Frequently Asked Questions

The user's guide for your software should have a brief description of each of the equation sets, and why it was created. (It may be in the FAQ section in the back.)

In general, most people tend to use the "NHANES-III" equation set. The equations for fat and fat-free mass, and total body water were developed as part of the Fels Longitudinal Study, which collected information about a large cross-section of the American population. A second study was done which showed how the equations performed on data collected in the NHANES-III survey, which also included a large cross-section of the American population. As a result, it tends to provide good estimates for body composition for individuals with relatively nondescript body types — that is, they resemble a "typical American of their sex and (approximate) age."

However, for people who do not resemble the general population, the accuracy of these equations will tend to degrade. For example: for people who are very thin or very skinny, or who, when you look at them, you can say "Just by looking at you, I can tell that you work out on a very regular basis," the NHANES-III set will tend to over-estimate body fat. For these people, we generally recommend the "Athletic" equation set. On the other end of the spectrum, for people who are very obese, the NHANES-III equations will tend to under-estimate fat. For these people, the "Obese" equation set will likely provide a more accurate estimate.

There's more to being male (or female) than just your genitalia. As we grow, our gender affects how our bones, muscles, etc. grow, and how fat is distributed throughout the body. Because of this, equation sets will typically use different formulas to estimate body composition based on gender. When entering data for a person, you should always use their biological sex/gender, regardless of which gender they currently self-identify as.

To answer that question, it helps to review some history. RJL Systems received its first 510(k) clearance from the FDA to distribute a BIA Body Composition Analyzer in 1983. Once you have permission from the FDA to distribute a medical device, there are rules on what sorts of changes that you are allowed to make to the cleared product before you have to go back to the FDA and get a new clearance. In 1986, we developed the BIA-103, which was a stand-alone system that integrated the BIA with an off-the-shelf portable computer. Because our previous clearance was for a BIA  and accompanying software, and not for a computer with a built-in BIA, we needed a new 510(k), which we were granted in 1987.Fast-forward to the mid-1990s. Body composition researchers rediscovered the idea of subdividing Fat-Free Mass into “metabolically active cells” (called Body Cell Mass, or BCM) and “everything else” (called Extra-Cellular Mass, or ECM) – an idea first published in 1963. Papers were published in scientific and medical journals that showed that BCM and ECM could be estimated using BIA with a reasonable amount of accuracy. Some of these researchers approached RJL about adding these (and other) values to those already being calculated by our software.

RJL management reviewed the rules on making changes to a device and concluded that, since all they were proposing was to calculate a few additional values from information that the company was already cleared to collect and report, a new 510(k) clearance was not required. RJL developed and released the “Fluid and Nutrition Analysis” (abbreviated as “FNA”) program for computers running MS-DOS. In the late 1990’s, RJL updated FNA to take advantage of the graphical capabilities of Windows, and named the result “Cyprus”.

RJL management was wrong. In a document the FDA published in 1997 in an attempt to clarify the rules, they state that any change that adds to the list of values being reported (or “Indications for Use”) generally requires a new 510(k) clearance. Despite regular contact with the FDA, RJL was not made aware of this document or that there was a problem until 2005. At that time, RJL realized that they could not legally continue distributing Cyprus. As a result, Cyprus was discontinued and replaced with “Lean Body”, which only reported the values that RJL had clearance for, and RJL began the process of trying to get clearance for the “new” values found in Cyprus.

Eventually, in 2007, RJL was able to get clearance to report “Intra-Cellular Water” (ICW) and “Extra-Cellular Water” (ECW) – the amount of water found inside the body’s cells and the remaining water outside the cells, respectively — and RJL released the program titled “BC (Body Composition)”.

The remaining values that were removed from the Cyprus program (BCM, ECM, Capacitance, and Impedance Index) are “new” in the sense that no clinical utility of these values has been demonstrated to the satisfaction of the FDA, and as a result, no medical device may be distributed in the United States that reports them, until such time as a manufacturer either receives a Clearance or Approval from the FDA.