In today's society, the media focus on celebrities and whether they lose or gain a pound, so it's hard to grasp the idea of a healthy weight.

Obesity is determined by percentage of body fat and weight, according to the National Heart, Lung and Blood Institute (NHLBI). Having a large percentage of body fat, regardless of how much you weigh, is unhealthy. You could be of normal weight or underweight and still have an unhealthy amount of body fat. Being overweight means that you have a heavy weight, but not necessarily too much body fat. People who are muscular weigh more than those who are not. Their extra weight comes from muscle, not body fat.

According to NHLBI guidelines, an evaluation of whether you are overweight involves using 3 key measures:

• Body mass index (BMI)

• Waist circumference

• Risk factors for diseases and conditions associated with obesity. These include high blood pressure, coronary artery disease, high level of LDL ("bad") cholesterol, high triglycerides, high blood sugar, and smoking.

## Body mass index

The first measurement to find out whether you are overweight or obese involves determining your body mass index, or BMI. To calculate your BMI, multiply your weight in pounds by 703, then divide by your height in inches. Divide by your height in inches again.

BMI = (                 Weight in Pounds                             )   X  703

(Height in inches) X (Height in inches)

For example, if you weigh 162 pounds and are 69 inches (5 feet 9 inches) tall, your BMI is 23.9, or (162 x 703) ÷ (69 x 69), and is normal.

• A BMI of 18.4 or below: Underweight

• A BMI of 18.5 to 24.9: Normal

• A BMI of 25 to 29.9: Overweight

• A BMI of 30 or greater: Obese

For people who are considered obese or those who are overweight and have 2 or more risk factors (like high blood pressure, diabetes, abnormal blood fats, smoking, or coronary artery disease), the NHLBI guidelines recommend losing weight.

Although BMI is a reliable indicator of total body fat, it does have some limits. It may overestimate body fat in athletes and others with a muscular build. It may underestimate body fat in older adults and in others who have lost muscle mass.

## Belly fat or waist circumference

Another way to determine whether you are obese or overweight is to measure your belly fat. This can predict the risk for diseases associated with obesity. Determine your waist circumference by placing a measuring tape snugly around your waist. Your waist circumference is a good indicator of your belly fat. Your risk for diseases related to obesity increases with a waist measurement of more than 40 inches in men and more than 35 inches in women.

You should use your belly fat measurement along with your BMI to determine your risk. People who are overweight (BMI of 25 to 29.9), but don't have a large waist measurement and have fewer than 2 risk factors may need only to prevent additional weight gain rather than to lose weight.

If you are overweight and have other risk factors for diseases related to obesity, you should lose weight. If you are obese, you should lose weight even if you have no other risk factors.

## Skin fold thickness

A third way to determine whether you are obese or overweight is to have your skin fold thickness measured. This measurement is taken around the triceps (muscles of the upper arm), on the shoulder blades, and on the hips. The results can determine whether your weight is from muscle or from fat.

The BMI method is generally preferred because BMI shows a more accurate representation of total body fat that includes both height and weight, the NHLBI says. For the best determination of whether you're at a healthy weight, talk to your health care provider. Your health care provider will consider both your personal health and family history.