By PhD Dr. Kathrin Bieri, Head of Science at Bodygee
Recently, I have been asked so many questions about the measurement of body fat, that I decided to dedicate my first blog post to this subject.
First of all, the most important fact: body fat cannot actually be measured. At least not on living human beings. Strictly speaking, the word "body fat measurement" only applies to an "in vitro" analysis, i.e. the anatomical dissection of a cadaver. "In vivo" analysis should be correctly referred to as a "body fat estimate". These measurement methods are not easy to understand, which is probably why the assumption that body fat can actually be measured is still as widespread as ever. So let me explain the methods in more detail:
Generally, the estimation of body fat is based on the calculation of specifically analyzed properties of the body. The most precise method nowadays is considered to be the MRI or CT scan. High-resolution, anatomical cross-sectional images enable the volume of fat, skeletal muscles and other tissues and organs to be assessed. However, this is a very expensive and elaborate process. Therefore, the much less expensive dual X-ray absorptiometry (DXA) is the most widely used laboratory method, especially for scientific purposes. DXA is an X-ray procedure that measures the different attenuation of the rays by various types of human tissue. This enables fat, bone and lean mass to be calculated. However, the cheapest, and probably the best known laboratory method in the fitness industry, is still the so-called air displacement plethysmography (known as "Bod-Pod"). The body density of a person is determined by measuring the displaced air volume inside a closed chamber. Since the density of the fat-free mass is different from that of the fat mass, the body fat can be calculated accordingly.
Screenshot of a DXA scan. This method is often used scientifically, in order to determine body fat. Source: Shepherd JA, Ng BK, Summer MJ, Heymsfield SB (2017) Body composition by DXA. Bone 104:101-10
Nowadays, the measurement methods commonly used in the fitness industry are all derived from one of the laboratory method mentioned above, therefore they are referred to as "field methods". The methods are all based on the same basic principle: first of all, a specific body characteristic is also measured here. For example, the Bioelectrical Impedance Analysis (BIA) measures the resistance to electric current, the calipers measure the thickness of skin folds and the 3D body scanner measures the circumference and volume of the body. The body fat is then calculated by means of mathematical formulas (which, as I said, are derived from laboratory methods). If laboratory methods can be regarded as indirect measurements, field methods are even more indirect, because they are based on multiple estimates and assumptions. This fact increases the probability that the estimated fat value could deviate from the (unknown!) truth. The advantage of field methods, however, is that they are usually inexpensive and easy to apply.
It is obvious that we have to accept that body fat measurement provides a good estimate of the percentage of body fat (at best). Nevertheless, fat measurement can and should be a central component of the fitness customer support. In order for this to be successful, it is important to offer high quality standards. At Bodygee, we attach great importance to using a scientific formula; whereby research methods and calculations are openly presented in scientific journals. In addition, we see reproducibility (also referred to as "reliability") as a central criterion of quality. For fitness customers, the focus is often not on absolute values, but on changes over time. The reproducibility is determined by precise compliance with the measurement guidelines, which we intensely teach in our training courses.
Bodygee 3D scanning. In order to ensure accuracy, compliance with the measurement guidelines is extremely important.
Our table gives you an overview of the most important methods for the measurement of body fat and their advantages and disadvantages.
Kathrin Bieri from Switzerland studied Sports Science and graduated from the University of Berne with a Doctorate in Sports Medicine. She is a passionate sportswoman herself and spends several evenings at the gym every week.