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Know Your BMI

Fitday Editor

When I first learned of BMI, or body mass index, in school, I never realized how frequently I would use the number. Friends and colleagues frequently ask me questions related to weight, and I always tell them to calculate their own BMI first because if they do make changes in the future, they will be able to determine their own progress.

BMI is a fancy way of determining if your height is proportional to your weight. According to the Centers for Disease Control and Prevention (CDC), BMI is an easy quantifiable way of measuring your body fat. The formula for calculating your BMI is:

Formula: weight (kg) / [height (m)]2


Formula: weight (lb) / [height (in)]2 x 703
Once your BMI is calculated, you can visit the CDC or World Health Organization (WHO) websites to determine which general weight category you fall into: underweight, normal, overweight, or obese. People who fall into the overweight or obese categories tend to have a higher risk for health problems, including diabetes and cardiovascular disease. BMI is widely used for people of all ages because it is a simple and inexpensive way to determine potential health and weight problems within a population.

However, BMI does have its critics due to its inability to determine proportion of fat to muscle, water, or frame size. While these are important factors, a BMI is still a good number to know and I recommend its use to my patients because it can easily be calculated from a calculator or website.

Basically, if you were on the lower end of the BMI range and wanted to make your number higher so you are closer to normal, you would probably want to increase intake of calories and fat. If you were in the higher range (i.e. overweight or obese), then you may want to decrease intake of calories and fat in order to lower your number and decrease your health risks.

I calculate my BMI every so often just to determine where my weight is in relation to the rest of the country. However, I always keep in mind that if my BMI changes, there could be other factors not related to body fat, such as muscle mass or water weight.

BMI can also be calculated for children. The formula is the same, but the number is plotted on a graph to determine which percentage a child falls in. The CDC has pre-set guidelines for BMI in children that look at the number in relation to age and gender. If your child falls between the 5th and 85th percentile, he/she is considered normal weight. Any number below the 5th percentile is underweight, above the 85th but less than the 95th percentile is considered overweight, and a BMI above the 95th percentile is obese.

BMI is a good indicator of body fat and can easily be calculated as long as your current height and weight is known. Additionally, most physicians use it to help determine if you are within a normal weight range or at an increased risk for obesity-related health problems. So calculate your BMI today and see if you want to change it!

Rhea Li is a Registered Dietitian who received her Bachelor's degree in Nutrition and Master's degree in Public Health from the University of Texas. She has a special interest in working with children and has received her certification in pediatric weight management. Currently, she is working on a research study to determine the importance of nutrition in pediatric cancer patients. In the past, she has worked with pregnant women and their children. In her spare time, she enjoys being with family, exercising, traveling and of course, eating.

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