Corporate wellness program members hear terms like BMI, body fat percentage, girth measurements, and waist-to-hip ratio floating around on a daily basis. There is more to a person's body composition than just the number on the scale, but what number matters the most? Let's compare body mass index (BMI) to body fat percentage.
Using BMI (Body Mass Index) to Measure Employee Health
BMI is a ratio of a person's height to weight. Think of it as a chart where you would find your height on one side and your weight on the other. Connect the two dots, and boom: That number you landed on is your BMI. (Here's an online BMI calculator.)
As you can see just from that description, BMI is a very general assessment of overall body makeup. It tends to be more abstract. Tell someone that his or her BMI is 23.7 and, chances are, that won't mean much to the individual. People are classified as either underweight, normal, overweight, or obese, with no breakdown within those broad categories.
Body Fat Percentage for Determining Employee Health
Percent body fat, on the other hand, requires a more involved process for testing (including bioelectric impedance, skinfolds, underwater weighing and BodPod (air displacement) technology) to determine how much of a person's total body weight is comprised of fat versus fat-free mass (muscles, bones, organs, tissue, etc.). Body fat percentage is more telling of a person's fitness level. Two people may look the same as far as appearances go, and quite possibly have the same BMI. But they could have very different body fat amounts.
The application of percent body fat is simple. If a person weighs 160 pounds and is told his body fat is 15%, he can do the math and know that he is carrying 24 pounds of fat and 136 pounds of fat-free mass. If this person loses 10 pounds over the course of a few months and retests his percent body fat, he will have specific data to compare, whereas his BMI rating may be in the same category as it was before.
Why Percent Body Fat Is a Better Emloyee Heath Measurement
Over the years I have seen articles surface claiming things such as that BMI may not be an accurate measurement for different ethnicities, neck measurements are just as valid as BMI, etc. But percent body fat cannot be as easily argued against.
The big commonly known fault with BMI, and the reason behind its generality, is that the number does not take muscle mass into account. This makes BMI misleading in two ways:
- Firstly, a person who is underweight or normal on the BMI scale may still have a high percentage of body fat, meaning a lower level of fitness.
- On the flip side, a person with a large amount of muscle mass, for example a football player or bodybuilder, could be told by the BMI ranking that he or she is morbidly overweight, when the individual in fact has a low percent body fat and high fitness level.
I perform body composition tests in my corporate fitness center, using the Jackson-Pollock 7-site skinfold protocol, and I see these scenarios often. I have to explain the huge discrepancy when a person's BMI is in a healthy range but the body fat percentage is high, or vice versa.
The bottom line is that BMI is a general overview and can be an introductory assessment of a person's body composition. It's perhaps useful when more involved testing is not available. For more truth behind the matter, look at percent body fat.
(Further reading: See this article, which discusses the validity of both numbers.)