Health Options Alan Titchenal  & Joannie Dobbs                   Wednesday, August 19, 1998

BMI useful but physical still necessary

One of the simplest measures of a person's health risk factors is body fat. Being overweight or obese raises the risk of serious health conditions arising from hyper­tension, type 2 diabetes, coronary heart disease, stroke, osteoarthritis, respiratory problems and a number of cancers. Statistics show that there is an increased mortality due to all causes associated with heavier body weight in individuals.

It is currently estimated that more than 97 million adults in the United States are overweight or obese. Health professionals are always looking for better tools to measure and predict changes in body composition. Preventing a person from becoming overweight is simpler than helping a person to lose the weight, especially if a great deal of weight has to be lost.

For many years, height-weight tables were used to help predict “healthy” body weights. As tech­niques and equipment became more sophisticated, estimating the percentage of body fat became a more common standard of measure­ment. However, when you go for your physical, you may be told your Body Mass Index.

BMI has been defined as a new standard of measurement to deter­mine whether your body weight and body composition meets “healthy” guidelines to decrease disease risk factors.

BMI describes the relative weight for height of a person and is significantly correlated with a person's body fat. To calculate BMI, first square your height in inches. Next, divide your weight in pounds by the square of your height. Multiply the resulting figure by 704.5.

A BMI which is less than 18.5 is considered underweight; be­tween 18.5-24.9 is considered normal; 25-29.9 is considered overweight; and 30 and above is considered obese.

The BMI system is not perfect and here are a few important problems you need to understand about the BMI system.

1. The high end of the normal BMI range is approximately the high end of the height-weight table. So for example, if you are a 5-foot-3-inch female weighing 140 pounds, your BMI is 24.9. For people who are genetically small, this BMI calculation may indicate that they are normal, but they may have more body fat than is healthy for them.

2. BMI calculations for tall people generally underestimate the amount of body fat that they have and therefore may underestimate the amount of risk they have.

3. For a person who is heavy, but whose body composition is primarily muscle (Like a weight lifter), the calculated BMI may indicate that the individual is overweight or obese when they have low levels of body fat.

4. Excess fat in the abdominal area indicates increased disease risk regardless of body weight and may be overlooked.

5. Whenever a technique or theory has been developed using information based on statistics from large groups of people, the application to individuals may or may not be realistic.

Identifying if your BMI is accurate generally involves looking in a mirror and being brutally honest with yourself. Anyone with too much body fat can be at an increased risk for disease and death, no matter what the scale or BMI reflects. Identifying absolute risk status involves much more than calculating a BMI. It includes an evaluation of risk factors related to heart disease such as high blood cholesterol, smoking and physical inactivity, and a look at family history and factors related to diseases such as diabetes, osteoarthritis, and cancer.

It is important to understand that BMI was developed as a research tool. Though BMI is now being used in clinical settings and fitness clubs, it is no replacement for a good physical examination.