Numbers to Live By

Body Mass Index

Healthy number: Between 18.5 and 24.9.

Your body mass index (BMI) is a measure of your weight in relation to your height (calculate yours at nhlbisupport.com/bmi). A BMI of less than 18.5 means you’re underweight and at risk for irregular periods, fertility problems, anemia, and the bone loss that can lead to osteoporosis. Many Americans, however, have the opposite problem: a BMI that is too high. If a person’s BMI is between 25 and 29.9, she is considered overweight. A BMI of 30 or higher is defined as obese—and that’s a problem that lasts long after bathing-suit season is over. “Obesity increases your risk for just about every disease,” says Klein. But BMI alone doesn’t tell the whole story; bear in mind that if you carry extra weight around your middle (say, your waist circumference is 35 inches or greater), you’re at risk for type 2 diabetes, heart disease, and all their attendant health issues, even if your BMI is in the normal range, notes Stephanie Faubion, an internist at the Mayo Clinic in Rochester, Minnesota.

Calculate yours: Annually, or after a weight gain or loss. If it’s too high, make an effort to eat less and exercise more. Keep a tape measure handy to track any waist changes as well.