Chapter 13– Measurement of Human Body Composition toAssess Obesity

Questions

  1. What are some of the reasons for measuring body composition?
  2. What would be the characteristics of an ideal body composition method?
  3. What major body composition methods are not suitable for a field-based setting and why?
  4. What major body composition methods are not suitable for infants or children and why?
  5. What assumptions are used in the 2-compartment model for calculating fat content from measurement of total body volume by underwater weighing?
  6. What body components would be measured for a study using a 4-compartment model of body composition?
  7. What method has been used to distinguish lipids within the muscle cell and outside of the muscle cell (but still within muscle tissue)?

Chapter 13– Measurement of Human Body Composition to Assess Obesity

Answers

  1. The over-arching purpose of body composition measurements is to identify normality/disease by determining if composition differs from what it should be for optimal health.
  2. An ideal body composition method would be safe, quick, and inexpensive. They also should be designed to allow only minimal measurement error, be applicable to all living persons regardless of age, sex or ethnicity, and require only limited technical training and subject cooperation.
  3. Methods that are not suitable for field-based settings include DXA (dual x-ray absorptiometry), underwater weighing, air plethsmography (the Bod-Pod or Pea-Pod), and imaging methods, such as MRI, CT, and DXA. Generally these methods require expensive, specialized, and complex equipment, as well as extensive technical training of the operator. Some also require significant cooperation of the subject (e.g., air plethesmography and underwater weighing).
  4. Methods not suitable for children include those involving high radiation exposure (e.g., CT), underwater weighing, and those that require more cooperation than is routinely possible.Dilution methods are difficult because of the problem of collecting adequate urine from an infant or child.In practice, only a few methods are totally excluded for use with children.
  5. When body volume is used to estimate body fat using a 2-compartment model, the density of the lean tissue is estimated by making assumptions about its proportions of water, protein, mineral, etc., based on the various theoretical models of the body. The known densities of fat (lipid) and water are also used in the calculations to estimate body fat. This model does not take account of differences in bone mineral and the degree of hydration in different subjects, which makes it most inaccurate in conditions where they differ from the model used.
  6. The four quantities measured can be body volume or body density, total body water, bone mineral, and body mass/weight.These measurements cover the components that vary most from subject to subject and whose variations have the largest effect on body density (i.e. body water and bone mineral). With them, very limited assumptions need to be made about the details of the other (minor) components of the body.
  7. Magnetic resonance spectroscopy is able to distinguish these two lipid locations.

Understanding Obesity: Biological, Psychological and Cultural Influences. Edited by Sharon Akabas, Sally Ann Lederman and Barbara J. Moore. © 2012 John Wiley & Sons, Inc. Published 2012 by John Wiley & Sons, Inc.