BMI Facts
BMI stands for body mass index and is a number that approximates a person's body fat. It is calculated with a formula that uses the person's height and weight. BMI does not measure actual body fat but is a quick, easy and inexpensive way to determine whether a person is normal, overweight or obese, according to the Centers for Disease Control and Prevention (CDC).
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Facts
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BMI is calculated in three basic steps. First, multiply your weight in pounds by 703. Second, convert your height to inches and square it. Third, divide the number from the first step by the number from the second step.
Formula: (weight in pounds x 703)/(height in inches)^2.
BMI can also be calculated using metric units, but requires a slightly different formula. For the metric formula, square your height in meters and divide it into your weight in kilograms.
Formula: (weight in kilograms)/(height in meters)^2
Significance
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A BMI of 20 to 24.9 is considered normal, 25 to 29.9 is overweight and 30 or above is obese, according to Discovery Health. People with a BMI of 25 or higher are at a higher risk for certain health conditions, including heart disease, stroke and high blood pressure, according to the CDC. For this reason, a physician may recommend a weight-loss program or may conduct more tests, such as waist measurement and an evaluation of risk factors for people with high BMIs. A BMI of less than 18.5 is considered underweight.
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Types
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The BMI formula is the same for men and women. For children and teenagers up to 20 years old, BMI is calculated the same way but interpreted differently. There are also separate interpretations for boys and girls, unlike the single interpretation for adults. A child's BMI is interpreted using a growth chart developed by the National Center for Health Statistics, which gives a BMI percentile. By CDC standards, a BMI in the 85th percentile means the child is at risk for becoming overweight, and a BMI in the 95th percentile means the child is overweight, according to Discovery Health.
Considerations
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Although BMI is a reliable estimation of body fat, it can be unreliable in certain situations. Muscle weighs more than fat, so people with a lot of muscle mass, such as athletes, have higher BMIs, sometimes into the overweight or obese range, even though they have little body fat. Older people tend to have less muscle mass and more body fat, so their BMIs could be too low for their actual body fat, according to the National Heart Lung and Blood Institute.
Solution
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People who are overweight or obese should lose weight. The National Heart Lung and Blood Institute recommends that overweight or obese patients start out with a goal of losing 10 percent of their weight at the rate of 1 to 2 lbs. each week, which means that patients should cut back their caloric intake by 500 to 1,000 calories per day according to the National Heart Lung and Blood Institute's Obesity Education Initiative.
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