Colon cancer risk: Supplements no substitute for dietary fiber

Dietary supplementation with resistant starch does not reduce long-term colorectal cancer risk in patients with Lynch syndrome, shows the CAPP2 study.

"Our study shows that supplementation with resistant starch does not emulate the apparently protective effect against colorectal cancer of diets rich in dietary fibre," say John Mathers (Newcastle University, UK) and colleagues.

In all, 918 patients with Lynch syndrome, who have a mutation predisposing them to colorectal cancer, were randomly assigned to receive 30 g resistant starch or starch placebo daily as part of CAPP2 (Colorectal Adenoma/carcinoma Prevention Programme).

Previously published results showed that, after an average treatment time of 29 months, there was no effect of resistant starch on the development of neoplasias. Colon surveillance was then continued over a further 10 years in 714 of the patients.

Overall, 27 patients given resistant starch and 26 patients given placebo developed primary colorectal cancers by the end of follow up. Of these, 45 were detected during long-term follow up.

Interestingly, the authors found that patients who took resistant starch for less than 2 years had a significant 2.38-fold increased risk for colorectal cancer compared with placebo, while those who took starch supplements for more than 2 years had comparable outcomes to placebo.

The authors say this may be a chance finding but it could also suggest an adverse effect of short-term supplementation.

Mathers and colleagues also found no significant effect of resistant starch consumption on the incidence of other Lynch syndrome associated cancers.

Resistant starch has been suggested to have an antineoplastic effect due to the production of butyrate during fermentation in the colon. However, the authors say that individual carbohydrates have different effects on the bowel and it is unlikely that the benefits of combined consumption can be emulated by a single type.

"From a public health perspective, eating more of a variety of food rich in dietary fibre including wholegrains, vegetables, fruits, and pulses is a preferable strategy for reducing cancer risk," they conclude in The Lancet Oncology.

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