We have two main types of fat in our bodies:
1. Visceral fat, the kind that builds up around your organs. This is nasty stuff and one of the hallmarks of metabolic syndrome, a proven precursor to diabetes and heart disease.
2. Subcutaneous fat, the stuff you not-so-lovingly pinch on your hips and thighs. This type of fat does not seem to have the same health risks as visceral fat. In fact, a meta-analysis of existing research showed that women with larger hips and thighs have smarter babies, thanks to the type of fat stored there!
The trick, as with many fitness endeavors, is finding the sweet spot between too much and too little body fat.
No one wants to be "skinny fat" (thin but with little muscle) and with good reason. Muscle tissue, which weighs more than the same volume of fatty tissue thanks to its higher density (i.e. it's more tightly packed), not only makes you stronger, but research shows that increasing your lean muscle mass can help rev up your metabolism, boost bone mass, and even make you smarter. So while you may gain some weight as you put on more muscle, it's a good trade off--and the major reason why we need to kick the scale as our primary measure of health.
What About BMI?
BMI is a relatively straightforward equation that measures a person's body fat by comparing their weight to their height:
BMI = (Weight in pounds / (Height in inches x Heigh in inches)) x 703
There are four different categories a person can fall into, ranging from underweight to obese (Find your BMI without doing any math here).
One of the major problems with this formula is that it has no way of discriminating between fat and muscle. So while a world-class athlete may have very little body fat, there's a good chance he or she may be classified as "overweight" by BMI standards, thanks to years of training to build muscle mass.
So if you can't trust your scale or your BMI, what's a better option? A number every woman should know: your body fat percentage. And you don't necessarily need expensive tests or fancy equipment to find out.