Oxford American handbook of oncology. Second Edition. Oxford University Press (2015)
This is a controversial area with conflicting data in the literature. Dietary modifications are difficult to promote in populations and compliance is often poor.
Dietary fat promotes tumor growth in animal models and, conversely, energy restriction appears to reduce the incidence of tumors. Excess dietary fat is associated with cancer of the breast, colon, endometrium, and prostate.
Dietary studies are fraught with methodological problems:
- There are increasing case-control and cohort studies pointing towards an association of excess fat in the diet with breast and colon cancer in particular.
- However, conflicting data on these associations continue to appear.
Data on the relationship between a high-fat diet and prostate cancer are also conflicting.
Diets with increased fiber tend to reduce colonic transit time and bind some potentially carcinogenic chemicals. Randomized control trials of dietary manipulation are extremely difficult and are dogged by poor compliance.
Data from over a dozen case-control studies and a meta-analysis indicate an inverse relationship between fiber intake and colon cancer.
However, prospective studies have yielded conflicting data, in particular the large Nurses’ Health Study.
There is no evidence that increasing fiber in the diet inhibits the development of colorectal adenomas. Evidence that increased fiber in the diet inhibits the development of colorectal cancer is still uncertain, and data are conflicting. Similarly, although high-fiber diets may reduce the risk of breast cancer and stomach cancer, studies have revealed conflicting data.
Fruit and vegetable consumption
Data from the Nurses’ Health Study have shown no association between the consumption of fruit and vegetables and subsequent cancer risk during over 1.5 million person-years of follow-up.
Some studies have found an inverse association between fruit and vegetable consumption and stomach cancer, although the data are conflicting.
There appears to be little association between fruit and vegetable consumption and the risk of breast cancer.
High consumption of fruit and vegetables may be protective for men and women who have never smoked in the development of lung cancer.
Folate may reduce carcinogenesis through DNA repair and DNA methylation. In animals, folate deficiency increases intestinal carcinogenesis.
A diet rich in folate may lower the risk of colorectal cancer and the precursor adenoma. Several studies have shown that folate supplementation can decrease colorectal cancer risk.
These are antioxidants and promote cell differentiation. β-carotene has been investigated and the data are conflicting. In smokers, β-carotene caused an increased risk of lung cancer in two large randomized studies and in other smaller studies.