Erin, it depends on WHY you want / need that percentage of body fat. For professional body builders 15% or lower is normal - and necessary. You must keep in mind that they don't always have this % - during the off season things change.
At 17% body fat you would not look gross - you don't look gross now! You need to go to
www.bodychangers.com and take a look at what some of the women at 20% look like. You may be underestimating your % now if you think 17% wont make a difference for you. Having a low body weight doesnt mean that person has a low body fat - it just means they weigh less.
Starving yourself to a low body fat doesnt work - starvation = loss of muscle mass, muscle mass is what makes a lower % of body fat possible.
The average % of BF in the States for women right now is 28% - isnt that shocking? Normal/ healthy / desirable is between 22 - 26% depending on age.
For the average woman to get to 15% a lot of work and dedication is involved - it's tough and it's usually not something you sustain forever. For some it's just to be able to say "Look, I did it"
Menstruation can cease for many reasons; insufficient intake of calories, excessive exercise, and yes, body fat % - which can be all interconnected when you think about it. There seems to be a body fat threshold for the maintenance of normal cycles that is in the neighborhood of 18%. Amenorrhea may also result from psychogenic causes such as depression or chronic emotional stress.
I have a forumal here for calculating % of BF that is pretty accurate. I will hunt it down and post it for you.
Nat