Plant-Based Diets and Disease Progression in Men With Prostate Cancer.

IMPORTANCE: Plant-based diets are associated with many health and environmental benefits, including primary prevention of fatal prostate cancer, but less is known about postdiagnostic plant-based diet patterns in individuals with prostate cancer.

OBJECTIVE: To examine whether postdiagnostic plant-based dietary patterns are associated with risk of prostate cancer progression and prostate cancer-specific mortality.

DESIGN, SETTING, AND PARTICIPANTS: This longitudinal observational cohort study included men with biopsy-proven nonmetastatic prostate cancer (stage ≤T3a) from the diet and lifestyle substudy within the Cancer of the Prostate Strategic Urologic Research Endeavor (CaPSURE) enrolled at 43 urology practices across the US from 1999 to 2018. Participants completed a comprehensive diet and lifestyle questionnaire (including a validated food frequency questionnaire [FFQ]) between 2004 and 2016. Data were analyzed from August 2022 to April 2023.

EXPOSURES: Overall plant-based diet index (PDI) and healthful plant-based diet index (hPDI) scores were calculated from the FFQ.

MAIN OUTCOMES AND MEASURES: The primary outcome was prostate cancer progression (recurrence, secondary treatment, bone metastases, or prostate cancer-specific mortality). The secondary outcome was prostate cancer-specific mortality.

RESULTS: Among 2062 participants (median [IQR] age, 65.0 [59.0-70.0] years), 61 (3%) identified as African American, 3 (<1%) identified as American Indian or Alaska Native, 9 (<1%) identified as Asian or Pacific Islander, 15 (1%) identified as Latino, and 1959 (95%) identified as White. Median (IQR) time from prostate cancer diagnosis to FFQ was 31.3 (15.9-62.0) months after diagnosis. During a median (IQR) follow-up of 6.5 (1.3-12.8) years after the FFQ, 190 progression events and 61 prostate cancer-specific mortality events were observed. Men scoring in the highest vs lowest quintile of PDI had a 47% lower risk of progression (HR, 0.53; 95% CI, 0.37-0.74; P for trend = .003). The hPDI was not associated with risk of progression overall. However, among 680 individuals with Gleason grade 7 or higher at diagnosis, the highest hPDI quintile was associated with a 55% lower risk of progression compared with the lowest hPDI quintile (HR 0.45; 95% CI, 0.25-0.81; P for trend = .01); no association was observed in individuals with Gleason grade less than 7.

CONCLUSIONS AND RELEVANCE: In this cohort study of 2062 men with prostate cancer, higher intake of plant foods after prostate cancer diagnosis was associated with lower risk of cancer progression. These findings suggest nutritional assessment and counseling may be recommended to patients with prostate cancer to help establish healthy dietary practices and support well-being and overall health.