Weight Loss

Is a daily deficit of 900-1000 cals on an on going basis going to slow my metabolism? I'm aiming for a lb per week drop and only see this result by sticking with such high deficits, is this a sign it has already slowed? I know a 1-2lb loss per week is healthy, and a 2lb loss would indicate a 1000 cal deficit per day. I really dont want to slow it down and ruin it in the long term for a short term effect.. any advice?

It rather depends on where a 1000 cal deficit takes you.  If you're very obese and taking in 2000 cals to get a 1000 cal deficit it probably wouldn't have as big an impact as if you're simply overweight, eating 1200 and burning 2200.

If you can't lose weight except with a 1000 cal deficit then make sure the calculations are correct. i.e.  either burning less than you think or eating more than you think. 

It may be that with a 19BMI and eating less than 1200 calories per day (or thereabouts) you may have trouble shedding more weight without increasing activity and calories. What's your exercise regimen and your daily calorie intake?

Well my BMR is 1750 without exercise, and usually I will walk for an hour and half to and from work, burning approx 300, so thats 2000 burned say, and in the evenings I might run for 40 mins so thats about 400 cals burned. I eat about 1300-1400 cals weekdays and about 1700 saturdays and sundays, those days I wouldnt workout either, so really I have a 1000 deficit 4/5 days, I'm happy enough to lose at a 1lb p/wk rate, but I want to make sure I'm not messing up my metabolism, I understand the effects of starvation mode and do not want to go there! thanks for the advice!