Low bodyfat through diet alone doesn't really work all that well. Without excercise, women don't really have much muscle, so someone with little muscle and low bodyfat looks like a runway model. All angle, no curve, no nice "cut" looking arms.

Most slender women (thin, but not runway model thin) actually have high bodyfat percentages. I wear an 8/10 and have 20% bf, my best friend (totally sedentary) wears a 2/4 and has 30% bodyfat, but she looks thinner.