 Primary Objective To assess the feasibility of low-protein diet intervention in patients with metastatic CRPC receiving immunotherapy with sipuleucel-T. Change in blood urea nitrogen BUN and urine urea nitrogen UUN from baseline to 6 weeks will be measured to assess adherence of following the diet intervention. The expected changes mean, standard deviation in BUN are 5.5 2.6 mgdL with 10 protein diet arm and 2.5 2.6 mgdL with 20 protein diet arm please see section 12.5.7. 