How do you lose muscle mass sanely/safely?

As in, without me turning into a bag of lard.

My point of insanity is that I seem to be gaining weight slowly(like 1lb to 1.5lbs, over 3 or so weeks), but my measurements have not changed or gone down. (Waist is down .5 inches, legs more muscular by a bit).

So I'm not getting fatter, but I'm getting a little heavier, or at least staying the same or similar? @.@

I am 6', 170lbs-large frame, 19, and female. I would like to trim about 8-12 lbs more off, no more, and stay the same or better body fat percentage. I haven't actually gotten a body fat testing in a long time, but I know my measurements have improved a lot.

I eat...probably 30% protein 20-25% fat, and the rest carbs, and about 2000-2200 calories. Dessert once a week, minimal white flour, no juice/soda. I started doing this after I noticed I was on a 2 month plateau, and tried to break it by making my calories closer to my "maintenance".

Is it because of my new workout routine? As of 3 weeks ago I started throwing in once a week HIIT on the treadmill for 25 minutes, followed by 30-40 minutes of moderate to heavy weight lifting. Followed by moderate "supersets", I would alternate say chest presses and walking lunges 3 times each no stopping, then move on to another group.

I've read that supersets are very good for gaining mass, but I don't particularly eat low carb, and I'm definitely...not a guy. I always thought gaining mass would be my absolute last problem, since my arms and legs have always been thin for my height(arm=10-11" unflexed, thigh=23")

Or is it something else???

Edit: Why I'm asking to lose a bit of muscle with the fat is that I would really like to get back to my endurance running. I have low arches, and large frame or not, I can never run completely pain free anymore, distance wise.

Lift less, run more, and eat less than you burn - that'll help you lose muscle.

It's not something that I like recommending, but if your goal is endurance running, I suppose that's the answer.

Also, read No Business Running - it has a recommended workout for runners to help strengthen you to reduce the chances of injury.

Original Post by fadedsunrise:

Is it because of my new workout routine? As of 3 weeks ago I started throwing in once a week HIIT on the treadmill for 25 minutes, followed by 30-40 minutes of moderate to heavy weight lifting. Followed by moderate "supersets", I would alternate say chest presses and walking lunges 3 times each no stopping, then move on to another group.

Just wanted to add that you should NOT do intense cardio prior to lifting heavy weights.  You are risking injury by doing so, and you're also diminishing your ability to lift heavy.  If you want to do both in the same gym trip, do HIIT after the lifting.  It's best to do them on different days or at least at different times, though.

Also, you likely WILL lose some muscle when you lose weight, despite eating protein and lifting heavy.  Most people lose about 75% fat / 25% muscle.  I've been lifting heavy and eating well the last 5 months and my approximate loss has been 86% / 14%.  I would stick with your plan, which sounds good other than the order, and give it a bit more time.  It's possible that you gained some muscle, but more likely it's just fat loss + water retention giving you smaller measurements and higher weight.