The Impact of Physical Activity Versus Dietary Energy Restriction on Tumour and Muscle Protein Synthesis in Prostate Cancer Patients

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 pro