The psychobiology of meals

Meals are considered as bouts of behavior that, although necessary for supplying nutrients to the body, result in undesirable perturbations of homeostatically controlled parameters. If the environment dictates that an animal mainly eat very large meals, these meal-associated perturbations become potentially dangerous. When the opportunity to eat a very large meal is regular and predictable, animals adopt strategies that maximize the efficiency of the process while minimizing the threatening homeostatic disturbances. Hence, prior to the onset of meals, animals elevate their body temperatures, presumably to facilitate critical processes involved in ingestion and/or digestion. Temperature continues to rise during the meal, and as it approaches potentially dangerous levels, the meal is terminated and temperature falls to "safer" levels. Animals also undergo a slow decline of blood glucose prior to the initiation of meals, thus minimizing the postprandial elevation of blood glucose caused by the absorption of ingested carbohydrates. Analogously, prior to meals, animals undergo a decrease of metabolic rate, thus precluding the necessity for postprandial increases of metabolic rate to reach even higher absolute levels. These premeal changes of regulated parameters have been interpreted by others as indicating depletion of one or more energy supplies so that the animal is compelled to eat. Contrary to this, we interpret the changes as ones that enable the animal to prepare adequately to consume a large meal when the environment is predictable.