What is Body Mass Index (BMI)?

Body Mass Index or BMI is a tool for indicating your body weight status. Your BMI correlates with your total body fat – if your BMI is high, you are most likely overweight or obese. It is important for you to know your BMI to help you understand if you are at risk for certain diseases. As BMI increases, the risk for some disease increases.

If your BMI indicates that you are overweight or obese, you may be at risk for:

* Cardiovascular disease
* High blood pressure
* Osteoarthritis
* Some cancers
* Diabetes
* Premature death

How do I determine my BMI?
BMI is determined by measuring your weight related to your height. The best way to find out your BMI is to use an online calculator that automatically calculates your BMI based on your weight and height. This online calculator at the Centers for Disease Control website will provide you with more information about what your BMI means.

What does my BMI score mean?
For adults over 20 years old, BMI falls into one of these categories:
BMI Weight Status
Below 18.5 Underweight
18.5 – 24.9 Normal
25.0 – 29.9 Overweight
30.0 and Above Obese

BMI for children and adolescents should not be calculated using the adult scale (see section below).

Remember, BMI is only one indicator. It does not mean that you will definitely developed a disease or that you are definitely overweight or obese. Two limitations to BMI are that BMI scores often overestimate body fat for those who are athletic or are very muscular, and they are often an underestimation of body fat for older adults or those with a loss of muscle mass.

Is BMI important for children?
In children and teens, BMI is used to assess underweight, overweight, and risk for overweight. (CDC) It is important to use a BMI scale for children because it takes into account a child’s gender and age, in addition to height and weight. Because children's body fatness changes over the years as they grow and because body fatness is different for boys and girls as they mature, these BMI-for-age calculators use gender-specific growth charts to determine a child’s BMI. The BMI score is reported as a percentile. (example: If your child is at the 70th percentile, that would mean that compared to children of the same age and gender, 70% have a lower BMI).

According to the Centers for Disease Control, healthcare professionals use the following established percentiles to identify underweight and overweight in children.
Underweight BMI-for-age < 5th percentile
At risk of overweight BMI-for-age 85th percentile to < 95th percentile
Overweight BMI-for-age > 95th percentile

How do I determine my child’s BMI?
To find out if your child is at risk for being overweight or underweight, go to this online BMI for Children calculator. Developed by the website What you Need to Know About Pediatrics, this age and gender-specific calculator for children ages 2-20 will provide you with additional information to help you better understand your child’s BMI. The calculator and feedback are intended for parental use – not for children to use by themselves.

Sources:

Centers for Disease Control
National Center for Chronic Disease Prevention and Health Promotion
Nutrition and Physical Activity
http://www.cdc.gov/nccdphp/dnpa/bmi/bmi-adult.htm