Hi Jacque! I think you're mixing up BMI and body fat %. They are two very different things, so let me take a stab at explaining them.
is Body Mass Index. It's simply a height-weight correlation. 18 - 24 is considered normal weight, 25 - 29 is overweight, and over 30 is considered obese. We have a BMI calculator right here at 3FC: BMI Calculator
BMI is handicapped by the fact that it doesn't distinguish between pounds of fat and pounds of muscle (it just uses total weight) so that's where Body Fat Percent
(BF%) comes into play. Your BF% tells you how many pounds of fat are on your body and how many pounds of Lean Body Mass (LBM), which is everything in your body that isn't fat - bone, hair, skin, water, and muscle
(the significant part).
The ranges for BF% for women are as follows: 32% and above is considered obese (or "high risk", which is a nice way of saying obese), 25 - 31% is acceptable (or normal), 21 - 24% is considered a "fitness" level, 14 - 20% is "athletic", and under 12 - 13% starts to compromise essential body fat. There are different ranges and names for the categories, but this is what the American Council on Exercise (ACE) uses.
Once your weight is in the normal range, BF% is a much better indicator of your fitness level than scale weight. You can have two women - same age, height, and weight - and one can have a BF% of 18% and the other 30%. The one with more muscle and less fat will be several sizes smaller than the other because muscle takes up much less room than fat. And she'll be tighter and a whole lot less flabby! Yay, muscle!
It sounds like your body fat % was tested at Canyon Ranch, not your BMI. 17% is a great result! Handheld testers use bioelectrical impedance and probably aren't as accurate as a nine-site caliper test in the hands of an experienced operator, but they're a fast and easy way to track trends in your body composition over time.
Bottom line -- forget BMI and start tracking body composition by checking your body fat percentage.