The body mass index is a number calculated using your height and weight. BMI is commonly used as a screening tool to determine your possible risk for diseases, such as heart disease or diabetes. BMI is a fairly reliable indicator of fatness for most people and is an easy and inexpensive screening method. While no BMI number is considered perfect, falling into the normal range is most healthy.
BMI for Adults
The BMI range considered normal or healthy for adults is 18.5 to 24.9. Underweight BMI range is below 18.5 The two overweight categories that imply greater health risks include the BMI range of 25 to 29.9 or overweight, and obese, a BMI of 30 or greater. An example of the weight ranges at a height of 5-foot-9 would be as follows: underweight, 124 lbs. or less; normal, 125 to 168 lbs.; overweight, 169 to 202 lbs.; and obese, 203 lbs. or higher.
BMI and Body Fat
BMI doesn't calculate body fat but correlates closely with other body fat measures. There are differences between various groups when considering only BMI. For example, at the same BMI, women tend to have more body fat than men. Older adults will have a higher amount of fat than a younger person with the same BMI, and people with a high level of muscularity may have a high BMI without the typical corresponding level of body fat.
Fat vs. Muscle
While the BMI doesn't actually calculate the amount of fat and muscle, it gives most people a reliable idea if they carry too much fat for optimal health. Fat, unlike muscle, affects many body systems in a negative way contributing to many chronic diseases. People without much lean muscle mass can still have too much fat and score in the normal range of BMI, just as people with a great deal of muscle can fall into the overweight category. For a better reflection of actual body fat percent, various measures are available including underwater weighing and skinfold caliper tests.
BMI and Risk Factors
BMI is a screening method and only one of several factors to determine disease risk. According to the National Heart Lung and Blood Institute, additional factors associated with overweight and obesity that put you risk at for disease include larger waist circumference, high blood pressure, high LDL cholesterol, low HDL cholesterol, high triglycerides, elevated blood glucose, family history of premature heart disease, physical inactivity, and cigarette smoking.
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