| Summary: | Background. Previous studies have analysed total carbohydrates as a dietary risk
factor for colorectal cancer (CRC), but obtained conflicting results, perhaps due
in part to the embedded negative confounder, fiber. The aim of this study is to
analyse the non-fiber ("effective") carbohydrate component (eCarb) separately,
and to test the hypothesis that effective carbohydrate consumption is direcdy
related to colorectal cancer risk. Method. The data (473 cases, 1192 controls) are
from a large, multi-centre case-control study of migrant Chinese. Multivariate
logistic regression was used to perform a secondary analysis, controlling for age,
fat, protein, fiber, physical inactivity, calcium, retinol, body mass index, family
history, education, years in North America, and for women, parity, age at
menopause, hormone replacement therapy use and oral contraceptive use. The
model was used to calculate odds ratios (OR) and 95% confidence intervals (CI)
to estimate risk from increasing eCarb consumption among subgroups by gender
and cancer site. Results. A statistically significant positive association was
observed between eCarb consumption and risk of CRC in both males (OR=2.02
from lowest to highest fertile of eCarb consumption, 95%CI=1.28, 3.19) and
females (OR=2.54, 95%CI-1.44, 4.46). A striking gender difference in cancer
site affected was observed, with risk concentrated in the right colon for women
(OR=7.35, 95%CI=2.60, 20.80), and in the rectum for men (OR=2.78, 95%CI=
1.40, 5.54). The other-sites for each gender showed little or no significant
association of eCarb consumption with risk. Onset of menopause had a
significant protective effect, and there was a near-significant interaction of
menopause with eCarb consumption (p=0.07). Conclusion. Increased eCarb
consumption is associated with increased risk of colorectal cancer in both
genders. The right colon risk is greatest in females, while the rectal risk is greatest
in males. In females, colorectal cancer risk may be reduced by onset of
menopause.
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