Body mass index (BMI) is a measure used to determine your health status in relation to body composition. This measure utilizes a formula that takes into account a person's height and weight. The formula is weight (in pounds) divided by height (in inches) squared multiplied by 703. This is a standard formula, used for men, women and children, though the interpretation is different for children. The correlation between BMI and body fatness is fairly strong, but varies by sex, race and age.
Weight Categories for Adults
The resulting number from the BMI equation is grouped into one of four categories that determine the individual's weight status. A result below 18.5 is considered underweight, a result falling between 18.5 and 24.9 is considered to be normal, a result falling between 25.0 and 29.9 is considered overweight, and any result 30 and above is considered obese.
BMI Widely Accepted
While BMI is not a measurement without peers, it is commonly used by several health organizations as a standard for determining healthy body composition. For example, the National Institutes of Health defines normal weight, overweight and obese according to BMI vs. traditional height and weight charts. The reasoning behind the common usage of BMI is that it is readily available with no special equipment needed.
Alternatives to BMI
BMI is not a perfect measurement for determining whether an individual is overweight. Those who are body builders and athletes are prone to being unusually muscular, and muscle tissue weighs more than fat tissue. This increase in weight could cause the BMI to be in the overweight category, while the individual is in no need of weight loss. Another group of exceptions is the elderly. It is more beneficial for an elderly person to have a BMI between 25 and 27 for overall good health. It is also noted that for those over the age of 65, a slightly higher BMI can aid in preventing osteoporosis.
BMI for Children
BMI is age and gender specific. Children between the ages of 2 and 20 are given a value from the same equation used for adults, but are compared with others of their same age and gender, generating a percentile value. A way to find a child's percentile is to compare their BMI with the CDC's BMI-for-age charts, which take into account gender and age. The weight status categories are as such: Underweight is any value less than the fifth percentile, healthy is any value between the fifth and the 85th percentile, overweight is any value between the 85th and 95th percentile and obese is any value above the 95th percentile. The percentile value is used to screen for possible weight problems and is not used as a diagnostic tool. The CDC and the American Academy of Pediatrics recommend that screening begin at the age of 2.
Conditions Tied to Abnormal BMI
For those individuals who do not fall into the normal category of BMI, there are associated health risks. Those who are overweight or obese are at risk of heart disease, sleep apnea, type 2 diabetes, osteoarthritis, stroke and some cancers. There are also associated risks with being underweight. A low BMI is a warning sign for anorexia. It is important to note that not all people who have a low BMI are anorexic. Some medical complications associated with anorexia include irregular heartbeat, heart attack, anemia and osteoporosis, and the condition can lead to death.
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