Every time I visit my family doctor he prints out a clinical report for me and right at the top with all of my other vitals (pulse, blood pressure, age, height, weight), it lists my BMI. It’s a not-so-friendly little reminder that my BMI always teeters right at the edge of “normal” and “overweight” despite the fact that my doctor tells me I’m in tip-top shape. It always makes me think about the relevancy of a person’s BMI, and how that little number can discourage or encourage someone by a matter of one-tenth. So what does this number really mean?
BMI, or body mass index, is a number calculated by a person’s height and weight that is used universally to indicate body fatness. This number is often used to identify if a person may have an unhealthy amount of fat in their body, and are therefore overweight or obese. It is free and easy to calculate, which makes it a great tool for those who are not interested in more expensive, high-tech processes to calculate body fat.
If you want to calculate your own BMI, divide your weight in kilograms by your height in meters squared. For example, a person who is 5′ 6″ (167 centimeters – 1.67 meters) and weighs 150 pounds (67.5 kilograms) would have a BMI of 24.2. If math isn’t your forte, Centers for Disease Control and Prevention website has a calculator:
Once you calculate your BMI you would see where you fall in the following categories:
Below 18.5 – Underweight
18.5-24.9 – Normal
25.0 – 29.9 – Overweight
30.0 and above – Obese
So, say you’re like me and your BMI falls between 24.8 and 25.2 depending on the day. Does that mean you have an unhealthy amount of body fat one day and the next you’re in the clear? Not necessarily. BMI is not fool-proof. It is meant to be used as an indicator for unhealthy weight, but it is not a tell-all. It doesn’t take age, sex, race, or muscular structure into account, all of which can alter the ranges above. If you’re a body builder your BMI is most likely going to be way higher than normal, even though you probably have a very low amount of body fat.
This is why National Heart, Lung, and Blood Institute recommends looking at two other indicators (waist circumference and other risk factors such as high blood pressure or sedentary lifestyle) to determine whether the issue is really body fat or other factors that are causing a high calculated BMI.
Consult with your physician regarding your BMI. Like in my case, my doctor knows that I am very active and have few risk factors for heart disease. Therefore, my teeter-totter BMI is not very concerning – even though it might be frustrating!