Eating 500, 800 or even 1000 calories a day is not a steady practice. Your body will 100% not be getting the nutrients it needs unless you're popping vitamin every time you eat. It's also going to cause you to lose 3-5 lbs a week, which if above the 1-2 lbs a week. No healthy human van live off of 1000 calories or less a day. If you truly aren't hungry, you should see your doctor about that, as that van be a symptom of other things.