Objective To investigate the association between intake of dietary fibre and whole grains and risk of colorectal cancer.Design Systematic review and meta-analysis of prospective observational studies.Data sources PubMed and several other databases up to December 2010 and the reference lists of studies included in the analysis as well as those listed in published meta-analyses. Study selectionProspective cohort and nested case-control studies of dietary fibre or whole grain intake and incidence of colorectal cancer.Results 25 prospective studies were included in the analysis. The summary relative risk of developing colorectal cancer for 10 g daily of total dietary fibre (16 studies) was 0.90 (95% confidence interval 0.86 to 0.94, I 2 =0%), for fruit fibre (n=9) was 0.93 (0.82 to 1.05, I 2 =23%), for vegetable fibre (n=9) was 0.98 (0.91 to 1.06, I 2 =0%), for legume fibre (n=4) was 0.62 (0.27 to 1.42, I 2 =58%), and for cereal fibre (n=8) was 0.90 (0.83 to 0.97, I 2 =0%). The summary relative risk for an increment of three servings daily of whole grains (n=6) was 0.83 (0.78 to 0.89, I 2 =18%).Conclusion A high intake of dietary fibre, in particular cereal fibre and whole grains, was associated with a reduced risk of colorectal cancer. Further studies should report more detailed results, including those for subtypes of fibre and be stratified by other risk factors to rule out residual confounding. Further assessment of the impact of measurement errors on the risk estimates is also warranted. IntroductionColorectal cancer is the third most common type of cancer, with 1.2 million new cases diagnosed in 2008 worldwide, accounting for about 9.7% of all cases of cancer.1 Evidence from ecological studies, migrant studies, and secular trend studies suggest that environmental risk factors are of major importance in the cause of colorectal cancer. [2][3][4] Dietary factors have been suspected as important, but only intakes of red and processed meat and alcohol are considered to be convincing dietary risk factors for colorectal cancer. 5 In the 1970s, Burkitt proposed the hypothesis that dietary fibre reduces the risk of colorectal cancer, based on the observation of low rates of such cancer among rural Africans who ate a diet with a high fibre content. 6 Several plausible mechanisms have been proposed to explain the hypothesis, including increased stool bulk and dilution of carcinogens in the colonic lumen, reduced transit time, and bacterial fermentation of fibre to short chain fatty acids.7 However, although many epidemiological studies have investigated the association between fibre intake and risk of colorectal cancer, the results have not been consistent and the possibility of residual confounding by folate intake remains a controversial issue. 8 Case-control studies have generally shown a protective association, 9 10 whereas the results from cohort studies have been mixed. 8 11-31 In addition, it is not clear whether only specific types or sources of fibre are associated with the risk. Although initial c...

BackgroundThe evidence that red and processed meat influences colorectal carcinogenesis was judged convincing in the 2007 World Cancer Research Fund/American Institute of Cancer Research report. Since then, ten prospective studies have published new results. Here we update the evidence from prospective studies and explore whether there is a non-linear association of red and processed meats with colorectal cancer risk.Methods and FindingsRelevant prospective studies were identified in PubMed until March 2011. For each study, relative risks and 95% confidence intervals (CI) were extracted and pooled with a random-effects model, weighting for the inverse of the variance, in highest versus lowest intake comparison, and dose-response meta-analyses. Red and processed meats intake was associated with increased colorectal cancer risk. The summary relative risk (RR) of colorectal cancer for the highest versus the lowest intake was 1.22 (95% CI  = 1.11−1.34) and the RR for every 100 g/day increase was 1.14 (95% CI  = 1.04−1.24). Non-linear dose-response meta-analyses revealed that colorectal cancer risk increases approximately linearly with increasing intake of red and processed meats up to approximately 140 g/day, where the curve approaches its plateau. The associations were similar for colon and rectal cancer risk. When analyzed separately, colorectal cancer risk was related to intake of fresh red meat (RR for 100 g/day increase  = 1.17, 95% CI  = 1.05−1.31) and processed meat (RR for 50 g/day increase  = 1.18, 95% CI  = 1.10−1.28). Similar results were observed for colon cancer, but for rectal cancer, no significant associations were observed.ConclusionsHigh intake of red and processed meat is associated with significant increased risk of colorectal, colon and rectal cancers. The overall evidence of prospective studies supports limiting red and processed meat consumption as one of the dietary recommendations for the prevention of colorectal cancer.

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High intakes of dairy products, milk, low-fat milk, cheese, and total, dietary, and dairy calcium, but not supplemental or nondairy calcium, may increase total prostate cancer risk. The diverging results for types of dairy products and sources of calcium suggest that other components of dairy rather than fat and calcium may increase prostate cancer risk. Any additional studies should report detailed results for subtypes of prostate cancer.