Differential effects of ingestion and taste of glucose on self-control and intertemporal decision makin

Two conflicting theories of the interaction between human decision-making and glucose exist within the literature. One theory, the Strength Model (Gailliot & Baumeister, 2007), posits that cognitive tasks deplete blood glucose resources, while an alternative theory focuses on motivational effects of glucose administration on self-control (Chambers, Bridge, & Jones, 2009). Despite the intensive empirical debate, a third theory exists that may bridge the divide between the two conflicting theories. This study sought to integrate motivation and depletion theory through signal theory (Wang & Dvorak, 2010), rooted in evolutionary psychological theory, positing that the taste of glucose acts as a signal of impending body energy budget increases, elevating motivation and self-control while actual ingestion of glucose forecasts resource surplus and conservation and leads to a greater future orientation and reduced delay discounting. This study empirically assessed the impact of both the taste of glucose and changes in blood glucose levels on self-control and intertemporal decision-making through a 3 (between-subject metabolic manipulations) x2 (within-subject self-control vs. an intertemporal choice task) design, consisting of a glucose ingestion group (glucose consumption with a significant increase in blood glucose levels), a glucose rinse-and-spit group (taste of sugar with no increase in blood glucose), and a control group of water consumption (no taste of sugar and no increase in blood glucose). The participants were given both a self-control task (a grip maintenance task with a dynamometer) and a task of intertemporal choice between a smaller-and-sooner reward and a larger-and-later reward, before and after the manipulation. Results demonstrated that taste of glucose increased self-control (accuracy scores in grip control) and increased delay discounting, as measured in the intertemporal choice task. In contrast, actual ingestion of glucose strengthened self-control and significantly reduced delay discounting. These results differentiated the effects of sweet taste and actual ingestion of glucose on self-control and delay discounting in intertemporal choice, supporting the Signaling hypothesis of glucose, integrating both motivational and resource strengthening effects of glucose on self-control and intertemporal decision making. These differential effects of glucose taste and glucose ingestion offer useful implications for interventions of impulsive behaviors and for self-control and self-regulation.