SPOILER ALERT!
Self-control (willpower) requires energy.
This energy source is not unlimited
Glucose from foods is the source of energy for willpower
Low glucose = poor willpower
Poor willpower leads to poor emotion regulation, including low frustration, high irritability and poor coping with stress.
Research shows that effortful self-regulation or willpower relies on a limited resource that operates like a strength or energy. There is a variety of situations where self-control is vital for optimal functioning in the interpersonal and social spheres, and for example we often need to control our thoughts, emotions, desires, and behaviors. By exerting self-control, we rein in on our impulses and avoid putting ourselves in harm’s way.
Self-control is limited
Despite the obvious benefits of self-control, we frequently give in to our impulses, and as a result we may take up smoking, eat junk foods and perform many other behaviors that we always end up regretting. Research attributes these lapses in self-control to its finite energy source, which means that unlike the Energizer batteries, willpower does not “keep going and going…”
Subsequent investigations into its energy source highlight the role of glucose in the maintenance of willpower. Glucose is the almost exclusive fuel for the brain by enabling effective cerebral activity, and it can be consumed faster than it is replenished. In addition, glucose depletion (reduced glucose) produces conspicuous cognitive and behavioral deficits, such as amnesia, confusion, anxiety, blurred vision, and bizarre behavior and personality changes.
The link between blood glucose and self-control
Likewise, studies also associate low blood glucose with failures of self-control, which suggests that when glucose levels are low, it is harder to exert self-control. For example, a few studies report that hypoglycemia (i.e., low blood glucose) is linked with loss of attention and poor concentration, which reflects impaired willpower since the control of attention is exerted through willpower.
Similarly, emotion regulation relies on self-control and, depending on the energy level that is available, results in the suppression (i.e., high energy level) or the amplification of emotions (i.e., low energy level). Notably, several studies found that during low glucose periods, people are more likely to report feeling anxiety, irritability, and other bad moods compared to when glucose is high.
Furthermore, other studies consistently draw the same parallel between low blood glucose levels and impaired self-control by implicating low blood glucose levels in aggressive behaviors, smoking, poor coping with stress, sexual promiscuity, and other reckless behaviors. Particularly pertinent is the frequency of reckless behaviors and other behaviors related to impaired self-control in the evening and later in the night compared to the morning, which correspond to times of depleted glucose levels.
Reference:
Gailliot MT, Baumeister RF. The physiology of willpower: linking blood glucose to self-control. Pers Soc Psychol Rev. 2007 Nov;11(4):303-27. doi: 10.1177/1088868307303030. PMID: 18453466.