As of 2008, about 1.5 billion adults aged 20 and older were overweight, according to the World Health Organization. About 500 million, or more than one in 10 of the world's population, were obese. The risk of developing certain chronic conditions rises as weight increases, so a screening tool such as the body mass index, or BMI, can help to identify those who may need to lose weight to improve their health.
Body Mass Index Calculations
A person's BMI -- body mass index -- is calculated from his height and weight to determine if he is overweight, obese or at a healthy weight. To determine your BMI, you can use an online calculator such as the one available on the National Heart Blood and Lung and Institute website, or you can perform the calculation manually. To perform the calculation manually, determine your weight in pounds and your height in inches. Divide your weight by the number that results from squaring your height and multiplying it by a factor of 703, according to the Centers for Disease Control and Prevention. The formula is "weight (lb) / [height (in)]2 x 703." For example, the BMI of a person who weighs 150 pounds and whose height is 65 in. is calculated by dividing 150 by ( 65 x 65) x 703, for a BMI of 24.96.
Interpreting Body Mass Index
To interpret the BMI for a person aged 20 or older, refer to a Body Mass Index chart. For men and women of any age, a person with a BMI less than 18.5 is underweight. Normal weight range is between 18.5 and 24.9; overweight is 25 to 29.9; and obesity is 30 or higher, according to the Centers for Disease Control and Prevention. While BMI does not measure fat directly, the figures correlate to more direct means of determining overweight and obesity.
Health Risks Related to BMI
People in the overweight and obese BMI ranges have a higher incidence of chronic diseases such as osteoarthritis, diabetes mellitus, stroke, high blood pressure, gallbladder disease, liver disease, heart disease, and some cancers. Although a high BMI is only one risk factor for developing these conditions, maintaining a healthy weight -- a BMI of 18.5 to 24.9 -- or losing weight can reduce these risks. Other factors that should be considered risk factors include age, gender, lifestyle, and family history.
Healthy BMI
In general, a BMI between 18.5 and 24.9 is the goal for most people. However, the BMI is a screening tool, not a direct measurement of body fat, so certain individuals may be healthy at a higher or lower BMI. Gender, for example, makes a difference since women have more body fat than men with the same body mass index. Body mass index calculations cannot differentiate between muscle and fat, so a heavily muscled person may be healthy at a higher BMI than might be expected. People under five feet tall, the elderly, and African-American or Hispanic-American women may also find that the BMI does not accurately reflect their risk of developing obesity-related medical conditions. Anyone concerned about being overweight should see a health care provider to determine their health risks.
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