Will eating 1000 calories a day cause weight loss?

Unless you are a kitten, eating less than 1200 calories a day will quickly make you so fatigued that you will be completely unable to exercise. For most people, you can eat something more like 1600-2,500 (subtract 500 calories from the total amount of calories required for you to maintain your weight) calories a day, and get an hour of cardiovascular exercise, and lose a healthy amount of weight. If you are going to do any serious weight lifting, like the sort that will burn more calories than cardio (moderate level weight lifting does increase base metabolism for 48 hours as opposed to 1-3 hours for cardio), then you will probably need something like 3,000 to 5,000 calories a day just to feel physically capable of completing your workouts. My advice, and I think anyone's advice here would be that if you want to do both you should do half an hour of intense cardio and follow it up with 30 minutes of solid weight lifting (clean and press, bench, squats, rows, deadlifts, overhead press 5X5 or something similar) and eat the amount of calories that you would need to eat to maintain your weight if you were NOT getting exercise. Then just pop a 5 hour energy or other stimulant before you hit the gym, and do your workout before sleep, after your last meal of the day. If you have insurance, go see your doctor. Not only can they check out your heart etc. before you get too serious, they can advise you how to safely lose weight fast. G'luck brah.