This has previously been a controversial area of research, as some recent studies have suggested no association between increased fibre intake and a reduced risk of colorectal cancer.
Ulrike Peters from the National Cancer Institute, Rockville, USA, and colleagues assessed the relation of fibre intake and frequency of colorectal adenoma (non-malignant polyps which are often a precursor of malignant disease). The study was done within the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, a randomised controlled trial designed to investigate methods for early detection of cancer. The investigators compared fibre intake of around 34,000 participants who did not have polyps, with around 3600 people with at least one adenoma in the distal large bowel (ie, descending colon, sigmoid colon, or rectum).
High intake of dietary fibre was associated with a lower risk of colorectal adenoma-after adjustment for potential dietary and non-dietary risk factors. Participants in the top 20% for dietary fibre intake had around a quarter lower risk of adenoma compared to people in the bottom 20% for fibre intake (representing an increase in fibre intake of 24 grammes per day). This association was strongest for fibre from grains, cereals, and fruits, although there was no association between fibre intake and risk of rectal cancer.
A European study also published in this week's issue (p 1496) reports similar findings. Sheila Bingham and Nick Day from the UK Medical Research Council, Elio Riboli from the WHO International Agency for Research on Cancer, and colleagues from the European Prospective Investigation into Cancer (EPIC) consortium prospectively examined the association between dietary fibre intake and incidence of colorectal cancer in over half a million individuals aged 25-70 years, recruited from ten European countries.
After an average follow-up of 4.5 years, 1065 cases of colorectal cancer were diagnosed. Individuals from the top 20% for fibre intake, who ate 35 g fibre per day on average, had their risk of colorectal cancer reduced by a quarter compared with individuals consuming 15 g per day on average. This reduction in risk was estimated to be 40% after a more sensitive analysis was done. The protection was strongest for left-sided colon cancer and not significant for rectal cancer.
In an accompanying Commentary (p 1487) Lynnette Ferguson and Philip Harris from the University of Auckland, New Zealand, state how the new results 'give fresh impetus to fundamental research to determine the reasons for the protective action of dietary fibre'. They conclude: "Whatever the reasons for the results reported by the two studies, eating a diet rich in plant foods, in the form of fruit, vegetables, and whole-grain cereals, probably remains the best option for reducing the risk of colon cancer, and for more general health protection."
Contact: Dr Ulrike Peters, Nutritional Epidemiology Branch, Division of Cancer Epidemiology & Genetics, National Cancer Institute, 6120 Executive Boulevard EPS#3024, Rockville, MD 20892-7273, USA;
T) (NCI Press Office) 301-496-6641 or 301-594-7097;
F) 301-496-6829;
E) petersu@mail.nih.gov
Dr Sheila A Bingham, MRC Dunn Human Nutrition Unit, Wellcome Trust / MRC Building, Hills Road, Cambridge, CB2 2XY, UK;
T) +44 (0)1223 252760;
F) 44-122-325-2765;
E) sab@mrc-dunn.cam.ac.uk
Dr Lynnette Ferguson, Discipline of Nutrition, University of Auckland, Auckland, New Zealand;
T) 64-9-373-7599 ext 6372;
F) 64-9-373-7502;
E) l.ferguson@auckland.ac.nz
Journal
The Lancet