Neuroendocrine aspects of the control of eating in eating disorders

Because most eating is organized as meals, the principal questions for eating research are: when are meals initiated, what foods are chosen, and how much is eaten. Individual experience undoubtedly explains much or most of human eating. In addition, however, unlearned physiological processes contribute, and form the basis for much of what is learned. These physiological processes include hunger, satiety and food reward (or, hedonic, palatability) processes. We emphasize peripheral, sensory signals in the controls of eating because several of them are well understood and because they provide a way into the analysis of brain function. Such signals include palatability stimuli as well as signals arising from gastrointestinal (GI) and metabolic processes. These signals reach the brain via both hormonal and neural pathways. Peripheral controls can be divided into within-meal signals, which affect eating during the same meal that elicits the signal, and across-meal signals, which affect eating in later meals. The slowest feedback signals are adiposity signals, which are eating controls related to body fat content (1, 2). We review evidence that in patients with ED there are disturbances in each of these types of signals. The normally close relationship between eating behavior and eating-related subjective experiences suggests that these phenomena have common neurological foundations. With respect to ED patients, however, even the more physiological aspects of eatingrelated subjective experiences are often disturbed. For example, ED patients’ ratings of the intensity of hunger and satiety may not show the usual inverse relation (i.e., satiety increases as hunger decreases) and may not change coherently during meals (i.e., hunger may not decrease). Similarly, ratings of food reward are under unusually strong cognitive control. For example, in ED universally preferred flavors such as sweet are often reported to be unpalatable. These sorts of abnormal experiences greatly complicate the interpretation of both biological and psychological data. The application of powerful new methods, such as functional brain imaging, may help in understanding how such disordered feelings arise and what their role is in the disordered eating of ED patients.