Are Body Mass Index (BMI) Tables Effective Enough?

By: Rajeev Kumar


The most common method of determining ideal weight is the height and weight chart. These tables, guide you how much you should weigh based on your height. Although these tables are still popular, they are very inaccurate, specially to athletes and bodybuilders who carry more muscle than most people do. “Ideal weights” from height-weight tables do not take body fat into account; therefore, they cannot accurately recommend how much you should weigh.

Body Mass Index (BMI) is another common way to determine whether someone is at a “healthy weight”. Like the height and weight tables, BMI is a poor measure of good health because it takes only height and weight into account. In addition, it does not take into account fat versus muscle tissue. Body builders and other athletes carry more lean body mass than the average person and will therefore be classified as overweight if BMI is used as the basis for determination.

The significance in measuring body fat percentage is so you can tell between fat and muscle, which the ideal weight and BMI calculator does not. Average body fat percentage vary among the sexes and among different age groups. The female hormone estrogen causes women to have about 5% more body fat than men. The average woman has about 23% body fat and the average man approximately 17%. In both sexes, body fat increases with age while lean body mass decreases. The following are the techniques widely used for determination of body fat percentage.

Underwater Weighing (Hydrostatic)
Underwater Weighing has always been considered the best for measuring the body fat percentage in comparison with other measurement techniques. The basis for hydrostatic weighing is the fact that fat floats and muscle sinks. To measure your fat by underwater weighing, the person should remain dipped underwater in a chair that is hanged from a scale. The fatter you are, the more buoyant you will be, and the more buoyant you are, the less you will weigh underwater. Notwithstanding, underweight weighing has its own inconveniences; the major one is the inconvenience of being dipped in water. Notwithstanding, underwater weighing underestimates the fat percentage for persons with denser bones. Unless race, age, and sex are all carefully taken into account, the estimate of body fat could be having a serious error. To summarize, underwater weighing is not very practicable, though it is always interesting to go get it done once in a while just for pleasure.

Bio- Electric Impedance Analysis
Bioelectric Impedance Analysis (BIA) is a sophisticated scientific instrument that measures body fat percentage by testing the electrical resistance of your body’s cells to a flow a small harmless electrical signal. Fat has a low water content compared to muscle, so has an insulating effect, and is therefore less conductive. Research shows that BIA is a fairly reliable and valid measure of body fat percentage. The impedance measure is affected by body hydration status, body temperature, time of day, and therefore requires well controlled conditions to get accurate and reliable measurements. If a person is dehydrated, the amount of fat will likely be overestimated.

Near Infrared Interactance
Near Infrared Interactance (NIR) is based on light absorption and reflection to determine body fat percentage. The measurement is taken on the person’s dominant arm. The light wand sends a beam of infrared light into the body where variations in the reflections of the wavelengths are used to estimate total body fat percentage. The measurement is very safe, simple and easy to use with less practice. The inconveniences include the high cost of the machine, and the questionable accuracy and reliability like it assumes fat in the arm is proportional to total body fat, which may not be true.

Skinfold Measurement
Skinfold testing is based on the fact that most of the body fat is stored directly below your skin. The skinfold test is performed with a simple instrument called a skinfold caliper. The jaws of the caliper pinch a fold of skin and fat and measure the thickness of the fat fold in millimeters. Using the calipers, skinfolds measurements are taken at different sites around the body and then the measurements are added up. The sum of the skinfolds is then looked up on a body fat estimate table that comes with the calipers. A proficient tester can produce a body fat measurement with accuracy very close to underwater weighing, which is considered to be standard of body composition testing. Most importantly, skinfold testing is extremely practicable and lot more simpler than many of the measurement techniques. However, the reliability of the measurements may vary from tester to tester.

Other Methods
There are many other methods used to determine body fat percentage, including Total Body Potassium, Dual-Energy X-Ray Absorptiometry (DEXA), Total Body Electrical Conductivity (TOBEC), Whole-Body Air-Displacement Plethysmography, Magnetic Resonance Imaging (MRI) and Computed Tomography (CT scan). While some of these modern methods may be incredibly reliable and useful in the laboratory, none of these methods is practical at least for personal use for a weight loss program.

Now you came to know the importance of body fat versus body weight and you understand that height and weight and Body Mass Index (BMI) tables are worthless. It is also clear that losing weight is not of prime importance, but losing fat is.

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