Weight loss and gain is pretty simple really, if you consume too many calories in a day and don't burn them off with exercise you gain weight. If you eat the right amount of calories your body needs in a day, you will maintain your weight. The amount of calories your body needs can be measured by finding out your BMR (Basal Metabolic Rate) - I always understood it as the number of calories your body uses just to live. So to lose weight you need to eat slightly less calories than your body's BMR. Slightly less, not dramatically so, 1000 calories is way too little.
Calculate your BMR using one of the online calculators you can find. I Googled it and this was the first result:
http://www.bodybuilding.com/fun/bmr_calculator.htm
Start by eating 10-15% less and eating back the calories you burn. If you don't eat back the calories you burn with exercise, (it doesn't have to be ALL, but if you're hungry then you should eat - listen to your body) then you might find yourself feeling drained and your weight might stall. The more exercise you do, the more you should be eating. Athletes tend to eat 2000+ calories a day because of all the exercise they do - food is fuel remember, not the enemy! Being mindful of calories is a great thing, but make sure you're giving your body what it needs to keep functioning.