This is a 2-arm randomized controlled feasibility trial among 40 overweight or obese men newly diagnosed with prostate cancer who are scheduled for prostatectomy. This study will use the presurgical period to explore the potential impact of weight loss via a healthy energy-restricted diet and increased physical activity on circulating hormones, cytokines, and growth factors, as well as effects on tumor biology and other clinical outcomes. Consenting patients will be block randomized to 1-of-2 study arms: 1) a healthful diet + exercise intervention to promote a weight loss of up to 2 pounds/week; or 2) a wait-list control who will receive the intervention once the study period is complete. Both groups will receive nutritional counseling during the study period to correct nutritional deficiencies with food sources. This study will explore and contrast changes in body mass index (BMI) observed over the study period (minimum of 3.5 weeks) in the intervention vs. wait-list control arms, and also monitor changes in body composition, energy intake and physical activity; these changes will be studied in relation to the following endpoints: a) changes in select circulating biomarkers and gene expression related to cancer progression, hormonal status, inflammation and other energy-related factors; b) rates of tumor proliferation and apoptosis; c) tumor immunohistochemical markers of insulin receptor, vascular endothelial growth factor (VEGF), AKT, and nuclear factor kappa-light-chain-enhancer of activated B cells (NFkB); and d) functional and health-related outcomes, i.e., side-effects and medical outcomes, quality of life (QoL), and functional status.