Anorexia, or anorexia nervosa, is characterized by an intense refusal to maintain a normal body weight-for-height. For adults, this usually means that the individual has a body mass index, or BMI, less than 18.5 or that the individual is less than 85 percent of ideal body weight. This condition puts the body at risk for additional medical complications and severely compromises quality of life.
Definition of Anorexia Nervosa
Anorexia nervosa is defined by the American Psychiatric Association as a medical condition whereby individuals do not maintain a normal body weight, fear gaining weight, experience body image disturbances, and, in females, miss three consecutive menstrual cycles. Anorexia is an often fatal condition, and many individuals who have anorexia often have other psychological and physiological problems.
Definition of Underweight by BMI
According to the World Health Organization, normal weight is considered to be a BMI of 18.5 to 24.99. A BMI of 17 to 18.49 is consider to be mild thinness, 16 to 16.99 is considered to be moderate thinness, and less than 16 is considered to be severe thinness. Because anorexia is defined as having a below normal body weight for height, a BMI below 18.5 would meet the criteria for anorexia.
Calculating Ideal Body Weight for Men
For males, ideal body weight is calculated as being 106 lbs. plus 6 lbs. for every 1 inch over 5 feet tall. For example, a man who is 5 feet, 9 inches tall should weight 106 lbs., plus 54 lbs., or 160 lbs. Because anorexia is defined as 85 percent or less of ideal body weight, this male would be considered anorexic if he weighed 136 lbs. or less.
Calculating Ideal Body Weight for Women
For females, ideal body weight is calculated as 100 lbs. plus 5 lbs. for every 1 inch over 5 feet tall. A female who is 5 feet, 1 inch tall would have an ideal body weight of 105 lbs. To meet the criteria for anorexia, she would need to be less than 89 lbs., which is less than 85 percent of her ideal body weight.
Child and Adolescent Populations
In children under the age of 18 years, BMI is calculated as a percentage-for-age, so when defining below normal weight-for-height in children, you will use the BMI percentiles. In children, a BMI percentile between the 5th and 85th percentile is normal. Any BMI percentile that is below than the 5th percentile is considered underweight, or less than normal, and meets the criteria for anorexia.
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