You can still lose weight, but it will be very gradual. Never take in less than 1500 calories/day if you have a normal activity level, and try to do some heavier exercise. Instead of just walking, try running, or at least power/speed walking. You could also bike, or any other cardio activity, and it would help a lot. If you can keep your heart rate between 120-150 for at least half an hour at a time every day, you should start losing weight more rapidly.
