Animals that are fed different, nutritionally adequate, diets often grow at different rates. This is commonly attributed to differences in diet palatability (taste and smell), but there is no evidence substantiating this idea. An alternative hypothesis is that diets that promote overeating do so by minimizing the osmotic pressure (pressure exerted by dissolved substances) in the digestive tract following a meal. Dr. Ramirez will test these explanations in a series of experiments, most of which focus on the overeating induced by feeding liquid diets. The relative palatability of several diets will be compared with their ability to stimulate food intake. In another experiment, the palatability of liquid and solid diets will be altered by the addition of palatable and unpalatable flavors. The ability of the flavored diets to alter caloric intake will then be determined. The role of the pressure exerted by dissolved substances in the digestive tract will be examined by measuring it in rats that have ingested either liquid or solid meals. This pressure will also be manipulated by providing rats with foods that exert different osmotic pressures and forcing the animals to drink extra water with their meals. Additional experiments will examine the suggestion that young and mature rats respond differently to liquid diets. These studies will provide information concerning the basic mechanisms controlling food intake and how different foods influence these mechanisms. This in turn may provide practical insights into how to modulate domestic-animal growth and human appetite.
