Although a scale can tell you your body weight, it cannot tell you what portion of your body is made up of fat versus bone, muscle, water, organs and other components. The estimate of your amount of body fat helps your doctor classify you as underweight, normal weight, overweight or obese. Your body fat percentage can have serious implications for your overall health and risks for various chronic diseases.
BMI Classifications
The most common index that health care providers use is the body mass index. Your BMI is your height-to-weight ratio, an indicator of the amount of body fat you have, explains the University of Pittsburgh Medical Center. Your health care provider interprets your BMI calculation to determine your weight status. If you have a BMI of less than 18.5, you're underweight, whereas a BMI of 18.5 to 24.9 is a normal weight range for adults, the Mayo Clinic says. A BMI of 25.0 to 29.9 is an overweight classification, and a BMI of 30.0 to 39.9 is considered obesity. If you have a BMI of 40.0 or higher, your weight classification is morbidly obese. To calculate your BMI and get a general idea of your body fat amount, divide your weight in kilograms by your height in meters squared.
Body Fat Percentage
Several methods are available for measuring your percentage of body fat, including testing with calipers. Calipers are clamp-like tools that measure the amount of fat beneath your skin at different parts of your body, says the University of Pittsburgh Medical Center. Bioelectrical impedance, the Bod Pod, underwater weighing and dual x-ray absorptiometry scans are less commonly used but more accurate measurement methods for body fat percentage. Depending on your age and gender, a healthy body fat percentage will vary. If you're a woman, your body fat should be 21 to 32 percent when you're 20 to 39 years old, 23 to 33 percent when you're 40 to 59 years old, and 24 to 35 percent when you're 60 to 79 years old or older. If you're a man, a healthy body fat percentage is just 8 to 19 percent when you're 20 to 39 years old, 11 to 21 percent when you're 40 to 59 and 13 to 24 percent when you're 60 to 79 or older.
Significance
Knowing your body fat classification through your BMI and body fat percentage is essential to understanding your overall health status and preventing or correcting obesity. Being overweight or obese can greatly increase your risks for type 2 diabetes, high blood pressure and other serious health problems, warns the Mayo Clinic. Conversely, maintaining a healthy weight and body fat percentage by eating a nutritious diet and staying physically active can reduce your risk for sleep apnea, stroke and coronary artery disease, says the University of Michigan Health System.
Considerations
Although BMI is a widely used classification tool for weight status, the index doesn't always give you an accurate account of your body fat, according to the University of Pittsburgh Medical Center. In fact, people who have lots of muscle mass may end up in an overweight or even obese category when they're actually quite lean. Also, some people may have a BMI and weight-to-height ratio that reflects a "normal" classification, although they're actually overweight and have little lean muscle mass. Also, your doctor may perform various other tests to determine your weight classification, such as a basic physical exam and blood tests to check your cholesterol, fasting glucose and thyroid-hormone levels, the Mayo Clinic notes. Your doctor might measure your waist circumference to determine how much abdominal fat you're carrying, which can indicate your risks for chronic obesity-related diseases. Women should have a waist circumference of no more than 35 inches, while men should have a waist measurement of less than 40 inches.
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