The value of fat deposition and oxidation may be interpreted in terms of its effects rather than its causes (Tinbergen 1963). By convention, it is common for biomedical researchers to focus on adipose tissue as a physical substance. Strictly speaking, however, natural selection acts most strongly on life cycles (Bonner 1965) and strategies (Houston and McNamara 1999), and in this case the relevant strategy is the capacity both to deposit energy in adipose tissue and to release it as required. This point was explicitly made by Pond (1998), who distinguished between the functions of fattening and the functions of fat.

In Tinbergen's original approach (1963), the focus was on survival value. Since his pioneering article was published, biologists have incorporated a broader approach to assessing the value of a given trait or strategy. Traits are best assessed in terms of their total contribution to genetic fitness rather than to the mere survival of the organism (Williams 1966). Human fatness plays important roles in reproductive fitness and sexual selection, including trans-generational transfers of energy, and these components of evolutionary biology must therefore be incorporated into assessments of function. Furthermore, adipose tissue is increasingly recognized to play a sophisticated role in the regulation of competing functions, as well as providing the energy required for them.

Buffering famine and malnutrition

The fat content of adipose tissue represents an energy store, and its most basic function is to buffer against fluctuations in dietary energy supply.