Dietary fiber and colorectal cancer risk: a nested case-control study using food diaries.
BACKGROUND
Results of epidemiological studies of dietary fiber and colorectal cancer risk have not been consistent, possibly because of attenuation of associations due to measurement error in dietary exposure ascertainment.


METHODS
To examine the association between dietary fiber intake and colorectal cancer risk, we conducted a prospective case-control study nested within seven UK cohort studies, which included 579 case patients who developed incident colorectal cancer and 1996 matched control subjects. We used standardized dietary data obtained from 4- to 7-day food diaries that were completed by all participants to calculate the odds ratios for colorectal, colon, and rectal cancers with the use of conditional logistic regression models that adjusted for relevant covariates. We also calculated odds ratios for colorectal cancer by using dietary data obtained from food-frequency questionnaires that were completed by most participants. All statistical tests were two-sided.


RESULTS
Intakes of absolute fiber and of fiber intake density, ascertained by food diaries, were statistically significantly inversely associated with the risks of colorectal and colon cancers in both age-adjusted models and multivariable models that adjusted for age; anthropomorphic and socioeconomic factors; and dietary intakes of folate, alcohol, and energy. For example, the multivariable-adjusted odds ratio of colorectal cancer for highest vs the lowest quintile of fiber intake density was 0.66 (95% confidence interval = 0.45 to 0.96). However, no statistically significant association was observed when the same analysis was conducted using dietary data obtained by food-frequency questionnaire (multivariable odds ratio = 0.88, 95% confidence interval = 0.57 to 1.36).


CONCLUSIONS
Intake of dietary fiber is inversely associated with colorectal cancer risk. Methodological differences (ie, study design, dietary assessment instruments, definition of fiber) may account for the lack of convincing evidence for the inverse association between fiber intake and colorectal cancer risk in some previous studies.
Dahm
Christina C
CC
Department of Public Health and Primary Care, University of Cambridge, Cambridge CB1 8RN, UK.
Keogh
Ruth H
RH
Spencer
Elizabeth A
EA
Greenwood
Darren C
DC
Key
Tim J
TJ
Fentiman
Ian S
IS
Shipley
Martin J
MJ
Brunner
Eric J
EJ
Cade
Janet E
JE
Burley
Victoria J
VJ
Mishra
Gita
G
Stephen
Alison M
AM
Kuh
Diana
D
White
Ian R
IR
Luben
Robert
R
Lentjes
Marleen A H
MA
Khaw
Kay Tee
KT
Rodwell Bingham
Sheila A
SA
D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D015179:Colorectal Neoplasms / Q000453:epidemiology* / Q000209:etiology / Q000517:prevention & control; D015986:Confounding Factors, Epidemiologic; D015930:Diet Records; D004043:Dietary Fiber / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D018570:Risk Assessment; D012307:Risk Factors; D012737:Sex Factors; D006113:United Kingdom / Q000453:epidemiology