Body weight commonly indicates an individual's health. An individual's weight can be classified as healthy, underweight, over-weight or obese. A way to categorize a person's weight is by determining their BMI, or body mass index. BMI shows the relationship between a person's height and weight. BMI is used to diagnose those at risk for heart and health problems, depending on the category they fall in. Adult men and women can use the BMI scale, however for children and teens you must take their gender and age into consideration.
Calculating Your BMI
You can calculate your body mass index by using this formula: [weight (in pounds) / height (in inches) x height (in inches)] x 703. Or you can use an online calculator provided by the National Heart Lung and Blood Institute. Or, there are numerous online calculators available to calculate your BMI. For instance, the National Heart Lung and Blood Institute provides a calculator to aid in determining adult's BMI.
Purpose of BMI
The Centers for Disease Control and Prevention (CDC) uses BMI to calculate obesity and those overweight in the general public, which aids in identifying those at risk for coronary and other health conditions. The following is a means for interpreting BMI as provided by the CDC; individuals with a BMI under 18.5 are considered underweight, a BMI in the range of 18.5 to 24.9 indicates a normal healthy weight, a BMI of 25 to 29.9 identifies overweight individuals, and those with a BMI of 30 or greater are considered obese.
Misconceptions
BMI is not an accurate measure of body fat. The CDC reminds us "BMI is not a direct measure of body fatness and that BMI is calculated from an individual's weight which includes both muscle and fat." Muscle mass is not accounted for in a person's BMI. According to the BMI weight status categories, anyone with a BMI over 25 would be classified as overweight and anyone with a BMI over 30 would be classified as obese. Athletes with a BMI over 25, does not mean they are obese. Therefore, a more accurate measure of body fat would be needed.
Risks of a High BMI
The BMI categories are based purely on the relationship between body weight and height, and their correlation with disease and death. The CDC lists diseases and health risks for individuals overweight and obese including hypertension, dyslipidemia (for example, high LDL cholesterol, low HDL cholesterol, or high levels of triglycerides), Type 2 diabetes, coronary heart disease, stroke, gallbladder disease, osteoarthritis, sleep apnea and respiratory problems and some cancers (endometrial, breast and colon).
BMI in Children and Teens
BMI calculations are commonly done at yearly physical check-ups as a means of screening children for obesity, over weight, underweight and healthy weight. According to the CDC, BMI is calculated for children and teens the same way as it is for adults, however the interpretation of this number is different. Once the BMI is calculated, the number then gets plotted on a growth chart according to the child's age and gender. The plotted point on the chart determines a percentile. The percentile indicates the relative position of the child's BMI number among children of the same sex and age in the United States.
The CDC states that interpretation for children's and teen's BMI's are different than adults because, "the amount of body fat changes with age and the amount of body fat differs between girls and boys."
The U.S. Department of Health and Human Services provides an online calculator that takes into account children's gender and age when determining their BMI.
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