Over 100 million adult Americans are overweight or obese. Being overweight or obese increases a person's chances for developing many diseases, especially
heart disease,
stroke,
diabetes, and cancer. How can someone determine if he or she is overweight or obese? Research on obesity has shown that a calculation called body mass index (or
BMI for short) can be used to measure body fatness.
Body mass index does not measure body fat directly, but it corresponds closely to direct measures of body fat. Therefore, body mass index can be considered an alternative for direct measures of body fat.
Body mass index is determined using a person's height and weight. Because the BMI calculation requires only these two simple pieces of information, it is an inexpensive and easy-to-use method of screening for weight categories that may lead to health problems
(see Health Effects of Obesity).
How Is Body Mass Index Calculated?
- Use the BMI formula
- Use the BMI chart
- Use the BMI calculator.
Any of these three methods will get the same body mass index result. Everyone can use one of these three methods, regardless of age, gender, race, or ethnicity. There is no specific BMI chart for women or men.
Interpreting Body Mass Index Numbers
Once the body mass index number is determined, it can be interpreted for adults using standard weight status categories that are the same for both men and women. The standard weight status categories associated with body mass index ranges for adults are shown below:
|
BMI
|
Weight Status
|
|
Below 18.5
|
Underweight
|
|
18.5 – 24.9
|
Normal
|
|
25.0 – 29.9
|
Overweight
|
|
30.0 and Above
|
Obese
|
One criteria used to diagnose
anorexia is a
BMI under 17.5.
For children and teens, after determining the body mass index, the BMI number is plotted on the BMI-for-age growth charts (for either girls or boys) to obtain a percentile ranking. The percentile indicates the relative position of the child's BMI number among children of the same sex and age.
BMI-for-age weight status categories and the corresponding percentiles are shown in the following table.
|
Weight Status Category
|
Percentile Range
|
|
Underweight
|
Less than the 5th percentile
|
|
Healthy weight
|
5th percentile up to the 84th percentile
|
|
At risk of overweight
|
85th to less than the 95th percentile
|
|
Overweight
|
Equal to or greater than the 95th percentile
|
Body Mass Index and Weight
If someone has a high body mass index, does that mean that they are overweight or obese? Are they at increased risk for health problems? The answers to these questions depend on other factors.
Body mass index is just one factor to consider when assessing a person's weight. To determine if excess weight is a health risk, a healthcare provider will perform further assessments. According to recent guidelines, assessment of weight involves using three key measures:
- Body mass index
- Waist circumference
- Risk factors for diseases and conditions associated with obesity.
Keep in mind that body mass index is a screening tool; it is not used to diagnose any medical conditions but instead is used as one measure to assess a person's weight and his or her risk for developing certain medical conditions.
High Body Mass Index and Weight-Related Health Problems
If a person is overweight or obese, he or she is at an increased risk for certain medical conditions, including:
Even a small weight loss (just 5 to 10 percent of a person's current weight) will help to lower the risk of developing those diseases.
(Click BMI and Weight for more information on assessing your risk for obesity-related medical problems.)
Body Mass Index Versus Other Ways to Measure Body Fatness
The body mass index score is valid for both men and women, but it does have some limits. Body mass index may:
- Overestimate body fat in athletes and others who have a muscular build.
- Underestimate body fat in older people and others who have lost muscle mass.
In addition to body mass index, there are a number of different ways to measure body fatness. These other methods include:
- Skinfold thickness measurements (with calipers)
- Underwater weighing
- Bioelectrical impedance
- Dual-energy x-ray absorptiometry (DXA)
- Computerized tomography.
These other methods of measuring body fatness are more accurate than body mass index. However, these methods are not always readily available, and they are either expensive or require highly trained personnel.
How Many Americans Have a Healthy Body Mass Index?
Nearly two-thirds of adults in the United States are overweight (defined as having a
BMI equal to or greater than 25). This means that about 130 million adults weigh more than they should. Nearly 61 million adults are obese (defined as a BMI greater than or equal to 30).
Even more concerning is that approximately 15 percent of children and adolescents are overweight, and another 15 percent are at risk for being overweight (BMI-for-age between the 85th and 95th percentile). Child obesity is a growing problem. An alarming number of children are obese and developing diseases normally seen in adulthood.
Less than half of US adults have a
healthy BMI. This is equivalent to about 68 million adults. About 37 million women between the ages of 20 and 74 have an ideal body mass index. About 31 million men between the ages of 20 and 74 have an ideal body mass index.
Add this article to your Favorites
Email this article
Print