BMI: Better than your bathroom scale

With revenues of more than $30 billion a year, diet-industry coffers are full to bursting. Ironically, so are the seams of the more than one in two Americans who are overweight. That’s according to new federal guidelines that determine obesity based on body mass index (BMI) and waist circumference. Those two factors, in turn, are considered along with risk factors for obesity-related conditions, such as diabetes and high blood pressure, and a family history of heart disease.

A better measure

Both BMI and waist circumference are better measures of obesity than weight alone—BMI, because it indicates the percentage of body fat; and waist circumference, because it indicates how much fat is carried around the abdomen, in itself a predictor of heart disease.

Doing the math

To calculate BMI, use this formula:

1. Divide your weight (in pounds) by your height (in inches) squared.
2. Multiply the resulting number by 705.

Example for a woman who weighs 140 pounds and is 5’4", or 64" (to square, multiply 64 x 64):

1. 140/4,096 = 0.034
2. 0.034 x 705 = 23.97
3. BMI = 23.97

Interpreting the results

In the above example, the woman’s BMI falls at the upper end of the healthy range, which is 19 to 24. According to the new guidelines, a BMI of 25 to 29.9 is considered overweight, and a BMI of 30 or greater is considered obese.

In addition, women whose waists measure more than 35" and who have a BMI of 25 or greater are at increased risk for obesity-related illness.

If your BMI is high

Reducing your BMI to the desirable range should be a long-term goal, mainly because it takes time to make new nutrition and fitness habits stick. So focus on losing just 10 percent of your body weight over six months. To enhance your efforts, do about 30 minutes of aerobic activity, such as walking, swimming and cycling, every day. Be consistent, and over time you’ll see measurable results.