Psychological scientists X.T. Wang and Robert D. Dvorak from the University of South Dakota looked into how blood glucose levels affect our thinking about present and future rewards.
Participants in the study answered a series of questions asking if they would prefer to receive a certain amount of money tomorrow or a larger amount of money at a later date. The subjects answered seven of these questions before and after drinking either a regular soda that contained containing sugar or a diet soda, which contained the artificial sweetener aspartame. Blood glucose levels were measured at the beginning of the experiment and after the participants drank the soda.
It was seen that blood glucose levels might influence people's preferences for current versus later rewards. The volunteers who drank the regular sodas and thus had higher blood glucose levels were more likely to select receiving more money at a later date, while those who had diet sodas and had lower blood glucose levels were likely to opt for receiving smaller sums of money immediately.
These findings suggest an adaptive mechanism linking decision making to metabolic cues, like blood sugar levels.
The results show that when we have more energy available (higher blood glucose levels), we are likely to be more future-oriented. The authors of the study write, "the future is more abstract than the present and thus may require more energy to process. Blood glucose as brain fuel would strengthen effortful cognitive processing for future events."
On the other hand, having low energy (low blood glucose levels) may make an individual focus more on the present. It can also be said that artificial sweeteners may alarm the body of imminent caloric crisis, causing increased impulsivity.
The authors conclude that if controlling blood glucose levels may influence our decisions for later versus current rewards, then "reducing the degree of fluctuation in blood glucose may offer a possible means for the treatment and intervention of some impulsive disorders, anorexia, drug addiction, and gambling addiction."
The findings of the study have appeared in Psychological Science, a journal of the Association for Psychological Science.