Body Mass Index   

The BMI is a measure of your weight relative to your height and waist circumference measures abdominal fat. Combining these with information about your additional risk factors yields your risk for developing obesity-associated diseases.
  

The Federal guidelines on the identification, evaluation, and treatment of overweight and obesity in adults released by the National Heart, Lung, and Blood Institute (NHLBI), in cooperation with the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) defined "overweight" as a body mass index value between 25 and 29.9; and "obesity" as a body mass index value greater than or equal to 30. 

Body Mass Index (BMI) is a reliable indicator of total body fat, which is related to the risk of disease and death. The score you get is valid for both men and women over age 18 with the following exceptions: 

It may overestimate body fat in athletes and others who have a muscular build. 

It may underestimate body fat in older persons and others who have lost muscle mass.  

BMI is useful because it is easy to calculate, but it is not a particularly accurate measure because it does not differentiate muscle mass from fat mass.  

BMI can only be used to determine body fat in adults. In children, it is more appropriate to use growth charts to measure the gain in height and weight. 

If your BMI is below 18.5 

Underweight individuals have increased risk for respiratory disease, tuberculosis, digestive disease and some cancers 

If your BMI is below 20 

This indicates a lean BMI, which means you have a low amount of body fat. If you are an athlete, this can be desirable. If you are not an athlete, a lean BMI can indicate that your weight may be too low which may lower your immunity.  

If your BMI and body weight are low, you should consider gaining weight through good diet and exercise habits, to increase your muscle mass.  

If your BMI is between 20 and 22 

This indicates the ideal, healthy amount of body fat, which is associated with living longest, and the lowest incidence of serious illness.  

Coincidentally, it seems this ratio is what many individuals perceive to be the most aesthetically attractive. 
 

If your BMI is between 22 and 25  

This is still considered an acceptable range, and is associated with good health. 

If your BMI is between 25 and 30 

You are considered “Hefty” and should finds ways to lower your weight, through diet and exercise. You are at increased risk for a variety of illnesses at your present weight. You should lose weight by changing your diet and exercising more. 

If your BMI is over 30 

This indicates an unhealthy condition, your excess “Prosperity” is putting you at risk for heart disease, diabetes, high blood pressure, gall bladder disease and some cancers. You should lose weight by changing your diet and exercising more.