In this blog post, we’ll take a detailed look at the main types of body composition tests and the principles and characteristics of bioelectrical impedance analysis (BIA), commonly known as “InBody.”
Every year when the New Year rolls around, many people resolve to lose weight and sign up for a gym membership. Upon joining a gym, they typically undergo a body composition test known as “InBody.” Whereas in the past, the number on a scale was the sole criterion for determining obesity, today body composition tests are used to evaluate obesity by comprehensively considering a wider range of factors. In fact, there are several types of body composition tests. “InBody” is one of them, and its official name is Bioelectrical Impedance Analysis (BIA). However, most people are more familiar with the term “InBody” than with “body composition test.” Therefore, in this article, we’ll take a closer look at the main types of body composition tests and what Bioelectrical Impedance Analysis (BIA)—commonly known as “InBody”—actually is.
Body composition tests include DEXA, underwater weighing, and Bioelectrical Impedance Analysis (BIA). DEXA stands for Dual-energy X-ray Absorptiometry. DEXA provides detailed information on the body’s composition—such as fat, muscle, and bone—and is known for its high accuracy. However, the test tends to take a relatively long time. In addition, the underwater weighing method uses buoyancy to measure body composition. Since it calculates body fat by measuring weight underwater, it allows for accurate body fat measurement; however, it requires the user to enter the water, which can be inconvenient, and the density of water can vary depending on water temperature, so it is not widely used today. Finally, bioelectrical impedance analysis (BIA) is easily accessible in daily life, and the measurement equipment is relatively inexpensive.
Commonly referred to as “InBody,” bioelectrical impedance analysis (BIA) is a method that measures body composition by passing a very weak alternating current through the body at a level that does not affect the human body. BIA analyzes body composition by utilizing the differences in electrical conductivity and electrical resistance based on the biological characteristics of tissues. The electrical conductivity of human tissues is influenced by the amount of water and electrolytes, and adipose tissue is less electrically conductive than muscle tissue. Therefore, adipose tissue exhibits high electrical resistance, while muscle tissue, which has a high water content, exhibits low electrical resistance. Based on this principle, bioelectrical impedance analysis estimates body fat mass and muscle mass by combining the measured electrical resistance values with basic information such as height and weight.
However, since the bioelectrical impedance analysis method is highly susceptible to changes in the body’s hydration status, measurement errors may occur. For example, even if a person has the same amount of body fat, an increase in body water content can lower the electrical resistance value, resulting in a body fat measurement that is lower than the actual amount. To minimize such errors as much as possible, it is advisable to follow a few guidelines before taking a measurement. For more accurate results, it is best to take the measurement approximately 4 hours after a meal and about 30 minutes after using the restroom, rather than immediately after eating or urinating. It is also advisable to avoid strenuous exercise before the measurement. In particular, for women, measurement errors can be significant during menstruation due to changes in body water content; therefore, it is preferable to avoid measurements during this period if possible.
Currently, devices that are smaller and more convenient than traditional bioelectrical impedance analyzers are being continuously developed, and technologies to reduce measurement errors are also steadily advancing.
We have now entered an era where it is easy to use scales at home that not only measure weight but also provide body composition data. As bioelectrical impedance analysis becomes increasingly common in our daily lives, it is important to correctly understand its principles and be familiar with the measurement conditions and precautions to ensure accurate results.
