Background: Plant-based diets have many health benefits including a lower risk of fatal prostate cancer. Less is known about the relationship between diet and functional outcomes among prostate cancer survivors. We hypothesized that greater consumption of plant-based food after prostate cancer diagnosis is associated with improved quality of life (QOL). Methods: This prospective cohort study included 3,505 participants in the Health Professionals Follow-up Study with non-metastatic prostate cancer (1986-2016). Overall and healthful Plant-based Diet Indices were calculated from food frequency questionnaires with cumulative updating. QOL scores were calculated using the Expanded Prostate Cancer Index Composite. Generalized estimating equations were used to examine associations between Plant-based Diet Indices and 5 QOL domains, adjusted for clinical and demographic factors. Results: Higher Plant-Based Diet Index was associated with improved scores for sexual function, urinary irritation/obstruction, and urinary incontinence among men with prostate cancer. Consuming more healthful plant-based foods was also associated with better scores for bowel function and hormonal/vitality in the age-adjusted models. Results were similar in sensitivity analyses excluding patients with pre-existing erectile dysfunction or lower urinary tract symptoms, and adjusting for use of sexual or urinary medications. A limitation is that no participants followed a strict vegan diet. Conclusions: This prospective study suggests that greater consumption of healthful plant-based foods is associated with modest improvements in QOL domains among patients with prostate cancer.

Model 1 is adjusted for age and time. Model 2 is also adjusted for PSA, grade, stage, body mass index, physical activity, calories, smoking, alcohol, diabetes, heart disease, stroke and hypertension.