Body Fat Percentage Or Body Mass Index? Making Sense Of It All

Most of us use the scale to determine how much progress we  make toward better health and fitness; however body composition is one of the most important indicators for general health. The most commonly used measurement of body composition is Body Mass Index (BMI). While there are many ways to measure body composition, there are also many factors that determine body composition which can make for a complicated understanding.

Throughout the health and fitness world, using BMI measurements to determine weight classification has received a lot of criticism because it does not account for body fat composition. Because muscle tissue weighs more than fatty tissue, a person with high muscle mass might receive a misleading classification using the BMI system. For example, Adrian Peterson—running back for the Minnesota Vikings—was recently named the NFL’s Most Valuable Player award and has been renowned for his fitness, but his 28.6 BMI classifies him as borderline obese.

BMI is established by measuring your body weight in kilograms (1kg = 2.2lbs) and dividing it by the square of your height in meters (1m = 3.28ft).

The final equation reads:
BMI = Body Weight (kg) / Height2 (m2)

The resulting number determines your classification:

·    Underweight (<18.5),
·    Optimal weight (18.5 – 25),
·    Overweight (25.1 – 30), or
·    Obese (30.5+).

Many physicians use BMI measurements to obtain a general status of your weight, however it can be inaccurate.  There are also many tools online that will calculate your BMI for you.  Check out http://nhlbisupport.com/bmi/bminojs.htm.

Over the last 20 years an overwhelming amount of peer-reviewed studies have been published showing strong correlations between your BMI and your risk for cardiovascular disease, diabetes, stroke, and even osteoarthritis. The main advantage to using BMI is that it is very easy to calculate and it requires no expensive equipment; however its biggest critique comes from its lack of specificity.

A more accurate determinant for assessing your body composition is by measuring your body fat percentage.  There are currently four accepted methods for determining body fat percentage, or how much of a person’s weight comes from fatty tissue.

Dual-Energy X-Ray Absorptiometry (DEXA)- This is the most accurate measure as it measures bone density, fat mass, and muscle mass, but it requires expensive equipment and lengthy training.  Some of these machines were created for obesity research and to help discover deep belly fat, and unfortunately the test generally ranges from $59 to $399.

Skin-fold assessments- This measures the thickness of skin folds at specific anatomical locations but allows for large margins of error. This measurement can be performed at most any local gym by a personal trainer and is normally included in the cost of your sessions.  The more skilled trainer can determine a more accurate measurement and it is easy to access.

Hydrostatic Weighing is a form of measuring body fat composition and is usually found in higher-level athletic settings and takes advantage of fatty tissue’s buoyant properties and compares your weight when you are on dry land with your weight completely submerged under water.  This method is not widely available and expensive; however it is accurate with only a 2.7% degree of error.

Bioelectrical Impedence Assessment (BIA).  BIA is found in most gyms and health clubs and uses the electrical resistance throughout a person’s body to estimate their overall body fat percentage.  This method is not very accurate since it can be affected by hydration levels, how soon prior to the test you have exercised and food intake.  Additionally, it doesn’t take into account belly fat specifically which can be the most dangerous area to retain fat.  However this test is widely used in health fair and gym settings since it is non-intrusive and very inexpensive.

For all methods, athletic to average males should range in the 12-20% range for body fat and females should fall between 18-25%. While working for 8.2% body fat may be a noble venture, more general and realistic goals like dropping 1-2 clothing sizes and healthy personal perceptions will serve the average person best without the cost of any extra equipment.  When using any body-fat measurement technique, remember that every person needs to have some level of fat in their body for proper function and getting hung up on exact numbers can be discouraging and misleading.  The key is to stay active and maintain a proper diet to satisfy your own health goals.

Thanks for reading!

Contributors: Kim Farmer and Terry Hackney of Mile High Fitness.  Mile High Fitness offers in-home personal training and corporate fitness solutions.  Visit  www.milehighfitness.com or email inquires@milehighfitness.com

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