Human body composition models and methodology : theory and experiment

The study of human body composition is a branch of human biology which focuses on the in vivo quantification of body components, the quantitative relationships between components, and the quantitative changes in these components related to various influencing factors. Accordingly, the study of human body composition is composed of three interrelated research areas, body composition rules, body composition methodology, and body composition alterations. This thesis describes the authors recent investigations related to the first two of the three research areas. In the rules area, this thesis begins with a comprehensive five-level model of body composition. The approximate 40 body components are systematically organized into five levels with increasing complexity: 1, atomic; 11, molecular; III, cellular; IV, tissue-system; and V ₁ whole-body. Although each level and its multiple components are distinct, interconnections exist such that the model is consistent and functions as a whole. The model provides the opportunity to define clear body composition concepts and to create explicit body composition equations. As an example of a body composition rule, this thesis subsequently explores the magnitude and constancy of the proportion of adipose tissue-free body mass as skeletal muscle mass in young healthy adults.

In the methodology area, this thesis begins with a systematic organization of body composition methods. The proposed classification divides the methods into in vitro and in vivo categories, advances to organization- by measurable quantity (property and/or component), and ends with grouping of methods by mathematical function which may be statistically-derived or model-based. This classification system explains both similarities and differences between the many diverse methods, and provides a framework and a setting for all body composition methods. As an example of new body composition method development, the subsequent chapter creates a simple and safe method for predicting total body oxygen mass from body weight and total body water. The remaining four chapters deal with the evaluation of body composition methods. A six-compartment model based on in vivo neutron activation analysis is applied as the reference for inter-method comparisons against sixteen existing methods for estimating total body fat mass. An advanced technique, multiscan computerized axial tomography, is applied as the reference to evaluate existing skeletal muscle mass methods, including the Burkinshaw-Cohn neutron activation model, dual-energy X-ray absorptiometry, 24-hour urinary creatinine excretion, and 24-hour urinary 3-methylhistidine excretion methods.

This thesis, therefore, suggests that both theoretical and experimental investigations provide insight into human body composition.