And by 2000, I presume you mean 1500 or less. Most people's bodies can probably easily adjust to 2000 calories at something near their current weight. In fact, for most people who want to lose weight, it would probably be easier just to keep calories/day to "about 1000" rather than trying to hit a precise target like 1850 or whatever their height and build should require.
No, those numbers are way off. If you eat 1000 calories a day and are male, you will almost definitely be in poorer health. You will lose muscle and gain fat %, and while you may be "lighter", you will almost definitely be fatter.
Use fitday.com or something to ACTUALLY TRACK (yes, actually, as in EVERY DAY) the calories you eat. You can't "guess" something like this. Furthermore, google for 'daily caloric expenditure calculator' and find out exactly how much someone of your height and build is burning, and eat accordingly.
Of course you'll be in poorer health. You're losing weight, and if you keep it up you'll eventually starve. The process of "losing weight" has to be temporary. However, if you could determine the calorie count that would keep you stable at your desired weight, you will never be able to reach that weight on that calorie count (all else equal: no extra exercise, etc), because your body will lower metabolism enough that you'll level off above that.
I have lost weight in a sustained fashion to accomplish a goal just once in my life so far (~310 to 187 at my lowest; let's agree that I wasn't fatter at 187, eh?), and it would have taken years to drop it had I just started eating 2000 kcal a day. Even 2500 kcal is probably enough to maintain 300 lbs if you don't exercise and don't actively try to build muscle.
