and Resistance to Obesity
CYNTHIA M. BULIK
DAVID B. ALLISON
In the wake of unprecedented economic growth; decreased infectious disease; nearly unlimited food supply; wide availability of high-fat, highly palatable, and preprepared foods; large portion sizes; and technological advances leading to a more sedentary lifestyle, modern westernized environments promote obesity (see Chapter 78). Despite the increasing prevalence of obesity, some individuals remain thin. In this chapter, we explore evidence supporting the study of constitutional thinness as a complementary and informative strategy for understanding the development and maintenance of obesity.
Throughout human evolution, selection pressures may have favored efficient energy storage and moderate adiposity (see Chapter 83). Such traits would increase the chances of survival during periods of famine or exposure to the elements. Conversely, traits producing inefficient energy storage or high metabolism, which would resist weight gain and fat storage, may have been selected against, and via natural selection, may be relatively rare. A comprehensive understanding of individuals who remain thin in the presence of strong environmental factors may assist with preventing individuals who are genetically predisposed from becoming obese and, ultimately, with the development of effective treatments for obesity.
It is unclear whether thinness represents a distinct phenotype or merely the lower tail of the body mass index (BMI) distribution. Several factors must be considered. In order to