Diet and Physical Activity as Mediators of Weight Loss in a Digital Prostate Cancer Survivorship Intervention for Men: Secondary Analysis of the PC-PEP Randomized Trial.

Weight gain during prostate cancer treatment can worsen treatment-related side effects, impair quality of life, and increase risks of recurrence and prostate cancer-specific mortality. The Prostate Cancer Patient Empowerment Program (PC-PEP), a comprehensive, home-based 6-month digital intervention, has demonstrated improvements in diet, physical activity, and weight. This secondary analysis examined whether changes in diet and physical activity mediated weight loss among participants receiving PC-PEP. In a randomized clinical trial, 128 men with localized prostate cancer were assigned to PC-PEP (n=66) or standard care (n=62) for six months. Diet quality was assessed using a 12-item summary score reflecting weekly frequency of key food groups. Physical activity level was self-reported as not very active, moderately active, or very active. Mediation models were adjusted for age, comorbidity, treatment modality, time from randomization to treatment, relationship status, medication for anxiety or depression, and baseline weight, diet, and physical activity. The results show that weight loss in the PC-PEP group was significantly mediated by both diet and physical activity, accounting for 21% and 16% of the total effect, respectively. The direct effect of the intervention remained significant. These results indicate that improvements in diet and physical activity partially mediated weight loss in men receiving PC-PEP, while a substantial direct effect suggests that additional components of the intervention contribute to outcomes. Findings highlight the value of comprehensive, multi-faceted digital survivorship interventions for men with prostate cancer and suggest that observed mediation effects are conservative estimates given the use of brief self-reported behavioral measures.