Schatzkin 2000.

Methods	Allocation: randomised Blindness: no Duration: 4 years (with a further follow‐up after an additional 4 years) Setting: 8 clinical centres, USA
Participants	Inclusion criteria: ≥ 1 large bowel adenoma removed within 6 months, polyp‐free colon post colonoscopy, age ≥ 35 years Exclusion criteria: CRC, bowel resection, IBD, FAP, weight > 150% of recommended, lipid‐lowering drugs N = 2079 Sex: % male (intervention/control) 65.8/63.2 Age: mean (intervention/control) 61.0/61.1 Baseline dietary fibre intake g/d: not reported Baseline characteristics similar for each group: yes
Interventions	Treatment: dietary targets of 20% of calories from fat, 18 g of dietary fibre/1000 kcal, and 5‐8 servings of fruits and vegetables/d. Over 50 h of dietary counselling. N = 1037 Control: general dietary guidelines with no additional information provided. N = 1042
Outcomes	Adenoma recurrence Colorectal cancer occurrence Adenoma size Multiple adenomas
Notes	Colonoscopy +/‐ polypectomy at 1 and 4 years after randomisation. Adenoma defined as recurrent if it was found during any endoscopic procedure after the 1‐year colonoscopy Treatment group reduced fat intake to approximately 25% of calories, doubled fibre intake to 30‐35 g/d Adverse effects not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomisation stratified by clinical centre. Assignment done by a computer programme
Allocation concealment (selection bias)	Unclear risk	No details
Blinding (performance bias and detection bias) All outcomes	High risk	Participants were aware of treatment regimens.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Participants were aware of allocation, but were told not to tell the endoscopist.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Reasons for loss to follow‐up were reported, 174 out of 2079 participants (8.4%) dropped out from the study.
Selective reporting (reporting bias)	Low risk	All measured outcomes were reported.
Other bias	Unclear risk	None identified

BC: beta carotene
 CRC: colorectal cancer
 IBD: inflammatory bowel disease
 FAP: familial adenomatous polyposis
 ITT: intention‐to‐treat
 RCT: randomised controlled trial
 WBF: wheat bran fibre