Dietary Fat Intake and Mortality Among Patients With Nonmetastatic Prostate Cancer.

IMPORTANCE: There are 3.5 million prostate cancer survivors in the US, with a need for evidence-based lifestyle recommendations that improve survivorship. OBJECTIVE: To assess whether consumption of specific dietary fats after diagnosis is associated with long-term survival among patients with nonmetastatic prostate cancer. DESIGN, SETTING, AND PARTICIPANTS: This study, nested in the Health Professionals Follow-Up Study, a cohort of male health professionals from across 50 US states ongoing since 1986, included participants with confirmed nonmetastatic prostate cancer between 1986 and January 2019, followed up through December 2022. Statistical analysis was conducted from July 2024 to May 2026. EXPOSURES: Dietary data were collected every 4 years from validated food frequency questionnaires and used to estimate intake of saturated, polyunsaturated, monounsaturated, trans, plant, and animal fat after cancer diagnosis. MAIN OUTCOMES AND MEASURES: Main outcomes were all-cause mortality and death from prostate cancer, other cancers, cardiovascular disease, and other causes during a median 12.8 years (IQR, 8.1-16.8 years) of follow-up through 2022. Hazard ratios (HRs) and 95% CIs from multivariable Cox proportional hazards regression and multivariate nutrient-density models examined associations with mortality, adjusting for demographic, epidemiologic, and clinical factors. RESULTS: Among 4884 patients with nonmetastatic prostate cancer, the mean (SD) age at diagnosis was 69.5 (6.9) years. During follow-up, 3040 deaths from any cause were confirmed. When comparing patients in the highest quintile of saturated fat consumption with those in the lowest quintile, higher postdiagnostic saturated fat intake was associated with greater all-cause (HR, 1.24 [95% CI, 1.05-1.47), cardiovascular (HR, 1.42 [95% CI, 1.02-1.98]), and other cancer mortality (HR, 1.42 [95% CI, 0.93-2.17]). Animal fat, a major source of saturated fats, was also positively associated with all-cause mortality (HR, 1.14 [95% CI, 0.97-1.33]), as well as deaths from other cancers (HR, 1.49 [95% CI, 1.00-2.21]). Replacing 10% of calories from animal fats with plant-based fats (HR, 0.84 [95% CI, 0.76-0.93]) and replacing 5% of calories from saturated fats with monounsaturated fats (HR, 0.80 [95% CI, 0.70-0.91]) was associated with a decrease in all-cause mortality. There were no associations between dietary fats and prostate cancer mortality. CONCLUSIONS AND RELEVANCE: In this cohort study of patients with nonmetastatic prostate cancer, saturated fats, including animal fats, were associated with greater all-cause mortality owing to deaths from cardiovascular disease and other cancers. Diets rich in monounsaturated and polyunsaturated fats and plant-based fats after prostate cancer diagnosis were associated with improved survival outcomes for patients. These findings support evidence-based recommendations for patients and clinicians around dietary fat consumption to improve survivorship outcomes in the clinical setting of nonmetastatic prostate cancer.