it's ok to burn 1,000 calories every day eaven you dont'd eat 1,000 a day?

i'm asking that because i'm pre-op and they want me to loose 12 pounds in three weeks is that make any sense, i drink my slim fast milk shake plus my salads' few snacks and lots of water every day i cut basicly my carbs because thats what they got me do any more sugestion fell free to let me one thank's

Yes, it's okay. You have plenty of fat stores to provide energy and fuel your body.