Obesity and anorexia as neuroendocrine disorders.

Expression of appetite or the motivational drive toward an energy source is a highly regulated phenomenon in vertebrates. In humans, energy intake is not influenced solely by nutritional needs but also by emotional, social and cultural factors; however, over the long-term the cumulative match between energy expenditure and energy intake is tuned with high precision (Edholm, 1977). This phenomenon reflects an active regulatory process, termed energy homeostasis, that promotes stability in the amount of body energy stored in the form of fat, and it is considered essential for rigidly guarding the body weight around a set point. Abnormalities in the onset, periodicity, duration and magnitude of eating episodes generally underlie augmented appetite (Stunkard, 1996; Bray et al., 1990). Increased appetite, whether temporary, as seen clinically in transient bingeing, or permanent, invariably culminates in an increased rate of body weight gain and obesity (Kalra, 1997; Wadden, 1993; Perri et al., 1993; Bray, 1996). On the other hand, anorexia due to psychobiological causes (Stewart-Agras et al., 1984; Crisp, 1984) or in response to acute and chronic infections, inflammation and trauma is followed by severe loss of body weight (Moldawer et al., 1988; Plata-Salaman et al., 1991; Grunfeld et al., 1992).