| Methods | Dietary Intervention for Patients Polypectomized for tumours of the colorectum (DIPP) RCT, parallel, 2 arms (n‐3 EPA + DHA + n‐3 ALA vs nil), 24 months Summary risk of bias: moderate or high |
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| Participants | Patients previously polypectomised for colorectal tumours N: 104 intervention, 101 control Level of risk for CVD: low Men: 73.1% intervention, 74.3% control Mean age in years (SD): 58.3 (9.5) intervention, 59.7 (8.9) control Age range: 35‐75 Smokers: 65.4% intervention, 61.4% control Hypertension: not reported Medications taken by at least 50% of those in the control group: supplements Medications taken by 20%‐49% of those in the control group: none Medications taken by some, but less than 20% of the control group: oral contraceptive pills Location: Japan Ethnicity: not reported |
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| Interventions | Type: advice + supplement (fish oil capsules) Comparison: EPA + DHA + ALA vs omega‐6 Intervention: advice to reduce total fat intake, decrease consumption of n‐6 PUFAs, increase intake of n‐3 PUFAs from fish/marine foods, increase intake of n‐3 PUFAs from perilla oil rich in ALA, take 8 capsules of fish oil/day (equivalent to 96 mg/day of EPA and 360 mg/day of DHA). Dose: 456mg/d EPA + DHA and unknown dose of ALA Control: advice to decrease intake of fats/oils as a whole Compliance: measured via semi‐quantitative food frequency questionnaire, plasma fatty acid concentrations, fatty acid compositions in the membranes of red blood cells and the sigmoid colon. Reported satisfactorily high compliance with protocol in both groups but no figures provided. Length of intervention: 24 months |
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| Outcomes | Main study outcome: number and size of colorectal tumours Dropouts: 3 intervention, 5 control Available outcomes: all cause mortality, dietary intake, plasma fatty acids, lipids, side effects, glucose Response to contact: yes (methodological details provided) |
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| Notes | Study funding: all were either government or charity grants | |
| Risk of bias | ||
| Bias | Authors' judgement | Support for judgement |
| Random sequence generation (selection bias) | Low risk | Randomly allocated using random digit number for allocation of participants |
| Allocation concealment (selection bias) | Low risk | Author confirmed "Allocation information was blinded to clinicians and researchers" |
| Blinding of participants and personnel (performance bias) All outcomes | Unclear risk | From the 2015 paper, "The attending physicians as well as the participants were blinded to the assignment information". However in the discussion section they say "complete participant blinding could not have been achieved because free living participants might have exchanged information on their dietary intervention, say in the hospital waiting room". Author confirmed blinding |
| Blinding of outcome assessment (detection bias) All outcomes | Low risk | Quote: "physicians, including colonoscopists, a scientist who conducted blood and specimen analyses, and pathologists were blinded" |
| Incomplete outcome data (attrition bias) All outcomes | Low risk | All those randomised were accounted for |
| Selective reporting (reporting bias) | High risk | The researchers chose not to report data on the number, size and pathological type of the colorectal tumours as they said they would in the trials register. They reported more outcomes in the paper than initially stated. UMIN000000461 Registered 3 August 2006, recruitment completed 1 March 2007 |
| Attention | Low risk | Participants were given equal follow‐up |
| Compliance | Unclear risk | Reported satisfactorily high compliance with protocol was noted in both groups but no figures |
| Other bias | Low risk | None noted |
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