Durk Pearson & Sandy Shaw’s®
Life Extension NewsTM
Volume 15 No. 8 • December 2012

Filling Your Brain’s Fuel Tank with More Willpower

Willpower or self-control is an energy consuming process that allows the brain to override certain thoughts, impulses, urges, and emotions in order to promote the achievement of more highly desired goals. Not surprisingly, there is only a limited amount of energy available for the process and recent research shows that the use of willpower for one act of self-control impairs available willpower for a subsequent attempt at self-control.1 Understanding how this works will help in economizing the use of willpower for more efficient use or, even better, increasing the amount of available willpower.

We describe here some experimental results reported in one paper1 on the neurological basis of willpower, but there have been quite a number along the same line (see citations in paper #1). Included is proof of causation—that the brain’s glucose supply is the source of energy supporting the willpower program. You, too, can have more willpower when you need it—it could be as simple as drinking 140 calories of a glucose-laden glass of lemonade. Read on.

Limited Amount of Self-Control is Available

The researchers begin by supporting their contention that, consistent with evidence from many different scientists, self-control requires an energy source and that, under conditions where that energy has been depleted by prior effortful self-control, it becomes more difficult to generate more self-control. For instance, they cite1 studies in which using self-control to resist the temptation to engage in a certain behavior results in an impairment in resisting a subsequent behavior, such as suppressing stereotypes and prejudice, coping with thoughts and fears of dying, controlling one’s monetary spending, resisting binge eating of palatable foods or drinking alcohol, restraining aggression, and others.

The brain depends upon glucose as its main fuel. The researchers1 note that “most cognitive processes are relatively unaffected by subtle or minor fluctuations in glucose levels within the normal or healthy range” but that “[c]ontrolled, effortful processes that rely on executive functions, however, are unlike most other cognitive processes in that they seem highly susceptible to normal fluctuations of glucose.” For example, they note that one type of task requiring effortful cognition is the Stroop test, where a word naming a color is printed in a different color than that named by the word, so that when one is asked to name the color shown it requires effortful decision-making. Low glucose has been associated with impaired performance on the Stroop test, that is it takes more time to name the color and more errors are made in doing so than on an easy test such as looking at a blob of color and having to name the color. Another example of a difficult test that depletes glucose is a driving simulation task.

First, the researchers established that blood glucose levels are reduced from before to after performance of an initial self-control task and that this led to poorer performance in a subsequent self-control task. One such study involved requiring that participants watch a 6 minute video of a woman talking (without sound) and, to induce a need for self-control, requiring that those watching not look at captions at the bottom while she was talking. Another group of participants just watched the video without any constraints on where they looked. The result showed that, indeed, blood glucose was significantly reduced in those watching the video but having to avoid reading captions. Blood glucose did not differ between the before and after state in those just watching the video without constraints. “Thus, all participants watched the same video, but glucose levels dropped only among participants who had to exert self-control while watching.”1

Another task performed by volunteers was the Stroop test. Glucose levels at the start of the experiment did not predict the performance (speed of identifying color and errors made), but lower glucose after having watched the video and not looked at captions (as described in the paragraph above) was associated with poorer Stroop performance; those subjects were significantly slower in identifying colors and they did make more errors, but the increased number of errors did not reach significance.

Enhanced Self-Control With Glucose

The most interesting part of the study occurred when the researchers tested their hypothesis that if depleting a source of energy (by reducing the level of blood glucose) results in impairment of self-control, then replacing the energy source should restore self-control at least in part back toward its initial level. Participants started out by performing 20 Stroop trials. Then half watched the video as mentioned above, having to avoid looking at the captions. The other half just watched the video without any constraints on where they looked. Following that, they were given 14 ounces of lemonade (containing either 0 calories because it was sweetened with Splenda or 140 calories because it was sweetened with 35 grams of glucose). The subjects were given some questionnaires to fill out but were not told that this was to allow time for the glucose to be absorbed and reach the brain from the bloodstream. Finally, they did 80 Stroop trials and were evaluated for speed and accuracy.

The results showed that those who watched the video with the self-control condition (don’t look at the captions) and received the glucose containing drink didn’t make additional errors like those who watched the video in the self-control condition but received the placebo drink. (In this part of the study, the number of errors made in the Stroop test was more sensitive to the effects of glucose than the speed of identifying colors.

In the researchers’ discussion of the results, they said, “At its core, self-regulatory change involves overriding one response in order to enable a different response. The stronger the initial response or impulse, the more difficult the self-control task will be—and, we would assume, the greater amount of energy in the form of blood glucose the system would have to expend in order to succeed.”1 We agree with the researchers that glucose is likely to provide only a short-term help in counteracting the performance impairment resulting from prior effortful self-control because there will be counteracting metabolic factors (such as the need to release insulin in order to be able to use the glucose for energy) that prevent maintaining a high level of energy from a given amount of glucose for very long. It would be like trying to maintain the energy increasing effects of caffeine by drinking a cup of coffee again and again. That doesn’t work for very long because the factors that provide the lift from caffeine, such as the release of noradrenaline, are depleted after a while. In fact, you can extend the energy enhancing effect of caffeine by taking nutrients the brain can use to make more noradrenaline, such as the amino acids phenylalanine or tyrosine.5,6 In the case of glucose, we would expect that taking nutrients along with glucose that improve insulin sensitivity, such as chocolate,2 black tea,3 or cinnamon,4 might extend the length of time you could extract energy from a given amount of glucose.


  1. Gaillot et al. Self-control relies on glucose as a limited energy source: willpower is more than a metaphor. J Pers Soc Psychol 92(2):325-36 (2007).
  2. Grassi et al. Short-term administration of dark chocolate is followed by a significant increase in insulin sensitivity and a decrease in blood pressure in healthy persons. Am J Clin Nutr 81:611-4 (2005).
  3. Cameron et al. Black tea polyphenols mimic insulin/insulin-like growth factor-1 signalling to the longevity factor FOXO1a. Aging Cell 7:69-77 (2008).
  4. Couturier et al. Cinnamon improves insulin sensitivity and alters the body composition in an animal model of the metabolic syndrome. Arch Biochem Biophys 501:158-61 (2010).
  5. Borison et al. Metabolism of an antidepressant amino acid. presented in poster session at April 9-14 1978 FASEB, Atlantic City, NJ [l-phenylalanine in the treatment of depression].
  6. Gelenberg et al. Tyrosine for the treatment of depression. Am J Psychiatry 137(5):622-3 (1980).

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