Body Mass Index

What Is It

BMI stands for Body Mass Index. As a way of managing weight and a healthy lifestyle, BMI can help you determine your potential risks for disease. BMI is calculated from a person’s height and weight. The resulting number is a fairly reliable indication of the amount of fat on a person’s body.

Other methods of determining body fat include dual energy x-ray absorptiometry and underwater weighing. Both of these methods are expensive and must be performed under the guidance of a physician.

Research has shown that BMI calculations provide a reliable indication of body fat without the need for invasive and direct measurements. It is important to note, however, that BMI is only one factor that should be considered when evaluating your health.

How is it calculated

BMI is calculated based on your height and weight. After determining these 2 figures, use the following formula: weight (lb) / [height (in)]2 x 703. For example, for a person who is 6′ tall and weighs 200 pounds, the formula would look like this: [200/ 72×72] x 703. The resulting number, or the BMI, is 27.12. For males and females over the age of 20, a standard interpretation of BMI is used:

Below 18.5 BMI is underweight

18.5-24.9 BMI is normal

25.0-29.9 BMI is overweight

30.0 and above BMI is obese

Why Is It Important

BMI is used by health professionals to determine whether a person is considered overweight; being overweight or obese leads to risk factors for other diseases and illnesses. As an initial screening tool, the physician will often follow up with other diagnostic tests such as an evaluation of diet and physical activity, family history and skinfold thickness measurements. Some diseases have an increased risk for people who are overweight or obese. Some of these include stroke, sleep apnea, hypertension, coronary heart disease and type 2 diabetes.

BMI is only one screening tool used in determining the state of your health. Even someone with a BMI in the normal range could have an increased risk if he does not get regular exercise, does not eat healthy foods and smokes cigarettes. Regardless of your BMI, making choices that include healthy eating and daily exercise is an important step in maintaining and improving your health.


BMI is considered a highly effective screening tool with a few notable exceptions. First, the BMI interpretations are different for children and teens. While BMI for children and teens is calculated with the same formula, the interpretation varies based on sex and age.

This accounts for differences as children and teens mature into an adult body. The second exception is for athletes. Athletes and other people with a large amount of muscle mass will often have a higher BMI. In these cases, BMI may not be an accurate measure of actual body fat. Other direct measures of body fat calculation may be required. Regardless of muscularity, a BMI of 25 is considered overweight, and a BMI over 30 is considered obese.

Other factors to consider include differences between males and females and the effects of aging. With the same BMI, females tend to actually have more body fat than males. Similarly, with the same BMI, the elderly tend to have more body fat than people who are younger.

These are 2 considerations to keep in mind when using BMI as a factor in determining your health. Physicians strongly recommend using BMI in coordination with waist circumference and the assessment of other health conditions to better determine your risk for disease and cancer.

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