Abstract
Observational studies report that higher intake of dietary fibre (a heterogeneous mix including non-starch polysaccharides and resistant starches) is associated with reduced risk of colorectal cancer, but no randomised trials with prevention of colorectal cancer as a primary endpoint have been done. We assessed the effect of resistant starch on the incidence of colorectal cancer. In the CAPP2 study, individuals with Lynch syndrome were randomly assigned in a two-by-two factorial design to receive 600 mg aspirin or aspirin placebo or 30 g resistant starch or starch placebo, for up to 4 years. Randomisation was done with a block size of 16. Post-intervention, patients entered into double-blind follow-up; participants and investigators were masked to treatment allocation. The primary endpoint for this analysis was development of colorectal cancer in participants randomly assigned to resistant starch or resistant-starch placebo with both intention-to-treat and per-protocol analyses. This study is registered, ISRCTN 59521990. 463 patients were randomly assigned to receive resistant starch and 455 to receive resistant-starch placebo. At a median follow-up 52·7 months (IQR 28·9-78·4), 53 participants developed 61 primary colorectal cancers (27 of 463 participants randomly assigned to resistant starch, 26 of 455 participants assigned to resistant-starch placebo). Intention-to-treat analysis of time to first colorectal cancer showed a hazard ratio (HR) of 1·40 (95% CI 0·78-2·56; p=0·26) and Poisson regression accounting for multiple primary events gave an incidence rate ratio (IRR) of 1·15 (95% CI 0·66-2·00; p=0·61). For those completing 2 years of intervention, per-protocol analysis yielded a HR of 1·09 (0·55-2·19, p=0·80) and an IRR of 0·98 (0·51-1·88, p=0·95). No information on adverse events was gathered during post-intervention follow-up. Resistant starch had no detectable effect on cancer development in carriers of hereditary colorectal cancer. Dietary supplementation with resistant starch does not emulate the apparently protective effect of diets rich in dietary fibre against colorectal cancer. European Union, Cancer Research UK, Bayer Corporation, National Starch and Chemical Co, UK Medical Research Council, Newcastle Hospitals Trustees, Cancer Council of Victoria Australia, THRIPP South Africa, The Finnish Cancer Foundation, SIAK Switzerland, and Bayer Pharma.
Highlights
The incidence of colorectal cancer rises steeply with age and risk is affected strongly by environmental factors including adiposity, physical activity, and habitual diet.[1]
There was no evidence of any interaction between the effects of aspirin and starch (Mantel-Haenszel χ2 [1 degree of freedom] 0·02; p=0·9), for completeness, we report the effects of resistant starch adjusted for aspirin usage
An earlier pooled analysis of prospective cohort studies[25] showed no effect of dietary fibre on risk of colorectal cancer after adjusting for other dietary factors but that analysis included fewer studies and fewer cases of colorectal cancer and had a narrower geographical reach compared with the recent systematic review and meta-analysis by Aune and colleagues.[2]
Summary
The incidence of colorectal cancer rises steeply with age and risk is affected strongly by environmental factors including adiposity, physical activity, and habitual diet.[1]. The evidence was assessed as probable that alcoholic drinks (women only) increase risk whereas foods containing dietary fibre and garlic, milk, and calcium reduce risk of colorectal cancer.[1] A recent metaanalysis of 21 prospective studies showed a significant, dose-dependent protective effect of dietary fibre intake against colorectal cancer (relative risk [RR] per 10 g a day increase in dietary fibre intake 0·90, 95% CI 0·86–0·94).[2]. Observational studies report that higher intake of dietary fibre (a heterogeneous mix including nonstarch polysaccharides and resistant starches) is associated with reduced risk of colorectal cancer, but no randomised trials with prevention of colorectal cancer as a primary endpoint have been done. We assessed the effect of resistant starch on the incidence of colorectal cancer
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