So I was thinking about body composition and decided to run some numbers. My conclusions were pretty startling.
I've had my body fat taken 3 times using bioelectrical impedance. All three of these taken at school under similiar conditions (in clothes but minus shoes).
Humiliating forced weigh-in, spring 8th grade (14 y.o.)- 135lbs, 40% body fat ~5'1.5"
Sophmore PE, beginning of semester (15 y.o.)- 99lbs, 15% body fat ~5'2"
Sophmore PE, end of semester (almost 16)- 99lbs, 13.5% body fat
Please note: Having a body fat percentage that low is
not recommended for women. My lowest recorded body fat was a little lower than what's considered normal for athletes. My general practioner said I was fine because I had great lean muscle mass and experienced no adverse indicators (loss of period, hair and skin issues, etc.). In other words, do not attempt.
Obviously I lost 36lbs+ in that period, which I already knew. My estimated lean body mass was only 81lbs in the 8th grade. That means I was carrying an estimated 54lbs of fat!

What's more interesting to me than just the weight loss is that in the same period I added 5lbs of lean (non-fat) body mass. That means that teenage me was able to lose 41lbs of body fat by eating less and exercising more.
Now on to the bad news: I'm now in my mid-20s, and I'm definitely no size 0 anymore. I'm an extreme hourglass shape, so while my waist is a 6, my bust and hips are a 10 (based on the Gap's size charts). Although I've been exercising almost everyday for a couple months, I'm still a good 10lbs+ off from where I should be.
So what should I weigh? This was the orginal question that inspired me to run the numbers. First, I estimated my current lean body mass to be about 95lbs. I'm somewhere around an inch and a half taller than I was my sophmore year of high school. I've been lifting so I've probably add a little bit of muscle as well though I can't really lift any more than I did in high school. So here's the really terrible news: my ideal condition would probably be somewhere around 115lbs (20% body fat). An acceptable and more attainable weight for me would be around 125lbs. The most I should weigh would be around 130lbs as I highly doubt that I have more than 100lbs of lean body mass. I really have no idea how much I currently weigh, but I know it's more than 125. This is all depressing.
Do any of you know (or have a reasonable guess) what your lean body mass is? Is body fat a factor for you or are you more focused on weight or size or fitness level or how you look?