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Body Mass Index (BMI) 101

September 18th, 2012 · No Comments ·

Body Mass Index (BMI) (some call it Quetelet Index) is a statical measure of the weight of a person scaled according to height. BMI is used by many physicians and researchers studying obesity. It is the common benchmark of healthy weight for adults.

BMI is calculated with the formula using a person’s weight and height:


BMI = weight (in kg) divided by height (in m)2


Once you have the number, here is the explanation, but only for adults over 20 to 60 years old:

  • BMI less than 18.5 – People in the underweight category are naturally lean. If you have been restricting your diet, you should aim to gain weight and get back into the normal weight range for your height. It may indicate malnutrition, eating disorder or other health problems
  • BMI 18.5 – 24.9 – Well done, buddy. You are in the normal category. Try to maintain your weight through a combination of healthy diet and physical activity.
  • Overweight BMI – 25 – 29.9 – You should not gaining any more weight. Try to cut down on sugary and fatty foods and on the amount you eat to get back into the normal weight range for your height. Increasing your levels of physical activity will help. If you do not do anything, you have high risk of developing health complications like heart disease, diabetes, and osteoarthritis.
  • Obese – BMI 30 – 40 – If your body mass index is within this zone, your risk of health problems is high. It is important that you try to lose some weight.
  • Extremely Obese – BMI over 40.


The above is a just basic guideline for 80 percent of the people out there. BMI does have its limit. In other words, BMI may not be applicable for everybody.

  • BMI does not differentiate between muscle and fat. Because muscle is denser than fat, most professional athletes and bodybuilders are considered to be “overweight” or “obese” according to the BMI. For example, Lance Armstrong was classified as “overweight” when he competed in the 1993 Tour de France if BMI was used. (Lance Armstrong is American professional road racing cyclist. He won the Tour de France seven consecutive times, from 1999 to 2005.)
  • For children, differences in bone density are obvious. So, in the proportion of bone to total weight can mean the number at which these people are considered underweight. Therefore, you should not use BMI for children.
  • If you are 60 years old and above, your BMI may not be accurate too because your bones may begin to weigh less as you get older.
  • It also does not apply to pregnant lady.


Due to these limitations, body composition for athletes and bodybuilders would not be calculated using the body mass index. If it is used, a body builder may considered to be overweight. Instead, the body fat is normally preferred. In all cases, methods for actually measuring body fat percentage are always preferable to BMI for measuring healthy body size.

Bear in mind that BMI is only one of many factors used to predict risk for disease. It is not a diagnostic tool, just a rough screening tool. BMI alone definitely cannot be used to tell a person if he has a disease such as diabetes or cancer. While BMI does not give the full picture of a person’s health, it does give some basic information about a person’s health condition. Whatever number it is, focus on your overall health, fitness level, dietary variety, and self-satisfaction. Your well-being is certainly much more than just an absolute number.



Category: Other Fitness/Sports Articles

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