Animal Models of Obesity

Complex physiological and behavioral conditions that occur in humans can be investigated in animal species that display, whether spontaneously or as a result of intervention, similar features of critical aspects of the condition being studied; such animals provide what is known as an animal model of the condition. In the case of obesity, the critical aspect is accumulation of excess body fat. Like humans, adequately nourished nonhuman species store body fat in amounts that support growth and reproduction; the percent of body weight that is due to fat at a given age may be quite consistent for the species despite variation in environmental conditions. However, like humans, other animal species can accumulate additional body fat (i.e., show an obese phenotype); this excessive accumulation may be associated with the behavioral and metabolic changes characteristic of human obesity.

Animal models can provide valuable information about human conditions that would be difficult or even impossible to obtain from human subjects. The shorter gestation periods and life spans of rodents, for example, make it possible to examine progression of obesity throughout life, as well as maternal effects on offspring and trends over many generations. Conditions in the animal's life, such as the composition and amount of food eaten, can be controlled and measured [Page 32]continually. Animal models make it possible, for example, to obtain tissues for study outside of the body, to use radioactivity or substances considered dangerous, to do surgery, or to implant devices in the brain, all of which can provide information crucial to understanding the condition in question. Perhaps the most exciting new use of animal models allows manipulation of the genome (the total deoxyribonucleic acid [DNA] of the organism) to uncover the roles that inherited traits play in controlling body fat accumulation and in mediating its effects.