Summary of Evidence
High Fat Diet
Fiber, Fruits, and Vegetables
Nonsteroidal Anti-Inflammatory Drugs
Cigarette Smoking
Postmenopausal Hormone Use
Colonoscopy
Note: Separate PDQ summaries on Screening for Colorectal Cancer; Colon Cancer
Treatment; and Rectal Cancer Treatment are also available.
High Fat Diet
Epidemiologic, experimental (animal), and clinical investigations suggest that
diets high in total fat, protein, calories, alcohol, and meat (both red and
white) and low in calcium and folate, are associated with an increased
incidence of colorectal cancer.
Levels of Evidence - 3aii: Evidence obtained from well-designed and conducted cohort or case-control
analytic studies, preferably from more than one center or research group, that
have a cancer incidence endpoint.
- 4aii: Ecologic (descriptive) studies that have a cancer incidence endpoint.
Fiber, Fruits, and Vegetables
Cereal fiber supplementation and diets low in fat and high in fiber, fruits,
and vegetables, however, do not reduce the rate of adenoma recurrence over a
3-year to 4-year period.
Level of Evidence - 1b: Evidence obtained from at least one well-designed and conducted randomized
controlled trial that has a generally accepted intermediate endpoint
(adenomatous polyps) for studies of colorectal cancer prevention.
Nonsteroidal Anti-Inflammatory Drugs
Nonsteroidal anti-inflammatory drugs including piroxicam, sulindac, and aspirin
may prevent adenoma formation or cause adenomatous polyps to regress in individuals with prior colorectal cancer or adenomatous polyps and in the
setting of familial adenomatous polyposis.
Levels of Evidence - 1b: Evidence obtained from at least one well-designed and conducted randomized
controlled trial that has a generally accepted intermediate endpoint
(adenomatous polyps) for studies of colorectal cancer prevention.
- 3ai,3aii: Evidence obtained from well-designed and conducted cohort or
case-control analytic studies, preferably from more than one center or research
group that have cancer mortality and cancer incidence endpoints.
Cigarette Smoking
Cigarette smoking is associated with an increased tendency to form adenomas and
develop colorectal cancer.
Level of Evidence - 3aii: Evidence obtained from well-designed and conducted cohort or case-control
analytic studies, preferably from more than one center or research group that
have a cancer incidence endpoint.
Postmenopausal Hormone Use
Postmenopausal female hormone use is associated with a decreased risk of colon
cancer but not rectal cancer.
Level of Evidence - 3aii: Evidence obtained from well-designed and conducted cohort or case-control
analytic studies, preferably from more than one center or research group with a
cancer incidence endpoint.
Colonoscopy
Colonoscopy with removal of adenomatous polyps may reduce the risk of
colorectal cancer.
Level of Evidence - 3ai: Evidence obtained from well-designed and conducted cohort or case-control
analytic studies, preferably from more than one center or research group that
have a cancer mortality endpoint.
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