colorectal cancer has been shown to be associated with increased total dietary fat and red meat consumption (Nurses Health Study, Health Professional’s Follow-Up Study)
a high ratio of red meat to chicken or fish also associates with an increased risk or colorectal cancer
no association is seen with vegetable fat
fat intake has also been linked to non-Hodgkin’s lymphoma; no link has been found to breast cancer
then again, other studies have shown no association at all (probably unreliable)
possible mechanisms
increased bile acid excretion
Þ
may be metabolized to carcinogens by intestinal flora
Þ
may accelerate mucosal cell turnover
increased fecal diglycerides
increased free radicals
Fiber
some studies support a protective role of fiber for colorectal cancer
large prospective studies have provided mixed results
Þ
protective effect may be from antioxidants or phytochemicals found in plants
possible mechanisms
dilution and binding of carcinogens and procarcinogens
binding of bile acids
decreased conversion of primary bile acids to secondary bile acids
fiber fermentation by bacteria Þ volatile fatty acids (acetate, butyrate)Þ ß pH Þ positive effect on epithelial cells
different sources of fiber seem to have different protective effects (i.e. grain vs. fruit fiber)
wheat bread is not necessarily high fiber
Antioxidants
help reduce free radicals
vit E: lipid soluble; vit C: water soluble
Phytochemicals
non-nutrients that may have protective effects
sulforaphane
(an isothiocyanate): found in cruciferous veggies (broccoli, cabbage)
induces phase II detoxification enzymes (i.e. glutathione-S-transferase)
reservatrol
(a phytoalexin): found in red grapes (and red wine)
antioxidant, antimutagen, phase II detox inducer
Cooking/Smoking Meat
high temperature cooking (produce charred/burnt surface) Þ heterocyclic amines (potential carcinogens)