The hypothesis that a diet rich in fibre reduces affection with colorectal cancer risk could be confirmed in the study. The results indicate that fibre acts protectively against the development of polyps as well as against their malignant transformation. It is assumed that in populations with low intake of dietary fibre, a doubling of intake from foods could reduce the risk of affection with colorectal cancer by as much as 40%.
The consumption of red meat increases colorectal cancer risk whereas fish decreases the risk. A high intake of meat also appears to be associated with gastric cancer. Diet diversity, however, was found to be negatively correlated with gastric cancer. Fruit can considerably reduce the risk for lung cancer, an EPIC study found a reduction by 40% between the quintiles with the highest and the lowest fruit intake (results adjusted for tobacco smoking).
By contrast, breast and prostate cancer risks are not correlated with the consumption of fruit and legumes. According to preliminary results, current alcohol intake is significantly positively associated with the risk of affection with rectal, but not colon cancer.

Finally, a glance at energy intake: Numerous laboratory trials on mice, rats, worms, flies and yeast in the past have demonstrated that low energy intake increased lifespan and had a protective effect against cancer. A gene called SIR2 is supposed to control this process. Not surprisingly, EPIC studies confirm that obesity is associated with increased risk of a number of cancers, including breast, pancreatic and colorectal cancer, as well as renal cell carcinoma.

Diet, Autophagy, and Cancer: a review
Dietary factors can modulate processes of carcinogenesis. Based on this knowledge, strategies for cancer prevention and therapy can be found. Dietary factors can modulate cancer risk by suppressing cancer or by stimulating programmed cell death. Type I apoptotic pathway is well characterized, but not the only pathway. Also macroautophagy-related pathway (type II) and necrosis (type III) or combinations thereof are possible. The induction of macroautophagy may contribute to either the survival or death of cells in response to a stressor. Keith Singletary analyzes the interactions among bioactive food, autophagy and cancer. Food components like vitamin D, selenium, resveratrol and genistein stimulate autophagy vacuolization. Hence, it is difficult to determine if this is a protumorigenic or antitumorigenic response.

Dietary polyphenols may affect DNA methylation
Certain dietary polyphenols, such as EGCG from green tea and genistein from soybean, inhibit DNA methyltransferases (DNMT) in vitro. This inhibitory activity is associated with the demethylation of CpG island in promoters and the reactivation of methylation-silenced genes such as p16. These activities have been observed in various human cancer cell lines. The activity can be enhanced by the presence of histone deacetylase inhibitor or by a longer-term treatment. Catechol polyphenols may indirectly inhibit DNMT. Prevention or reversal of hypermethylation-induced inactivation of key tumor suppressor genes by DNMT inhibitors could be used for cancer prevention. Due to a rather low bioavailability of most polyphenolic compounds, to what extend for humans is still unclear. The effect of normal dietary consumption is probably insignificant, a combination or additive effect may affect DNA methylation status.

References
Miller AB et al.Dietary fibre in food and protection against colorectal cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC): an observational study. Lancet. 2003 May 3;361(9368):1496-501

Pischon T et al. Fruits and vegetables and lung cancer: Findings from the European Prospective Investigation into Cancer and Nutrition. Int. J. Cancer 2004;108: 269-276.

Body size and risk of colon and rectal cancer in the European Prospective Investigation Into Cancer and Nutrition (EPIC).; J Natl. Cancer Inst. Jul 5; 98(13):920-31

Singletary K and Milner J. Diet, autophagy, and cancer: a review. Cancer Epidemiol Biomarkers Prev. 2008 Jul;17(7):1596-610.

Fang M et al. Dietary polyphenols may affect DNA methylation. J Nutr. 2007 Jan;137(1 Suppl):223S-228S.