Calorie needs are different for everyone and depend on height, weight, side effects, and treatment. The estimated calorie needs for someone with cancer is 15 calories per pound of weight if your weight has been stable. Add 500 calories per day if you have lost weight. Example: If you weigh 150 lbs., you need about 2,250 calories per day to maintain your weight. A dietitian can help you know what you need and suggest ways to maximize your nutrition while you have prostate cancer.