How BMI Works
The BMI formula is the same for adults of all ages and factors in height and weight to determine if you fall within a normal weight range. To calculate your BMI, divide your weight in pounds by your height in inches squared, and multiply the result times 703: For example, a 5-foot-5 woman who weighs 140 pounds has a BMI of 23.8. A BMI of less than 18.5 is considered underweight, a BMI between 18.5 and 24.9 is normal, a BMI of 25.0 to 29.9 is considered overweight and a BMI of 30 and higher indicates obesity.
BMI After Menopause
In a study published in the journal "Anthropological Review" in 2013, researchers studied body weight and fat distribution in more than 10,000 women between 25 and 95 years old. They found that postmenopausal women had higher BMIs than premenopausal women, and that women stored more fat in their midsections after menopause. Researchers concluded that hormonal changes during menopause affect the way the body stores fat, and that postmenopausal women are at higher risk for weight-related illness.
Causes and Prevention
Although hormones may be to blame for extra belly fat after menopause, they probably aren't responsible for most weight gain, according to MayoClinic.com; lifestyle and genetic makeup have more effect on weight. As you grow older, your body loses muscle mass -- particularly if you're inactive -- which reduces your metabolism, or the rate at which you burn calories. To combat weight gain, engage in at least 150 minutes of aerobic activity each week, such as swimming, jogging or using an elliptical machine. You should also work on muscle-building activities, such as lifting weights or performing lunges, situps and pushups, at least twice weekly. You also may not be able to eat as much as you did in your youth without gaining weight; after age 50, most women burn about 200 fewer calories per day than in their 30s and 40s.
Although BMI is a useful tool, it doesn't offer much insight on body composition. Most obesity-related illnesses are linked to fat levels and not weight from muscle mass or other tissues -- and you may have a normal BMI but excess body fat, making you technically obese. This is more common among women than men, and you may be especially at risk if you lost significant muscle mass after menopause. For a more accurate picture of your health, request a body composition test from your physician.