Adherence to dietary and lifestyle recommendations and prostate cancer risk in the Prostate Testing for Cancer and Treatment (ProtecT) trial

Background: The World Cancer Research Fund (WCRF) and the American Institute for Cancer Research (AICR) published eight recommendations for cancer prevention but they are not targeted at prostate cancer prevention. We investigated whether adherence to the WCRF/AICR recommendations and a prostate cancer dietary index are associated with prostate cancer risk. Methods: We conducted a nested case-control study of 1,806 PSA-detected prostate cancer cases and 12,005 controls in the ProtecT trial. We developed a prostate cancer dietary index by incorporating three dietary factors most strongly associated with prostate cancer. Scores were computed to quantify adherence to the WCRF/AICR recommendations and the prostate cancer dietary index separately. Results: The prostate cancer dietary index score was associated with decreased risk of prostate cancer (OR per 1 score increment: 0.91, 95% CI: 0.84, 0.99; p-trend=0.04) but the WCRF/AICR index score was not (OR: 0.99, 95% CI: 0.94, 1.05; p-trend=0.82). There was no heterogeneity in association by prostate cancer stage (p=0.46) or grade (p=0.86). Greater adherence to recommendations to increase plant foods (OR per 0.25 index score increment: 0.94; 95% CI: 0.89, 0.99; p-trend=0.02) and tomato products (OR adherence vs. non-adherence: 0.82; 95% CI: 0.70, 0.97; p=0.02) were inversely associated with overall prostate cancer risk. Conclusions: Adherence to the prostate cancer-specific dietary recommendations was associated with decreased risk of prostate cancer. High intake of plant foods and tomato products in particular may help protect against prostate cancer. Impact: Meeting the WCRF/AICR recommendations alone is insufficient for prostate cancer prevention. Additional dietary recommendations should be developed.