Blood Glucose Patterns and the Control of Feeding Behavior: A New Framework for the Control of Meal Initiation

Abstract

A new framework for understanding the control of feeding behavior, with special emphasis on the evolution of hunger, the initiation of feeding, and its dependence on patterns of blood glucose, is the subject of this chapter. A perspective on the current status and future directions of this search for a more complete understanding of the regulation of feeding behavior in laboratory rats and humans is presented, including theoretical and experimental components. Experimental evidence supports the hypothesis that spontaneous, self-resolving transient declines in blood glucose precede and signal meal initiation in nondeprived, free-feeding rats and time-isolated humans. This signal precedes food-seeking behavior and the initiation of a meal but does not predict the size of the meal or the timing of meal termination. The precise antecedent conditions required, in terms of the shape of the transient declines in blood glucose, for meal initiation or meal requests have been defined. This is followed by a statement and overview of a signal detection and pattern recognition theory of the control of meal initiation. The current working hypothesis that transient declines in blood glucose are endogenous metabolic patterns that are represented in the central nervous system is then presented. These patterns are detected and recognized by the central nervous system and are mapped into meal initiation in rats and are correlated with meal requests in humans. The distinguishing feature of the theory is that it is the temporal pattern, shape, or waveform of blood glucose dynamics – rather than the glucose molecule, or the absolute decrease in blood glucose, or blood glucose concentration, or glucose utilization – that is detected and contains critical information that is extracted by the central nervous system to control meal initiation. Then, the experimental studies on meal initiation and its dependence on patterns of blood glucose in humans are reviewed. An association between transient declines in blood glucose concentration and meal requests and changes in hunger ratings in human subjects isolated from food and time cues has been demonstrated. This association was observed following both spontaneous and insulin-induced transient declines in blood glucose. These results support and strengthen the conclusion that the transient decline in blood glucose represents a temporal pattern that reflects an antecedent physiological event or provides a signal related to the expression of hunger in humans. Finally, the implications for the understanding of the control of feeding behavior and the regulation of energy balance are discussed.