had severe BAM — meaning some patients can have significant bile acid malabsorption without experiencing loose stools.

SIBO was common but not linked to loose stools

SIBO was diagnosed in 73% (33 of 45) of cases and 74% (14 of 19) of controls — virtually identical rates (p = 0.977). This finding suggests that bacterial overgrowth in the small intestine is a frequent consequence of right-sided hemicolectomy (likely due to removal of the ileocaecal valve), but it does not appear to be the primary driver of chronic loose stools in this patient group.

No association was observed between BAM and SIBO. The researchers specifically tested whether the two conditions overlapped, but the data showed they occur independently.

Gut transit time was normal

Gastrointestinal transit time was similar in both groups: a median of 1.0 days in cases and 1.2 days in controls (p = 0.127). This finding is important because it shows that loose stools in these patients are not caused by food moving through the gut too quickly. The problem lies in how bile acids are handled, not in transit speed.

FGF19 did not predict BAM in this population

In the subgroup tested (21 cases and 9 controls), median FGF19 levels were nearly identical: 90.7 pg/ml (IQR 67.9–135.8) in cases vs. 93.9 pg/ml (IQR 78.1–115.0) in controls (p = 0.894). There was also no correlation between FGF19 and SeHCAT retention (Spearman's r = 0.20, p = 0.294). This is an unexpected result, since previous research in other patient groups has shown that low SeHCAT retention correlates well with low FGF19. The authors note that FGF19 levels fluctuate throughout the day in response to meals, while SeHCAT retention reflects a 7-day period, which may help explain the discrepancy. They suggest that FGF19 measurement may not be useful in this specific patient group.

Screening for other causes

Routine screening ruled out several other potential causes of loose stools:

• Two cases and three controls had a genetic predisposition to lactose intolerance
• Three cases had faecal elastase below 100 μg/g (suggesting possible pancreatic enzyme insufficiency)
• Four cases had faecal calprotectin above 200 mg/kg (a marker of intestinal inflammation), despite a normal colonoscopy
• No participants were diagnosed with coeliac disease
• Haemoglobin, ferritin, and folate levels were normal in all participants

These patients remained in the study because they had been asymptomatic before their cancer treatment.

Treatment Results: Symptoms Improved With Targeted Therapy

Following the treatment algorithm, all 33 patients with chronic loose stools who had SIBO received antibiotics (ciprofloxacin or rifaximin). Of these, 26 had a second breath test after treatment. The breath test remained positive in 19 of 26 patients (73%), suggesting that antibiotic treatment often fails to permanently eradicate SIBO in this population.

Six patients who had both BAM and SIBO experienced sufficient symptom relief after antibiotic treatment alone that no further therapy was needed. Of these, five still had a positive breath test. In three of these patients, a repeat SeHCAT scan was performed after their bowel function normalised: retention remained severely low in two and showed borderline BAM in one.

Eight cases (18%) had normal SeHCAT retention, meaning they did not have BAM. Six of these patients were treated with antibiotics for SIBO. After treatment, three still had bowel dysfunction and a positive breath test; two received repeated rounds of antibiotics and one received dietary intervention.

Twenty-six patients diagnosed with BAM were treated with the bile acid sequestrant cholestyramine. Twelve of these also required colesevelam due to insufficient effect or discomfort from cholestyramine.

Bowel symptoms improved significantly across the board after treatment with antibiotics, bile acid sequestrants, and/or dietary intervention. The table below summarises the key improvements (all with p < 0.001):

• Stool consistency: Before treatment, 100% of cases had Bristol type 6 (61.9%) or type 7 (38.1%) stools. After treatment, type 6 dropped to 20.9% and type 7 to 0%, with 77% achieving type 2–5.
• Bowel movement frequency: Before treatment, 44.2% had 4 or more bowel movements per day; after treatment, only 11.6% did. The proportion with 1–3 bowel movements per day rose from 51.2% to 81.4%.
• Faecal urgency: The proportion experiencing urgency at least once per week dropped from 85.7% to 44.2%. The proportion who never had urgency rose from 2.4% to 16.3%.
• Incontinence for liquid stool: The proportion with daily incontinence fell from 9.5% to 0%, weekly incontinence from 23.8% to 7.0%, and the proportion who never experienced leakage rose from 38.1% to 67.4%.
• Pad use: Daily pad use declined from 29.3% to 18.6% (though this change did not reach statistical significance, p = 0.125).

What This Means for Patients

This study provides the most detailed picture to date of why chronic loose stools occur after right-sided hemicolectomy for colon cancer. The key message is clear: BAM is a major, treatable cause of chronic loose stools in this patient population.

For patients suffering from loose stools, urgency, and incontinence after right-sided colon surgery, these findings are genuinely encouraging. Instead of being told that bowel problems are just an unavoidable consequence of surgery, patients can now undergo targeted diagnostic testing—particularly a SeHCAT scan — to determine whether BAM is the culprit. If BAM is confirmed, treatment with bile acid sequestrants such as cholestyramine or colesevelam can substantially improve stool consistency, reduce bowel movement frequency, and decrease urgency and incontinence.

The study also clarifies the role of SIBO. Although bacterial overgrowth is extremely common after right-sided hemicolectomy (affecting nearly three-quarters of all patients), it does not appear to be the main cause of loose stools. This is an important distinction, because it suggests that treating SIBO alone with antibiotics may not resolve bowel symptoms for most patients, and that attention should focus primarily on diagnosing and treating BAM.

There is a strong scientific rationale for why BAM develops in these patients. During right-sided hemicolectomy, a 10 cm segment of the terminal ileum is removed along with the ileocaecal valve. The terminal ileum is responsible for reabsorbing bile acids, so removing part of it reduces the gut's resorptive capacity — consistent with type 1 BAM. The fact that 37% of controls also had BAM without loose stools suggests that bile acid diarrhoea is not simply a problem of transit, and that excess bile acids may affect individuals differently. This calls for further research into how bile acids affect colonic physiology.

Study Limitations

While this study offers important insights, several limitations should be acknowledged:

• Modest sample size: The study included 45 cases and 19 controls. While this was sufficient to detect the large difference in BAM prevalence, it limited the statistical power for other comparisons. The authors aimed to include 50 cases and 20 controls to narrow confidence intervals.
• Small FGF19 subgroup: FGF19 was measured in only 21 cases and 9 controls, making it difficult to draw firm conclusions about its usefulness in this patient group. The authors note that larger studies are needed.
• Possible selection bias: A significant proportion of cases (44%) were referred to a specialised cancer survivorship centre, which may mean they had more severe symptoms than the average patient.
• No universally available diagnostic test: SeHCAT scanning is not available in all countries, which may limit the generalisability of the diagnostic approach used here.
• FGF19 variability: The measurement of FGF19 in fasting blood may not accurately reflect the dynamic regulation of bile acid production, which changes in response to meals throughout the day.
• Long-term treatment adherence: The study shows that symptoms improve after treatment, but it does not address whether patients remain on bile acid sequestrants long-term. Previous research has shown that some patients abandon BAM treatment after a few years.

Recommendations for Patients

For colon cancer survivors who have undergone right-sided hemicolectomy and are living with chronic loose stools, urgency, or faecal incontinence, the following steps may be helpful:

1. Talk to your doctor about your symptoms. Loose stools, urgency, and incontinence are not just something you have to "live with" after cancer surgery. Effective treatments exist.
2. Ask about a SeHCAT scan. This nuclear medicine test is the most reliable way to diagnose BAM. It involves swallowing a small amount of radiolabelled synthetic bile acid and measuring how much is retained after 7 days. If retention is below 15%, BAM is confirmed.
3. Discuss bile acid sequestrants with your healthcare team. Cholestyramine is usually the first-choice medication. It needs to be gradually adjusted (titrated) to find the dose that works best with minimal side effects. Colesevelam is an alternative if cholestyramine is not well tolerated.
4. Be aware that antibiotics may not be the answer for loose stools. While SIBO is common after right-sided hemicolectomy, this study suggests it is not the main cause of chronic loose stools. If you are offered antibiotics for SIBO, keep in mind that the breath test often remains positive after treatment, and additional treatment for BAM may still be needed.
5. Consider dietary support. A permanent fat-reduced diet, guided by a specialised dietician, may be a useful supplement to medication. Reducing fat intake can reduce the amount of bile acids delivered to the colon.
6. Seek care at a specialised centre. Hospitals with expertise in cancer survivorship, gastroenterology, and nuclear medicine are best equipped to perform the full diagnostic workup and tailor treatment to your specific needs.
7. Ask about other causes. The study also screened for lactose intolerance, coeliac disease, thyroid disorders, pancreatic insufficiency, and inflammatory bowel disease. If you have persistent symptoms, ensure these have been ruled out as well.

The study's findings suggest that a firm diagnosis based on SeHCAT before starting treatment is important. If you are considering treatment for BAM, ask your doctor whether a SeHCAT scan is available and appropriate for you. Because BAM can be a lifelong condition, a clear diagnosis helps guide long-term management.

Frequently Asked Questions

What causes chronic loose stools after right-sided colon cancer surgery?

In a Danish study of 64 patients, bile acid malabsorption (BAM) was found in 82% of those with chronic loose stools after right-sided hemicolectomy, compared with 37% without loose stools. BAM occurs when the gut cannot reabsorb bile acids, leading to watery stools. Small intestinal bacterial overgrowth was common but not linked to loose stools.

How is bile acid malabsorption diagnosed after right-sided hemicolectomy?

The SeHCAT scan is used to diagnose BAM. It measures how much radiolabelled bile acid is retained after 7 days. Retention below 15% confirms BAM; 15–20% is borderline. In the Danish study, this scan identified BAM in 82% of patients with chronic loose stools after right-sided hemicolectomy. Ask your doctor if this test is available.

What treatments improved bowel symptoms in the Danish study?

Patients with BAM received bile acid sequestrants: cholestyramine first, or colesevelam if needed. Those with SIBO received antibiotics (ciprofloxacin or rifaximin). After treatment, stool consistency improved, with 77% achieving Bristol type 2–5, and daily incontinence fell from 9.5% to 0%. A fat-reduced diet guided by a dietician was offered as a supplement.

Does small intestinal bacterial overgrowth (SIBO) cause loose stools after right-sided hemicolectomy?

In the Danish study, SIBO was found in 73% of patients with loose stools and 74% without, so it was not linked to loose stools. Antibiotics for SIBO often failed to clear it: after treatment, 73% of retested patients still had a positive breath test. This suggests SIBO is common after surgery but not the main driver of loose stools.

What does a SeHCAT retention result below 15% mean?

A SeHCAT retention below 15% means bile acid malabsorption (BAM) is confirmed. In the Danish study, most patients with chronic loose stools had severe BAM (retention below 5%). However, 37% of patients without loose stools also had BAM, often severe, so the result must be interpreted with your symptoms and medical history.

Are antibiotics effective for loose stools after right-sided hemicolectomy?

In the Danish study, antibiotics for SIBO did not permanently eradicate it: 73% of retested patients still had a positive breath test. However, six patients with both BAM and SIBO had sufficient symptom relief after antibiotics alone. For most, treating BAM with bile acid sequestrants was needed to improve loose stools, urgency, and incontinence.

What should I do if I have loose stools, urgency, or leakage after right-sided colon surgery?

Talk to your doctor about your symptoms. Ask about a SeHCAT scan to check for bile acid malabsorption. If confirmed, bile acid sequestrants such as cholestyramine or colesevelam can improve stool consistency, frequency, urgency, and incontinence. A fat-reduced diet guided by a dietician may help. Seek care at a centre experienced in cancer survivorship and gastroenterology.

I had right-sided colon cancer surgery and still have chronic loose stools, urgency and leakage — when should I seek a second opinion?

When loose stools, urgency or leakage persist after right-sided hemicolectomy, a second opinion is reasonable before accepting these symptoms as permanent. Bile acid malabsorption is present in 82% of patients with chronic loose stools after this surgery, and a SeHCAT scan showing retention below 15% confirms it. Bile acid sequestrants such as cholestyramine or colesevelam substantially improve stool consistency, frequency, urgency and leakage. SIBO is common but not the main driver, so antibiotics alone often leave symptoms unresolved. Diagnostic Detectives Network provides independent expert second opinions.

Source Information

Original Article: "Chronic loose stools following right-sided hemicolectomy for colon cancer and the association with bile acid malabsorption and small intestinal bacterial overgrowth"

Authors: Helene Mathilde Larsen, Klaus Krogh, Mette Borre, Tine Gregersen, Mette Mejlby Hansen, Anne K. Arveschoug, Peter Christensen, Asbjørn Mohr Drewes, Katrine Jøssing Emmertsen, Søren Laurberg, and Janne Ladefoged Fassov

Affiliation: Danish Cancer Society Centre for Research on Survivorship and Late Adverse Effects after Cancer in the Pelvic Organs, Aarhus and Aalborg, Denmark; Departments of Surgery, Hepatology and Gastroenterology, Nuclear Medicine & PET, and Regional Hospital Randers

Publication: Colorectal Disease, 2023; Volume 25, pages 600–607 (DOI: 10.1111/codi.16409). Received 22 April 2022; revised 8 September 2022; accepted 1 October 2022.

Funding: GE Healthcare; Danish Cancer Society

Registration: ClinicalTrials.gov (NCT number: NCT04003181)

Note: This patient-friendly article is based on peer-reviewed research. It is intended for educational purposes and is not a substitute for professional medical advice. Patients should always consult their healthcare provider regarding their specific medical condition and treatment options.