Assessment Methods in Human Body Composition
Body composition measurements, though varying in methods and depth of certain bodily components, aim to better understand health risk related condition that are generally associated with certain diseases or conditions. To better organize the different methods of assessment, a five level model was created to provide a framework to better assess the human body.
Beginning with atomic, measuring 11 components which are ions in the body to calculate body mass, the second being molecular. The molecular level uses six components, including fat mass, total body weight, mineral compositions and carbohydrates to estimate fat free mass. The cellular level using four levels that include fat mass, cell mass, and cellular fluids to calculate body mass. The fourth level, labeled the tissue-organ level consisting of five components, adipose tissue, skeletal muscle, bone, visceral organs and other tissues. The fifth and final level is the entire body, which divides components into head, trunk and appendages. These levels are then assessed through the use of varying methods and devices, depending on the respective setting.
First discussed is a bioelectrical impedance analysis (BIA) and bioimpedance spectroscopy. This device utilized the 2C portion of the model, by providing a small electrical current and measuring the resistance as it propels through water in the body. The BIA has a minimal cost, is simple to use and due to itsportability is preferred for larger sample sizes. Issues in validity and reliability for this assessment, stem from the participant’s demographics such as age, sex, ethnicity and other aspects such as previous exercise and hydration status.
The goal standard of body composition, dual energy X-ray absorptiometry (DXA), provides total body or regional estimations of bone mineral, bone free fat free mass and fat mass. The controversy on radiation exposure while implementing this device has become increasingly popular but studies have shown only 1-10% of the exposure of a chest radiograph. Though with elevated levels of accuracy and reliability, some assumptions made through this device can alter the measurements of individuals based upon their level of free fat mass or fat mass. Those with relatively increased fat mass, will have a greater error when measuring fat free mass and opposite is true for individuals with less fat mass.
Methods such as quantitative computed tomography (QCT) and varying dilution technique have been implemented to assess body composition. Limited evidence supports the effectiveness of QCT related measurements, but can potentially measure body mass densities but presents a higher level of radiation than the DXA. Dilution helps to separate differing water components of the body, by presenting various isotopes. These recording can then be used to estimate the total body weight, fat mass and fat free mass, with the assumption of stable hydration in fat free mass.
Air displacement plethysmogrpahy (ADP) records body volume and fat mass through measuring the volume of air displaced by the participant. Validity and reliability are high when assessing a healthy adult individual but some error may occur, resulting in an overestimation of fat mass. Another method developed to measure volume, as well as dimensions, is the three-dimensional photonic scanner. Producing a three-dimensional image, the scanner estimates volume and dimensions for the individual, but research has shown this method may overestimate some of the variables. This form of assessment is commonly used for epidemiological studies to better understand correlations between overall body shape and certain health risks.
The usage of MRI is implemented to estimate adipose tissue, skeletal muscle, and other related tissues, to locate distribution of fat mass. This measurement can also be utilized for further analysis of differing metabolic rates of organs, in vivo. Information on this metabolic rates present greater insight into an individual’s resting metabolic rate. The major disadvantage of this method is that the size of the machine may not accommodate all body types and sizes, due to the smaller field-of-view that the machine scans. Similar to MRI, other devices using magnetic resonance but analyze more complex components.
Quantitative magnetic resonance (QMR) measures the differences between nuclear magnetic resonance aspects of hydrogen atoms within fat mass, lean tissues and free water. When assessing validity and reproducibility of these measurements, there was an underestimation of fat mass and over estimated lean mass, leading to some deviation across repeated measures. The final method described is positron emission tomography (PET) to assess brown adipose tissue, a popular component of investigations into fat loss.
New research and evidence leads to greater advances in methods and assessments of body composition. This pursuit of developing valid and reliable methods provides greater understanding into the variables we hope to assess and analyze. The methods discussed can lend greater insight to the true impact of the body composition and the potential health risks associated with varying body types.