Although there are different definitions of what a “normal” weight is, BMI, or Body Mass Index, is commonly used as an assessment tool to help determine if body weight is in a healthy range. BMI is fairly accurate in most cases; however, there are certain population groups in which using BMI may not be accurate. Ideal body weight is generally the weight at which an individual looks and feels their best.
BMI
BMI is a number that helps measure body weight in relation to height. BMI provides a good estimate of body fat percentage, helps determine if body weight is in a healthy range and establishes an individual’s risk for developing chronic diseases. BMI is a tool commonly used by the Centers for Disease Control and Prevention (CDC), the American Dietetic Association and the National Institutes of Health.
Calculating BMI
According to the American Dietetic Association, BMI can be calculated using the following formula: (weight in pounds X 703) / height in inches / height in inches. A person who is 5’8” tall weighing 200 Ibs. would calculate their BMI in the following way: (200 Ibs. X 703) / 68 inches / 68 inches = BMI 30.4.
BMI Calculators
The American Dietetic Association and CDC websites both provide adult BMI calculators that can quickly and easily calculate BMI. The CDC website also contains a child and teen BMI calculator.
BMI Categories
BMI weight categories include underweight, normal or healthy weight, overweight and obese. According to the CDC, BMIs of less than 18.5 are considered underweight, 18.5 to 24.9 a normal or healthy weight, 25 to 29.9 overweight and 30 or above obese.
Disadvantages of BMI
Although BMI is widely used to assess body weight, it does have some disadvantages. BMI does not account for age, gender or body composition. For example, individuals who have a high percentage of muscle mass could fall into an obese BMI category but may have a very low percentage of body fat. In the elderly, BMIs will often underestimate body fat due to a decrease in lean body tissue.
Other Methods
Waist circumference, waist-to-hip ratio and formulas for calculating ideal body weight are other ways to help determine normal, healthy weight ranges. According to the CDC, waist circumferences of greater than 40 inches in men and 35 inches in women increase the risk for developing chronic diseases. Waist-to-hip ratios measuring below .8 in women and below .9 in men are considered healthy measurements, according to AIDS InfoNet.
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