What Is Body Composition?

Generally speaking, body composition is way of expressing the way a person’s weight is distributed. It’s usually thought of as a ratio comparing the weight of bone, muscle, fat, and water. There are a couple of different ways to come up with these measurements, some of which are more precise than others. In most cases measurements are done to give medical professionals some insight into whether a person is at a healthy weight. Calculations are usually intended to figure out where weight is coming from, which can give a lot more insight into why a person registers a given number on the scale. High weights that are attributed to fat deposits are usually thought to be problematic, but if dense bones and muscle fibers are causing the higher number there may not be any cause for concern. Body composition analysis isn’t always a standard part of a medical workup, but it usually is if a person’s weight is higher than it should be. Getting an accurate breakdown can help medical professionals design specific and individualized plans and diet options.

There are lots of reasons why maintaining a healthy weight is import for people of all ages, but there are also lots of explanations for weight that might seem higher than expected. What body composition demonstrates is that not all weight is “bad” weight. Most of a person’s mass is directly attributable to things like bones, water, and muscles — all of which are important if not essential. Some weight attributed to fat is also usually considered healthy since fat, in moderation, does perform some important functions. Composition calculations can help care providers understand where a person’s weight is coming from, which can differentiate whether a person just has a naturally high mass or whether he or she is truly overweight.

Most of the guidelines for compositional ideals that have been published by regulatory agencies and national health authorities focus on fat percentages. In general, the consensus seems to be that, for optimal health, a man’s body should consist of between 8 and 17 percent fat, and women should strive for a 20 to 21 percent body fat maximum. If a person is more athletic or muscular, body fat percentage can be a bit lower, usually falling between 7 and 19 percent for men and 10 and 25 percent for women. Numbers that are higher than these ranges are usually signs of obesity, which is linked to a number of different health problems and conditions.

There are a few ways that body composition can be measured. The most widely used method requires a set of calipers, a medical tool that looks a bit like tongs or enlarged tweezers, that physically measures the thickness of the fat below the skin. Commonly measured areas include the abdomen, thighs, and arms. These measurements are used to estimate how much total body fat is present, but the caliper test can have a margin of error of roughly 4 percent. It’s also important to note that this method really only assesses fat levels. Bone, water, and muscle densities usually have to be either estimated or measured in some other way.

A far more accurate way to measure body fat is with bioelectrical impedance analysis, followed by air displacement plethysmography (ADP). During the later test, a person enters an airtight chamber and his or her body volume is measured by the displacement of the air inside. Body volume and mass combine to determine density, and the percentage of body fat versus lean muscle mass is calculated in the process.

It is also possible to achieve a body volume index reading with a dual energy X-ray absorptiometry (DEXA) scanner. The measurements given by this machine tend to be the most accurate and include bone density, mineral content, fat tissue mass, and lean tissue mass. Computed tomography (CT) and magnetic resonance imaging (MRI) machines can be accurate as well, making each a good choice for doctors that are monitoring a patient's body fat as a means of monitoring overall health.