Health professionals use a variety of criteria to determine ideal weight. Body mass index (BMI) is one method of calculating one's ideal weight based on one's height. According to the Centers for Disease Control (CDC), BMI is easy to use, inexpensive, and a fairly reliable indicator of body fat content. A BMI above ideal range points to higher risk of chronic diseases. Losing excess weight has been shown to improve these health conditions.
Calculating BMI
To calculate BMI, first divide weight in pounds by height in inches squared, then multiply this figure by 703 to get the BMI. As an alternative, tables and BMI calculators are available from the National Heart Lung and Blood Institute (NHLBI) and other agencies. Charts are often available in physicians' offices. On charts, find height in inches along the left side, and weight in pounds across the top. The BMI number will be in the box where the height row and the weight column meet.
Correlating BMI to Weight
The healthy BMI range according to the NHLBI is between 18.5 and 24.9. This correlates to a range of weight based on the height of an individual. For example, for a person who is 5 feet 5 inches tall (65 inches), the ideal weight range is from 114 lbs. to 149 lbs.
High BMI and Health Risks
A BMI between 25 and 30 is considered "overweight" and above 30 is considered obese. The Center for Nutrition and Public Policy reports that health risks have been shown to increase as body fat increases. These risks include high blood pressure, diabetes, coronary heart disease and certain types of cancer. Obese people have a shorter life expectancy. Losing weight, with ideal BMI range as a goal, often helps to lower elevated blood sugar levels, blood cholesterol levels, blood pressure and subsequent risk of these chronic diseases.
BMI Interpretation
Some factors--such as age, gender, and fitness level--can affect body composition, but these are not reflected by BMI. For instance, as the CDC points out, women tend to have more body fat than men, and people who are older tend to have more body fat than younger people. BMI only takes height and weight into account, thereby missing some of these influences. A very muscular person can have the the same BMI as an obese person. In this case the more muscular person is not likely to be at risk for chronic disease as the BMI value alone suggests. Therefore, this test is used as a screening tool, with further assessments to be conducted as indicated by the health care team.
BMI as a Screening Tool
BMI and weight alone do not determine actual risk of developing chronic diseases. There are other factors to consider. The NHLBI encourages further medical evaluation if a person has a BMI of 30 or greater, or a BMI above 25 with two of the following risk factors: high blood pressure; high LDL cholesterol; low HDL cholesterol; high blood sugar; family history of early heart disease; physical inactivity; or cigarette smoking.
Member Comments