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Clinical Question:
Does a diet high in fiber reduce the risk of colorectal cancer?
Bottom Line:
In this large pooled analysis, dietary fiber intake was inversely associated
with risk of colorectal cancer in age-adjusted analyses. However, after
accounting for other dietary risk factors, high dietary fiber intake was not
associated with a reduced risk of colorectal cancer.
Reference:
Park Y, Hunter DJ, Spiegelman D, et al. Dietary fiber intake and risk of
colorectal cancer: A pooled analysis of prospective cohort studies. JAMA
2005;294:2849-57.
Study Design:
Meta-analysis (other)
Synopsis:
Inconsistent findings from observational studies have continued the
controversy over the effects of dietary fiber on colorectal cancer. To
evaluate the association between dietary fiber intake and risk of colorectal
cancer. From 13 prospective cohort studies included in the Pooling Project
of Prospective Studies of Diet and Cancer, 725,628 men and women were
followed up for 6 to 20 years across studies. Study- and sex-specific
relative risks (RRs) were estimated with the Cox proportional hazards model
and were subsequently pooled using a random-effects model. Incident
colorectal cancer. During 6 to 20 years of follow-up across studies, 8081
colorectal cancer cases were identified. For comparison of the highest vs
lowest study- and sex-specific quintile of dietary fiber intake, a
significant inverse association was found in the age-adjusted model (pooled
RR = 0.84; 95% confidence interval [CI], 0.77-0.92). However, the
association was attenuated and no longer statistically significant after
adjusting for other risk factors (pooled multivariate RR = 0.94; 95% CI,
0.86-1.03). In categorical analyses compared with dietary fiber intake of 10
to <15 g/d, the pooled multivariate RR was 1.18 (95% CI, 1.05-1.31) for less
than 10 g/d (11% of the overall study population); and RR, 1.00 (95% CI,
0.85-1.17) for 30 or more g/d. Fiber intake from cereals, fruits, and
vegetables was not associated with risk of colorectal cancer. The pooled
multivariate RRs comparing the highest vs lowest study- and sex-specific
quintile of dietary fiber intake were 1.00 (95% CI, 0.90-1.11) for colon
cancer and 0.85 (95% CI, 0.72-1.01) for rectal cancer (P for common effects
by tumor site = .07).
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