Body Mass Index (BMI) is the preferred method of measurement for doctors and researchers studying obesity. The formula used to calculate an individual's BMI is weight (in kilograms) divided by height (in meters) squared. There are also differences in the interpretation of the BMI score of children as they grow. Typically, the BMI will decrease in preschoolers and increase in adults. With children, the chart shows the percentile for the age of the child. For example, if a boy who is 2 years of age has a BMI of 19.3, he is in the 95th percentile for his age, meaning that 95 percent of children have a lower BMI score than he does.
BMI measurement is an efficient way to measure weight status as compared to the rest of the population, and is used to predict the risk for weight-related health problems. Although it is correlated with body fat, its implications differ according to age and sex. Women generally have more body fat than men, for example. Furthermore, a muscular athlete and an out-of-shape person can have the same BMI score. Older people tend to have more body fat than younger adults with the same BMI. Interpretation of the BMI scores, therefore, is not an exact science.
How is BMI related to overall health? The BMI rates show the effect that greater body weight has on increased risk for: cardiovascular disease, high blood pressure, diabetes, osteoarthritis, certain cancers, and ultimately, premature death. In adults over 20 years of age, the BMI chart shows BMI scores of less than 18.5 as underweight, while the normal range should be between 18.5 and 24.9. Those with scores falling between 25.0 and 29.9 are deemed overweight, while those at 30.0 and above are classified as obese. Another measurement used to assess health risks is waist measurement. When coupled with the BMI chart score, women with waist measurements of greater than 35 inches, and men with greater than 40 inches in circumference, are considered to be at even greater risk for health problems than those with lower waist measurements - even if their BMI scores are merely in the overweight as opposed to the obese range. It is important to note that BMI is only one indicator of relative health or risk for disease. With weight control and exercise, BMI scores can be brought into the healthy range, and overall health can be considerably improved.
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