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About BMI
Welcome to the BMI Health Channel by eMedTV. BMI (or body mass index) is an indirect measure of body fat in a person. Because the BMI calculation only requires two pieces of information -- height and weight -- it is an inexpensive and easy method used to screen for weight categories that may lead to health problems such as diabetes, stroke, and heart disease. Calculating BMI can help determine if a person is overweight or obese; BMI calculations are often used in conjunction with other measurements (such as waist circumference) to assess a person's weight.
Who Can Use BMI?
Anyone can use BMI to assess body fat. Body mass index is calculated the same way, regardless of age, gender, or ethnicity; however, the results for children and teens are interpreted differently than those for adults.
While BMI results correlate closely to direct measures of body fat in most people, body mass index may overestimate the level of body fat in athletes or people with muscular build. Likewise, BMI may underestimate body fat in older people and others who have lost muscle mass.
What Is the BMI Formula?
There are two versions of the BMI formula.
If you're using the metric system, the formula to determine BMI is:
Weight in kilograms divided by height in meters squared (weight (kg) / [height (m)2]).
Since height is commonly measured in centimeters, divide height in centimeters by 100 to obtain height in meters before you use the formula.
If you're using the English system of measurement, the BMI formula is:
Weight in pounds (lbs) divided by height in inches (in) squared and multiplied by a conversion factor of 703 (weight (lbs) / [height (in)2] x 703).
Body mass index may also be determined using a BMI chart or a special "BMI Calculator."
How Are BMI Results Interpreted?
For adults 20 years of age and older, a BMI of 18.5 to 24.9 is considered normal, 25 to 29.9 is considered overweight, and a BMI of 30 or higher is considered obese. A person with a BMI under 18.5 is considered underweight; one of the criteria for diagnosing anorexia is a BMI under 17.5.
For children and teens (people under the age of 20), the BMI number is plotted on the BMI-for-age growth charts (for either girls or boys) to obtain a percentile ranking. The percentile indicates the relative position of the child's BMI result among children of the same sex and age. A healthy weight ranges from the 5th to the 84th percentile.
What Are the Risks Associated With Being Overweight or Obese?
People who are overweight (defined as a BMI between 25.0 and 29.9) or obese (defined as a BMI greater than or equal to 30) are at increased risk for developing a number of medical conditions, including:
  • High blood pressure (hypertension)
  • Heart disease
  • Stroke
  • High cholesterol or other lipid disorders
  • Type 2 diabetes
  • Certain cancers
  • Sleep apnea
  • Osteoarthritis
  • Gallbladder disease
  • Fatty liver disease.
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