Honestly, if you drop down to 1000 calories a day you'll lose weight initially, but then your body will most go into starvation mode, holding onto every ounce of fat it has, and you won't lose another pound.
I don't know much about weight loss but I do know that 1000 calories is too low because they say you should eat @ least 1200
calories daily. You can eat your weight in calories and lose weight just by doing that and each pound that you lose you adjust your calories accordingly.
for ex: if you weigh 190 pounds you eat 1900 calories daily those calories are just to keep your heart pumping.
all the extra calories you burn will aid in your weight loss so when you lose 5lbs you start eating 1850 daily and so on...easier said than done. I know.