Background: Prostate cancer is the second most common cancer and the fifth leading cause of death in men worldwide. Tumour growth is attributed to disproportionately greater protein synthesis rates relative to protein breakdown rates. Tumour protein synthesis is modulated by several factors, including energy availability, blood flow, and hormone concentrations (e.g., IGF-1). Lifestyle modifications are rapidly becoming recognized as important adjunct therapeutic approaches to slow cancer development and enhance treatment efficacy. Dietary energy restriction is a 30-50% reduction in food intake, which induces an energy deficit and has been shown to attenuate tumour growth in rodent models. Muscle mass often declines during cancer treatment and negatively impacts treatment success rates and recovery. One drawback to dietary energy restriction is that it may accelerate declines in skeletal muscle mass and strength in cancer patients. Exercise also induces an energy deficit by increasing energy expenditure. In addition, exercise alters blood flow and releases circulating molecules, which appear to lower tumour protein synthesis rates. Exercise increases muscle protein synthesis rates, which would provide further benefits to cancer patients by helping to maintain skeletal muscle mass. Despite their promising therapeutic properties, the clinical efficacy of dietary energy restriction and exercise has not been directly determined in vivo in cancer patients. Hypothesis and

Objectives: The objective of this study is to compare the impact of dietary energy restriction versus (isocaloric) daily exercise on muscle, prostate, and prostate tumour protein synthesis rates over a 7-day period in vivo in prostate cancer patients. It is hypothesized that 1) dietary energy restriction will lower both prostate tumour and muscle tissue protein synthesis rates and that 2) daily exercise will lower prostate tumour protein synthesis rates but increase muscle protein synthesis rates in prostate cancer patients. Setting and

Methods: Forty-five prostate cancer patients scheduled to undergo radical prostatectomy will be randomly assigned to one of three groups. The first group will undergo 7 days of dietary energy restriction (40% less food intake). The second group will perform 7 days of daily exercise and mild dietary energy restriction resulting in a total energy deficit of 40%. The third group will follow their regular diet and physical activity (control group). The research team will provide all aspects of the intervention (standardized meals, personalized exercise supervision). Patients will ingest deuterium-labelled water (2H2O) throughout the intervention period. After 7 days, patients will undergo a radical prostatectomy, during which tumour tissue, skeletal muscle tissue, and blood will be collected. Deuterium (2H-alanine) incorporation into the tissue samples will be measured to assess prostate tumour and skeletal muscle tissue protein synthesis rates.