Have single-digit body fat.

As mentioned, this is not generally healthy for women, (and some men), please consult a health professional if this is a goal that you are not sure about. Your safety and health is much more important than anything else. This is not a goal that should be associated with aesthetics. I maintain a balance of my fat and water levels that is appropriate for my body type through diet and exercise.

What’s the point? Longevity of life.

Not to discourage anyone, but I found the link below interesting. Basically it seems that it might be unhealthy for a woman to go below 10% body fat: Body Fat Chart