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Knowing Your Body: Body Mass vs. Body Fat—Should You be Concerned?

on March 5 | in Health & Fitness | by | with No Comments

Body Mass Index or Body Fat Percentage—No More Confusion

Your body composition is important.  Body Mass Index (BMI) and Body Fat Percentage (BFP) are two of the most talked about and two of the most misunderstood terms in health and fitness.  I hear the terms interchangeably.  It makes me cringe.  Body Fat Percentage is an important number to know and understand, especially for intense exercise and fitness enthusiasts.  Body Mass Index is not comparatively all that important, but it is important to understand how it is derived.  Let’s explore both BMI and BFP.

body mass index

Body Mass Index—What’s my number? How do I get it?  Does it matter?

Body Mass Index or BMI is a simple index formula based on height and weight.  The formula is as follows: (your weight x 703) ÷ (your height in inches, squared).  Scores are generally interpreted as follows.  Under 18.5 = underweight; above 30.0 = obese.  Normal = 18.5 to 24.9 and overweight = 25.0 to 29.9.

BMI is usually illustrated as a height and weight grid chart.  You can find a BMI grid chart hanging in almost every medical office.  Why? Because medical practitioners use the chart, when needed, to politely illustrate to a patient that they need to lose weight, or sometimes gain weight, to improve their health.

BMI is not particularly helpful or enlightening for most athletes or fitness types.  This is because the formula only uses two pieces of input data: height and weight.  If you work out regularly and are uber-active, you should not pay too much attention to your BMI.  I will use myself as an example to illustrate why BMI is not a good indicator of body composition.  Currently, my calculated BMI is 19.1.  The BMI chart suggests that my BMI is normal.  When I was playing college softball more than ten years ago and in the best shape of my life physically, my BMI was 22.6.  The BMI chart says normal, but a slight increase in weight, and I would have been nearing the overweight category.  How could this be? BMI does not take into account many important factors with regard to body composition, most notably lean muscle mass.  Many athletes register as overweight with regard to BMI.  It is important to remember that BMI tells only the average normal activity person in very general terms about whether or not they may be overweight or underweight.  BMI must be augmented with other, more specific tissue evaluations.  The better measure of body composition, especially for athletes and fitness types, is body fat percentage.

Body Fat Percentage—What’s my percentage? How do I get it?  Should I care?

Yes.  As an athlete or fitness type, you should care about your Body Fat Percentage, because BFT is one of the most valuable tracking numbers in terms of measuring health and fitness outcomes over time.  The number tells you what percentage of your body is made up of fat versus bone, muscle, and other tissue. Each person has an ideal fat percentage.

If you are not sure what your ideal body fat percentage is or should be, talk to your health care professional.  There are many ways to obtain one’s estimated body fat percentage.  Body composition analysis tools are not equal in terms of accuracy or costs.  Costs from method to method can vary widely.  The most common methods used today are the skin-fold caliper method, the Hydrostatic Body Composition test, the Bod Pod, and the newest addition, DXA Composition scanning.  Let’s explore each to see how they compare.

Skin-fold Caliper Method, $10-20

caliper to test body fat-healthThe skin-fold caliper method uses various skin-fold techniques to gather data and is generally considered the most accessible and cost-effective way.  Many use this method to chart general progress.  It should also be noted that calipers cannot be totally accurate as it is extremely difficult to be precise in terms of caliper body measurement location time after time.  Here are a few methods using calipers: Jackson/Pollock 7 Caliper Method, the Parrillo Caliper Method, and the Durnin/Womersley Caliper Method.  Each uses a different number of measurements from a variety of areas of the body to arrive at Body Fat Percentage.  Caliper methods can be time consuming, but also very inexpensive.  You can get a skin-fold caliper test at nearly any medical practitioner’s office.  You can even purchase your own set of calipers and have a trusted friend or family member take and record measurements for you.

Hydrostatic Body Composition Test, $45-65

The Hydrostatic Body Composition test is based on whole-body measurement principles. By obtaining your land weight and water weight (based on buoyancy), a specialized computer program can scientifically calculate your body fat as a percentage of your total weight. This principle is based on the fact that bone, muscle, and connective tissue collectively known as lean mass sinks, while body fat floats (hydro-densitometry).  This test takes under 15 minutes, and falls in the mid-range in terms of cost.  If you do not like water or being under water, however, this evaluation may not be for you.    

Bod Pod, $50

bod pod-health articleBased on whole-body measurement principles, the Bod Pod employs patented air displacement technology instead of a water dunk. The subject being measured sits comfortably inside the capsule while computerized pressure sensors determine the amount of air displaced by their body.  This test is said to be accurate, safe, and quick, with a complete analysis taking under 10 minutes.  If you are not comfortable in close spaces, this evaluation may not be for you.  The Bod Pod also falls in the mid-range in terms of cost.

DXA Body Composition Scanning, $80-120

DXA Body Composition Scanning is said to be the most accurate method of body composition analysis and seems to be the current gold standard for most research applications.  During a DXA, or dual-energy X-ray absorptiometry body scan, an arm passes over the bodyDXA provides the subject an illustrated analysis of their body, showing fat in yellow, muscle in red, and bone in blue.  DXA  gives detailed evaluations about specific regions of the body such as the chest, shoulders, or thighs so one can easily follow and monitor progress in specific areas.

body composition scannerThe DXA Body Composition does more than just analyze your body fat percentage, however.  DXA can also measure and differentiate actual weight in grams for specific muscles along with the fat within the muscle groups.  This is helpful for those looking to identify their gains or loss in muscle and fatty tissues in a specific muscle group or regions of the body. If you are looking to gain pure muscle mass in just your legs, therefore, DXA can measure the specific gains in that area. This type of information can be used to modify future workouts based on progress in those areas.

The scans take about 3 minutes each, and the DXA Body Composition analysis gives a greater volume of scientific data than its competitors, and many medical professionals believe it is the most accurate.  The drawback to DXA is that it is expensive compared to other methods.

There are other methods of measuring body fat percentage available; however, these four seem to be the most commonly used.  If you are looking to get your body fat percentage calculated, talk to your health care provider.  Using body fat percentage to track how well your workouts are meeting your goals is a very beneficial way to monitor progress and to plot a successful path forward.  To your health, onward!

Photo Credit: Bodycomp via Compfight
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