Measurement of Total Energy Stores
STEVEN B. HEYMSFIELD
Total body energy stores are distributed into a number of body composition compartments or components. Figure 22.1 shows the traditional energy stores at the molecular level as three components: lipid, proteins, and glycogen (i.e., carbohydrate). The corresponding tissue systems are adipose tissue, skeletal muscle, and other organs and tissues. With weight gain or loss, there may be changes in the size of compartments at all levels of body composition analysis.
The aim of this chapter is to review the main methods of quantifying each of the major body compartments related to total body energy stores. Two major groups of methods are presented: laboratory methods and clinical or field methods.
Simple radiographs were used in the 1950s to quantify soft tissue composition and bone. By the mid-1970s, computerized tomography (CT) was introduced and subsequently became a major method of evaluating human body composition. The method produced high tissue contrast, allowing clear separation of anatomic components including adipose tissue, skeletal muscle, bone, and visceral organs. The cross-sectional imaging procedure allows three-dimensional reconstruction of body compartments and examination of components not previously evaluated such as visceral adipose tissue. Unlike computerized tomography, magnetic resonance imaging (MRI) uses nonionizing radiation. Images of compartments created with MRI are almost equivalent to those of CT. The one exception is visceral adipose tissue, which is less highly resolved by MRI than CT because of peristaltic movement through the gastrointestinal tract. Once images are created by CT and MRI, they are analyzed slice-by-slice and combined to determine the volume of each