What is BM! ?

Body Mass Index or BMI is a tool for indicating weight status in adults. It is a measure of weight for height. For adults over 20 years old, BMI falls into one of these categories:

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BMI	Weight Status
Below 18.5	Underweight
18.5 - 24.9	Normal
25.0 - 29.9	Overweight
30.0 and Above	Obese

Note: BMI for Children and Teens is based on gender and age specific charts. See below.

BMI correlates with body fat. The relation between fatness and BMI differs with age and gender. For example,women are more likely to have a higher percent of body fat than men for the same BMI. On average, older people may have more body fat than younger adults with the same BMI.

For more information about overweight among adults, see Clinical Guidelines on the Identification, Evaluation, and treatment of Overweight and Obesity in Adults.Bethesda, MD: NHLBI, 1998.

How Does BMI Relate to Health?

The BMI ranges are based on the effect body weight has on disease and death. As BMI increases, the risk for some disease increases. Some common conditions related to overweight and obesity include:

• Premature death
• Cardiovascular disease
• Osteoarthritis
• Some cancers
• Diabetes

BMI is only one of many factors used to predict risk for disease. BMI cannot be used to tell a person if he/she has a disease such as diabetes or cancer. It is important to remember that weight is only one factor that is related to disease.

What Does This All Mean?

So you have calculated your BMI and found which weight category your BMI matches. What does this all mean?

BMI is Not the Only Indicator of Health Risk.

BMI is just one of many factors related to developing a chronic disease (such as heart disease, cancer, or diabetes). Other factors that may be important to look at when assessing your risk for chronic disease include:

• Diet
• Physical activity
• Waist circumference
• Blood pressure
• Blood sugar level
• Cholesterol level
• Family history of disease

All persons who are obese or overweight should try not to gain additional weight. In addition, those who are obese or who are overweight with other risk factors should consider losing weight. A complete health assessment by a physician is the best way to decide the right steps for you.

Whatever your BMI, talk to your doctor to see if you are at an increased risk for disease and if you should lose weight. Even a small weight loss (just 10% of your current weight) may help to lower the risk of disease.

Physical activity and good nutrition are key factors in leading a healthy lifestyle and reducing risk for disease.

Common Myths

Myth: BMI Measures Body Fat

Two people can have the same BMI, but a different percent body fat. A bodybuilder with a large muscle mass and a low percent body fat may have the same BMI as a person who has more body fat because BMI is calculated using weight and height only.

These men have the same height, weight, and BMI, but may have different percent body fat.

6'3" Height 6'3" 27.5 BMI 27.5 220lbs Weight 220lbs

This is a good reminder that BMI is only one piece of a person's health profile. It is important to talk with your doctor about other measures and risk factors. (e.g., waist circumference, smoking, physical activity level, and diet.)

Myth: BMI is a Diagnostic Tool

BMI alone is not diagnostic. It is one of many risk factors for disease and death. As a person's BMI increases the risk for many diseases increases as well.

BMI for Children and Teens
(Also referred to as BMI-for-age)

BMI is Used Differently with Children Than it is With Adults

In children and teens, body mass index is used to assess underweight, overweight, and risk for overweight. Children's body fatness changes over the years as they grow. Also, girls and boys differ in their body fatness as they mature. This is why BMI for children, also referred to as BMI-for-age, is gender and age specific. BMI-for-age is plotted on gender specific growth charts. These charts are used for children and teens 2 – 20 years of age. For the 2000 CDC Growth Charts and Additional Information visit CDC's National Center for Health Statistics.

Each of the CDC BMI-for-age gender specific charts contains a series of curved lines indicating specific percentiles. Healthcare professionals use the following established percentile cut-off points to identify underweight and overweight in children.

Underweight	BMI-for-age <>
At risk of overweight	BMI-for-age 85th percentile to <>
Overweight	BMI-for-age <>
What does it mean if my child is in the 60th percentile? The 60th percentile means that compared to children of the same gender and age, 60% have a lower BMI.	BMI decreases during the preschool years, then increases into adulthood. The percentile curves show this pattern of growth.

Example

Let's look at the BMI for a boy as he grows. While his BMI changes, he remains at the 95th percentile BMI-for-age.

Age	BMI	Percentile
2 years	19.3	95th
4 years	17.8	95th
9 years	21.0	95th
12 years	25.1	95th

We see how the boy's BMI declines during his preschool years and increases as he gets older.

Why is BMI-For-Age a useful tool?

BMI-for-age is used for children and teens because of their rate of growth and development. It is a useful tool because

• BMI-for-age provides a reference for adolescents that can be used beyond puberty.
• BMI-for-age in children and adolescents compares well to laboratory measures of body fat.
• BMI-for-age can be used to track body size throughout life.