This is the third in a series on weight loss. In my first installment, I discussed the distinction between weight loss and fat loss. As you lose fat, it’s important to maintain muscle, or at least minimize muscle loss. I also discussed the limitation of the scales. They’re not an accurate way to track this process. In this article, I’ll present the concept of body composition and describe several methods for predicting it.
Your body is composed of many types of materials. Some tissues, like skin and muscle are primarily protein. Other tissues have a high fat content, such as the liver, nervous system and, of course, fat cells. Still other tissues, especially teeth and bones are made of mostly minerals. Fifty to 70% of your body is water, depending on age, gender and level of hydration.
If your task is to plan a weight loss/management program, you want to begin by knowing what percentage of your body weight is fat (called percent body fat; PBF) and what percentage is everything else. The weight of everything that isn’t fat is called lean body mass (LBM). As an exercise physiologist advising you, my concern is primarily with two tissues, adipose (fat deposited under the skin and centrally) and skeletal muscle. I want to help you lose fat while preserving as much muscle as possible.
Maybe fat loss is not your goal. Maybe you’re an athlete working to increase muscle mass. Seniors and those recovering from illness may also have a goal of gaining muscle. Here too, knowing how much muscle you currently have is a good benchmark. Since few other components of LBM (other than fluids; more about that later) change over time, increases in LBM can be thought of as increased muscle mass.
Body Composition Analysis
Regardless of whether fat loss or muscle gain is your goal, it’s worthwhile to establish a baseline prediction of body composition. I use the word, “prediction,” and not, “measurement,” deliberately. The only direct measurement of body composition is as part of a postmortem. (I don’t expect anyone will want to sign up for that.) All other methods are based on some assumptions and statistical methods. All body compositional analysis methods obtain some data, which get plugged into a formula and yield results that are best thought of as predictions. Several methods have been used for decades for these predictions. In more recent years, newer methods have become available.
These have been widely used for decades. They measure the thickness of a fold of skin, and the fat underneath, in millimeters. The measurements are plugged into a formula which produces PBF. Accuracy is as good as ±3.5%, but is highly dependent on technique. Some people find the process of being pinched—especially in certain parts of the body—undesirable.
This is another long- and well-established method. It involves submerging your body completely underwater and being weighed while submerged. Since fat is less dense than water, it floats. The greater the PBF, the lower the body density and the lower the underwater weight. This method requires equipment typically found only in research settings. In Tallahassee, the only way you’d ever get weighed underwater is if you were a participant in a study at FSU, or a varsity athlete.
Dual-energy x-ray absorptiometry (DEXA) is mostly used for assessing bone mineral density and diagnosing osteoporosis. Since x-rays at different energy levels are absorbed at different rates, by different tissues, it can distinguish between them. Due to the cost of these devices, they are only found in clinical and research settings. The DEXA scan you might get for your bones is unlikely to have any info on body composition, because this requires special software. Like underwater weighing, you’d have to be in a research project at FSU to have this type of analysis.
This device uses air displacement plethsmography which, like underwater weighing, measures body volume and estimates density. From these it predicts PBF and LBM. A new Bod Pod will cost over 30K. The only one in town is at FSU, but you’d have to be a student or employee to use it.
Conventional Bioelectrical Impedance (BEI)
These devices have been around since the mid-80s. They work by passing an imperceptible electric current in one electrode and measure it at another. The difference between the two is the impedance of your body. Since fat has a high impedance and lean tissues have lower ones, these devices distinguish between the two—theoretically. The complication is that these cannot account for how much water is in your body at the time of the test. One of my physiology profs in college said, “You are a highly compartmentalized bag of salt water.” All the fluids of the body contain dissolved minerals called electrolytes. This makes these fluids good conductors of electric current. If you are well dehydrated one day, and well-hydrated another, you’ll see very different results. These different results ignore the possibility that your actual fat mass and lean mass may not have actually changed. Conventional bioelectrical impedance cannot account for how much water is in your body at the time of the test.
Multi-frequency Bioelectrical Impedance
Unlike conventional BEI, the most advanced versions of these devices use three frequencies to distinguish between fat, muscle and water, both inside (intracellular) and outside (extracellular) of cells. They also scan the whole body and analyze each limb and the torso independently. By taking water into account, we can now more accurately predict body composition. The relationship between intracellular and extracellular water is an emerging area of interest for health professionals. Excess extracellular water can be associated inflammation, diabetes, heart failure, kidney disease, obesity and other conditions. For the first time track your fat mass and muscle mass reliably over time. Several models of these devices exist in the Tallahassee area in clinical, research and fitness settings.
No totally accurate body composition analysis is possible on a living person. All methods have a built-in degree of error. Failure to follow exact procedures for any method will result in additional error. For accuracy, reliability (accuracy from one test to another), accessibility, economy and ease of use, multi-frequency BEI seems to be the best choice. As always, if I can be of help with this, or anything else, please contact me at the below.
To learn more about how Premier Health & Fitness Center can help you determine your body composition, call 850-431-BFIT.