How Accurate Are Bmi Scales?

The body mass index scale is used by many health care professionals as a means to quickly assess a person's weight. The objective of the BMI scale is to predict your percent body fat. Knowing your percent of body fat can help you determine the risk of chronic disease and whether any lifestyle changes should be done to help control weight gain. However, the BMI scale may not be the most accurate means of determining body fat.

The BMI Scale

When you determine your BMI, you are given a score. If your score is under 18.5 you may be considered underweight. From 19 to 24.9 is normal, 25 to 29.9 is overweight and 30 and above is obese.

Accuracy

The use of the body mass index scale for diagnosing obesity may be unreliable, according to a study published in the "International Journal of Obesity" in 2008. This study took 13,601 participants ages 20 to 79.9, and compared body fat percentage taken by bioelectrical impedance with BMI. The BMI scale failed to correctly estimate body fat in many of the individuals with a score of 25 to 29.9, severely underestimating percent body fat.

Age and Gender

Since the BMI only takes into account height and weight, it fails to recognize two prospective influences on body fat: age and gender. Older people and females tend to have a larger percentage of body fat. It is because of this that the BMI scale may not be able to accurately diagnose an individual as obese, even when the body fat percentage would indicate them as such.

Body Composition

Another limitation is the actual body composition of the individual. Let's say you are a top athlete in your sport. Chances are your body fat percentage is pretty low and your lean body mass impressive. The BMI scale only knows your weight and not that you train for your sport for hours a day. Since your lean body mass contributes to your weight, you would still be classified as overweight or even obese. The same holds true for individuals with short legs. Since height and weight is only accounted for, people who have shorter legs may be classified as overweight even when they are not.

Usefulness

The BMI scale does have its usefulness. It is the most inexpensive and easiest way to estimate if your weight is healthy or unhealthy. It can be used as a screening tool for further weight assessment. It can also be used as a motivator or tracker for those who are overweight or obese. The Centers for Disease Control states that BMI is useful for most populations and may be a passable indicator of body fat.