What is the role of diet in cancer prevention?
This is a controversial area with conflicting data in the literature. Dietary modifications are difficult to promote in populations.
Dietary fat and cancer
Dietary fat promotes tumour growth in animal models, and conversely energy restriction appears to reduce the incidence of tumours.
Excess dietary fat is associated with cancer of the breast, colon, endometrium, and prostate. Dietary studies are fraught with methodological problems, but nonetheless there are increasing case control and cohort studies to point towards an association of excess fat in the diet with breast and colon cancer, in particular. The data showing the relationship between a high-fat diet and prostate cancer are conflicting.
Dietary fibre and cancer
Diets with increased fibre tend to reduce colonic transit time and bind some potentially carcinogenic chemicals.
RCTs of dietary manipulation are extremely difficult and are dogged by poor compliance.
In over a dozen case studies, a meta-analysis indicates an inverse relationship between fibre intake and colon cancer. These are mostly retrospective studies. Prospective studies have produced conflicting data, in particular, the huge Nurses’ Health Study.
- There is no evidence that increasing fibre in the diet inhibits the development of colorectal adenomas.
- Evidence that increased fibre in the diet inhibits the development of colorectal cancer is uncertain, and data are conflicting.
- Similarly, whilst high-fibre diets may reduce the risk of breast and stomach cancers, the data are unclear.
Fruit and vegetable consumption
Again, data are conflicting, and the Nurses’ Health Study revealed no association between the consumption of fruit and vegetables 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, but again data are conflicting.
- There appears to be little association between fruit and vegetable consumption and 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 and 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.
Carotenoids and cancer
These are antioxidants and promote cell differentiation. β-carotene has been investigated, and the data are conflicting.
In some cancers, early data are encouraging (aspirin in colorectal cancer prevention), whereas, in lung cancer, vitamin supplementation has no proven role.