40% to 50%...
...carbohydrates is pretty normal for weight loss. Unless you are on a super low Carb diet. 1000 cals is low, but according to my MD as long as you don't keep at that level for months, you will be OK, just remember to take a multi-vitamin. You will also have to be super conscience of what you eat. It can be hard getting enough fiber and constipation is a common side effect. Use fitday to keep your protein at at least 30% so you don't compremise muscle while you are losing. It is after all the fat that you are after here.
Good luck, and if you find yourself stuck at a weight for more that 2 weeks or bored to tears with the foods you are allowed, or just hungry all the time, up your intake to 1200 to 1300, which should be OK for continued loss.