You're asking and I'm answering . . .
"Fit, so I've been working out 5 days a week, and I'm only eating around 1000 calories a day and I can't seem to lose the weight. What gives?"
- Frustrated Fiona
To see my answer, read more.
What gives is that your body is probably starving. Granted I don't know your statistics, but 1,000 calories is not a lot, and you must be hungry! Here is the thing that so many dieters fail to accept: if you cut out too many calories, your body goes into starvation mode, which means your metabolism starts to conserve energy, slows down, and doesn't burn calories as fast — the exact opposite of your goal. You should always (always, always, always) be eating at least enough calories to match your resting metabolic rate or BMR (basically what the amount of calories you'd burn if you didn't get off your couch for a day). Here's a calculator if you don't know it — mine is around 1500, just to give you an idea. Clearly, since you're working out five days a week, you're going to need more than your BMR, as you're not a couch potato.
Check out my calculator to see how many calories you should be taking in given certain amounts of activity. So stop starving yourself and you should see a difference, you'll definitely feel one.