If I eat 800 calories how many pounds will I lose? If I eat 800 calories how many pounds will I lose? A human body needs 1500 calories a day as Resting Metabolic Rate (RMR). This is the minimum energy needed by body to maintain proper functioning of its vital organs. So if you intend to eat only 800 calories. Your vital organs will start malfunctioning and you will not be able to recover from...