[ARTICLE] Measurement of body composition: concept and tools

As developed in our previous article on  , the type of data obtained are useful for diagnosis, managing and understanding different physiological conditions such as weight loss, sarcopenia or others disease risk factors.

Concept

Analysis of body composition is based on different models, mainly the following (1,2): 

Two compartment model (2C): the simplest approach dividing body weight into fat mass (FM) and fat-free mass (FFM). FFM includes internal organs, bone, muscle, water, and connective tissue.

Examples of tools based on this model: hydrodensitometry, air displacement plethysmography and hydrometry.

Three compartment model (3C): body weight is divided into fat mass (FM) and fat-free mass (FFM) which is then, divided into lean tissue mass and bone mineral content (BMC).

Examples of tools based on this model: The dual-energy X-ray absorptiometry (DXA).

Four compartment model (4C): this model divides the body into fat, water, protein (metabolic tissue) and mineral.

Tools

Different tools are available for the assessment of body composition: (1)

CT scan: A high-resolution, three-dimensional volume image of parts of the body, using X-ray projections from different angles of the body. The attenuation differences between X-rays of lean soft tissue and adipose tissue are used to separate these tissues.

Magnetic Resonance Imaging (MRI): Images of soft tissue in the body can be produced by MRI, which uses the different magnetic properties of the nuclei of the elements in the cell (usually hydrogen) in both water and fat. In this technique, the separation of the signals into water and fat images is made using the magnetic resonance frequencies of protons. Since the MRI does not use ionizing radiation, it can be used for three-dimensional volumetric imaging even in neonate and infants.

Dual-Energy X-Ray Absorptiometry: The principle of the DXA is that the attenuation of X-rays with high and low photon energies is measureable and depends on the properties of the underlying tissue. The variations in the attenuation of X-ray through the tissues are caused by differences in the density and chemical composition of fat, lean tissue and bone.

Bioimpendance: Measuring the impedance to the flow of a low-electrical current (800 μA), at a fixed frequency (50 kHz). The principle of bioimpedance is that lean tissue, consisting of water and electrolytes, is a good electrical conductor, while fat, which does not have water, is a poor conductor. Total body water obtained is converted to fat-free mass via the assumption that 73% of the body’s fat-free mass is water (3).

Air displacement plethysmography (ADP):  Measures body volume through air displacement inside a sealed chamber (4).

Skinfold thickness: A skinfold caliper is used to assess the skinfold thickness, leading to an estimation of the total amount of body fat. This is based on the hypothesis that the body fat is equally distributed over the body, which is not reliable.

Infants and children

Body composition could be used also for infant as a marker of fetal adaptation and developmental programming of subsequent health and disease. Methods currently used in infants from 0 to 2 years of age, include anthropometric prediction equations, air displacement plethysmography (ADP), dual energy X-ray absorptiometry (DXA), bioelectrical impedance analysis (BIA), isotope dilution, and magnetic resonance imaging (MRI). In the case of infant research studies, DXA is increasingly used to assess regional adipose tissue and lean mass, while for anatomic-level analysis, magnetic resonance imaging (MRI) is most often used, as computed tomography (CT) involves significant subject exposure to ionizing radiation (5).

Recommendations

Many tools are available to assessed body composition and correct choices regarding the objective need to be done. For example, to be able to measure visceral fat, tools as DXA and MRI are more accurate, as the others tools do not allow this measure.

The European Food Safety Agency (EFSA) recommends to assess body composition by “using methods with appropriate validity and precision, imaging techniques (e.g. DEXA, MRI and CT) are generally appropriate to assess changes in lean body mass in human intervention studies. BIA and ADP may not be appropriate to assess small changes in lean body mass when used alone, particularly in obese subjects and/or when significant changes in body water compartments occur.” (6)

In addition, some reviews have concluded to the superiority of DXA tools for the reliability and precision of the data in clinical research (see also our infographic about Dxa) (3,7,8). However, in order to answer in the most efficient way to the research hypothesis assessed in a clinical trial, a review of the commonly used tools is done before each study.

References:

1. Kuriyan R. Body composition techniques. Indian J Med Res. 2018 Nov;148(5):648–58.
2. Kuriyan R, Thomas T, Ashok S, J J, Kurpad AV. A 4-compartment model based validation of air displacement plethysmography, dual energy X-ray absorptiometry, skinfold technique & bio-electrical impedance for measuring body fat in Indian adults. Indian J Med Res. 2014 May;139(5):700–7.
3. Aragon AA, Schoenfeld BJ, Wildman R, Kleiner S, VanDusseldorp T, Taylor L, et al. International society of sports nutrition position stand: diets and body composition. J Int Soc Sports Nutr [Internet]. 2017 Jun 14 [cited 2019 Aug 13];14. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5470183/
4. Lemos T, Gallagher D. Current body composition measurement techniques. Curr Opin Endocrinol Diabetes Obes. 2017 Oct;24(5):310–4.
5. DEMERATH EW, FIELDS DA. Body Composition Assessment in the Infant. Am J Hum Biol. 2014;26(3):291–304.
6. EFSA Panel on Dietetic Products N and A (NDA). Guidance on the scientific requirements for health claims related to appetite ratings, weight management, and blood glucose concentrations. EFSA Journal. 2012 Mar 1;10(3):n/a-n/a.
7. Lee SY, Gallagher D. Assessment methods in human body composition. Curr Opin Clin Nutr Metab Care. 2008 Sep;11(5):566–72.
8. Marra M, Sammarco R, De Lorenzo A, Iellamo F, Siervo M, Pietrobelli A, et al. Assessment of Body Composition in Health and Disease Using Bioelectrical Impedance Analysis (BIA) and Dual Energy X-Ray Absorptiometry (DXA): A Critical Overview. Contrast Media Mol Imaging [Internet]. 2019 May 29 [cited 2019 Aug 12];2019. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6560329/