Body mass index (BMI) is a tool for evaluating a person's weight based on their height. Based on the BMI, a patient can be determined to have normal weight, to be underweight, overweight, or obese. For adults over 20 years old, a BMI of <18.5 is underweight, 18.5-24.9 is normal, 25.0-29.9 is overweight, and =30.0 is obese. BMI for children is different than BMI for adults and is plotted on gender specific growth charts. This document focuses on adult BMI.
BMI alone is not an absolute diagnostic tool. However, BMI that is too high or too low is associated with a greater risk of developing chronic diseases.
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Body mass index (BMI) is a widely accepted measurement that has been correlated with risk of developing certain diseases.
For example, being overweight or obese increases the risk of health conditions, such as stroke, cardiovascular disease, hypertension, type 2 diabetes, dyslipidemia, osteoarthritis, respiratory problems, and cancer. On the other hand, being underweight on the BMI scale may increase the risk of amenorrhea, bone loss, malnutrition or other conditions.
Additionally, although BMI correlates with body fat, it does not accurately measure body fat. For example, women are more likely to have a higher percent of body fat than men with the same BMI. Also, usually, older people have more body fat than younger adults with the same BMI. Finally, a BMI calculation may overestimate body fat in athletes and others with a muscular build.