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Non dietary risk factors for colorectal cancer:

  • Inheritance of mutations in APC or mismatch-repair genes
  • Ulcerative colitis
  • Schistosoma sinesis (especially important for rectal cancer in China)
  • Smoking

Non-dietary protective factors:

  • Physical activity
  • Aspirin and other NSAIDs

Dietary risk factors for cancer of the colon and rectum

CONVINCING EVIDENCE - decreases risk:

  • None

CONVINCING EVIDENCE - increases risk:

  • Red meat and processed meat
  • Alcoholic drinks (men)
  • Body fatness and abdominal fatness


PROBABLE EVIDENCE - decreases risk:

  • Foods containing fibre
  • Garlic
  • Milk
  • Calcium

PROBABLE EVIDENCE - increases risk:

  • Alcoholic drinks (women)


LIMITED/SUGGESTIVE EVIDENCE - decreases risk:
Vegetables and fruits
Foods containing folate, selenium and vitamin D
Fish

LIMITED/SUGGESTIVE EVIDENCE - increases risk:


Discussion questions:
Why is greater height possibly associated with higher risk of colorectal cancer?
What are the mechanisms by which garlic probably decreases risk? What about selenium and calcium?

Some possible dietary mechanisms - for cancer of the colon and rectum:

Heterocyclic amines may interact with important genes including APC and K-ras to cause somatic mutations (which occurs early in colorectal cancer)

Chronic folate and methionine deficiencies may produce alteration in DNA methylation, and therefore increase risk

High fat and high cholesterol diets may increase risk by increasing the amount of bile acids, and by increasing luminal free fatty acids

Dietary fibre could protect by
-binding bile acids
-increasing stool bulk (diluting carcinogens)
-lowering pH (through bacterial fermentation which reduces the conversion of primary to the more toxic secondary bile acids)
-producing short chain fatty acids which induce apoptosis

Calcium could protect by converting bile acids to insoluble calcium soaps, and by reducing cell proliferation by direct mechanisms

Vegetables may protect by providing fermentable fibre and anticarcinogenic compounds such as carotenoids, vitamin C, folic acid, organosulfides, isothiocyanates and protease inhibitors.

Most effective ways of preventing:

Consumption of diet high in vegetables

Regular physical activity

Low consumption of red and processed meat

Probably also important:

  • maintaining body weight
  • diets high in non-starch polysaccharides and carotenoids
  • diets low in sugar and fat


Journal of Women's Health