Losing weight faster than expected...body fat or muscle mass

bjlkt2

(X-posted in the fitness forum)

Hi all,

I've been on MFP for about two weeks, but to be honest, only started taking calorie tracking seriously starting last Saturday (so only 3 days). I've always been active and at a relatively healthy weight, but I decided I wanted to lose a little extra body fat to be leaner for a fitness photoshoot I'm doing with a friend in three weeks.

So, I set my weight-loss goal to 1.5lbs per week. Problem is, I've already lost almost 4 pounds in three days. Yeah, I realize part of this could just be water weight or something, and I'm probably over-reacting, but I just want to be sure that I'm not losing any muscle mass or anything.

Like I mentioned, I'm very active, lifting pretty serious weights (deadlifts, squats, etc) for about an hour and jogging 20 minutes or so, every other day. I've done this for several months, and am continuing to increase the weight I'm lifting. I'm meeting my net calorie goal, and I'm making sure to get enough protein (minimum 75g a day, up to about 100g; also, I'm 5'7" and 133lbs currently if that helps at all).

Anyway, I guess I was just under the understanding that if weight is lost that quickly (more than say, 2-3lbs per week) it's probably muscle mass being lost, not body fat. Is that true? Even though I'm lifting weights and getting enough protein? I really don't want to lose muscle mass, just body fat; should I be worried at dropping 4 lbs in 3 days?