Any appraisal of human fatness requires consideration of the spectrum of adiposity across mammals in general. Humans have often been described as a relatively fat mammal (Brown and Konner 1987), yet until recently empirical data on a wide variety of species were sparse. In this chapter the body composition of human adults is compared with that of other mammals, addressing both the total mammalian range and also the body composition characteristic of other primate species. It is equally important to consider the variability within the human species by reviewing data on between-population variability. At this stage, these analyses will be restricted to adult data, as the ontological development of body composition is addressed specifically in Chapter 4.

The gold standard for body composition analysis remains cadaver dissection. For the majority of studies both on non-human animals, and particularly on humans themselves, this approach is clearly inappropriate. Assessment of body composition therefore generally requires the measurement of whole-body properties such as density, and the use of theoretical assumptions and mathematical models to convert those raw data into final body composition values. A variety of different approaches have been developed, ranging from simple measurements to extremely sophisticated internal imaging techniques (Ellis 2000; Wells 2007b). Different models of body composition are also invoked that quantify body constituents at atomic, molecular or tissue levels (Wang, Pierson, Jr., and Heymsfield 1992).

The choice of which method to use depends on the species being investigated and the outcomes desired, as well as convenience and cost.