Objective: We examined the relation between whole grains, fruit, vegetables and dietary fiber and colon cancer risk in the prospective Cancer Prevention Study II Nutrition Cohort.
Methods: In 1992-1993, 62,609 men and 70,554 women completed questionnaires on medical history, diet and lifestyle behaviors. After exclusions, we confirmed 298 cases of incident colon cancer among men and 210 among women through August 31, 1997.
Results: Multivariate rate ratios (RR) and 95% confidence intervals (CI) for all dietary factors were null. However, a statistically non-significant 30% reduction in risk was observed for men with the highest vegetable intakes (RR = 0.69, CI = 0.47-1.03, top versus bottom quintile, p trend = 0.10). Men with very low (lowest tertile within the lowest quintile) intakes of vegetables and dietary fiber were at increased risk compared to those in the highest four quintiles of intake (vegetables RR = 1.79, CI = 1.22-2.61, p trend = 0.04, and fiber RR = 1.96, CI = 1.24-3.10, p trend = 0.006). Women with very low intakes of fruit were also at increased risk (RR = 1.86, CI = 1.18-2.94, p trend = 0.06).
Conclusions: Higher intakes of plant foods or fiber were not related to lower risk of colon cancer. However, our data suggest that very low intakes of plant foods may increase risk, and that certain phytochemical subgroups may decrease risk.