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Willpower and Carbs: A Recipe for Success?

November 20, 2013

By Martin S. Hagger (Curtin University, Perth, Australia)

Willpower is something that makes us uniquely human and also makes us very successful in our environment. Self-control contributes to success in school, university, and the workplace, better health, cohesive social and romantic relationships, and positive well-being and quality of life. But, to err is also human, and all of us will have experienced occasions where our urges and desires get the better of us, despite our best intentions. Many of the problems people face in everyday life–such as failing to stick to a diet if trying to lose weight or succumbing to the temptation of a cigarette–stem from lapses or failure of self-control. More serious problems, too, are linked to poor self-control: Drug addiction, criminality, alcoholism, obesity, chronic illness, unwanted pregnancy, sexually-transmitted infections, and compulsive gambling.

Given that willpower promotes positive outcomes and its lack leads to social ills, social psychologists have sought to develop ways to ‘boost’ self-control when temptation strikes. A popular and well-cited recent approach is the ‘limited resource’ or strength model of self-control (Baumeister, Bratslavsky, Muraven, & Tice, 1998; Baumeister, Vohs, & Tice, 2007). Developed by Roy Baumeister and colleagues, people’s self-control is considered a sort of strength or energy which gives us the ability to control our urges, desires, and impulses, but is limited so only allows us sufficient willpower for a finite period of time. After exerting self-control for a while the resource becomes depleted making subsequent acts requiring self-control difficult or impossible leading to lapses. The state of reduced self-control resources was called ego-depletion.

Baumeister and many others demonstrated the ego-depletion effect using a simple but elegant experimental design, called a dual-task paradigm. In the experiments, participants would be asked to complete two consecutive tasks in different ‘domains’. For the experimental (self-control) group, both tasks would require self-control. For the control group, only the second task required self-control while the first task was usually an ‘easy’ version of the first task used in the experimental group. The self-control tasks were laboratory-based and involved the suppression of thoughts, impulses or emotions. To the extent that the performance of experimental-group participants on the second self-control task was impaired relative to the control group, the ego-depletion effect was confirmed. To date, there are over 200 dual-task paradigm experiments supporting the ego-depletion effect (Hagger, Wood, Stiff, & Chatzisarantis, 2010).

An important outstanding issue for the strength model what, exactly, becomes depleted. This has led researchers to examine possible physiological resources that might explain the ego-depletion effect. One candidate has been glucose, the primary fuel for brain function. Matthew Gailiott and colleagues tested the blood glucose levels of participants performing tasks in the dual task paradigm and noticed a drop in glucose among those engaging in self-control tasks (Gailliot et al., 2007). They surmised that this was indicative of the high demands that self-control tasks placed on energy demands and suggested that this was an analogue for the self-control resource. Intriguingly, they also demonstrated that giving people a glucose drink also improved self-control, suggesting that glucose supplementation improved willpower (Gailliot et al., 2007; Gailliot, Peruche, Plant, & Baumeister, 2009).

The role of glucose as an explanation for ego-depletion has been criticised mainly because blood glucose does not reflect brain glucose levels and the demand for glucose by self-control tasks in the brain is relatively small (Beedie & Lane, 2011; Kurzban, 2010). Researchers have suggested that the ego-depletion effect may be caused by other mechanisms such as the ability to appropriately allocate resources (Beedie & Lane, 2011). In response to these challenges, we proposed that promoting self-control by drinking glucose may be one that is perceptual rather than metabolic. In other words, we thought that perhaps the tasting of glucose acted as a signal to the brain to overcome resource depletion and boost self-control capacity. This was based on research in exercise physiology which demonstrated that ‘rinsing’ the mouth with carbohydrates led to better performance in athletes running on a treadmill (J. M. Carter, Jeukendrup, & Jones, 2004). The researchers proposed that glucose assisted in overcoming fatigue by stimulating the motivational centres of the brain. We proposed that the ‘sensing’ of glucose in the mouth may be the reason why glucose supplementation promoted self-control.

To test this premise we conducted a number of experiments in which participants’ self-control resources were depleted using the dual task paradigm but, in between the two tasks, participants ‘rinsed’ their mouth with a glucose solution (Hagger & Chatzisarantis, 2013). Control group participants also rinsed their mouth but with a sweet-tasting non-nutritive artificial sweetener rather than the glucose solution. This was to ensure that our effects were not attributable to sweetness. In one experiment participants were presented with two plates of food, appetizing cookies and unappealing radishes. Participants in the experimental condition were asked to taste the radishes only and ignore the cookies. Consistent with Baumeister and colleagues’ (1998) original experiments, resisting the temptation to eat the appealing food was considered taxing of participants’ self-control. Participants then completed a handgrip strength task, which required considerable self-control to overcome the discomfort in the forearm muscles and quit. We found that participants in the experimental group that rinsed their mouths with glucose performed much more effectively on the handgrip task relative to participants in the control group who rinsed with the artificial sweetener. Rinsing with the glucose solution seemed to enhance self-control capacity and provide a resistance to depletion. We replicated this in a number of studies. Crucially, we demonstrated that the enhancing effect was exclusive to tasks requiring self control. We did this in experiments where we included a no-depletion control group, and found no glucose enhancing effects for participants who did not engage in tasks requiring self-control. Interestingly, our findings do not seem to be a ‘flash-in-the-pan’, the effect we originally proposed (Hagger, Wood, Stiff, & Chatzisarantis, 2009) has now been supported in similar research elsewhere (E. Carter & McCullough, 2013; Molden et al., 2012; Sanders, Shirk, Burgin, & Martin, 2013).

So what do these findings tell us about the nature of willpower and self-control? One possibility is that the glucose in the mouth may enhance the areas of the brain associated with motivation and better control over impulses. A study by Chambers et al. (2009) demonstrated that rinsing with carbohydrates like glucose led to increased activity in areas of the brain associated with motivation and better cognitive control. Artificial sweeteners had no such effects. It seems that there may be cells in the mouth specifically sensitive to carbohydrates, rather than sweetness alone, that may lead to the ‘sensing’ effects in the brain. One intriguing practical possibility is that these findings may provide a way to enhance motivation quickly and simply. However, there needs to be further investigations on how these substances are best administered – sugar-infused chewing gum, candy to suck in the mouth?

Author Information

Martin.HaggerMartin Hagger is John Curtin Distinguished Professor of Psychology in the School of Psychology and Speech Pathology at Curtin University, Perth. He studies  processes involved in people’s “self-regulation” of social and health behavior, including how psychological factors such as attitudes, intentions, self-control, action plans, and motives affect their behavior and what health professionals can do to change health-related behavior. His research applies social cognitive and motivational theories to understand and to intervene and change diverse health behaviors such as physical activity, eating a healthy diet, smoking cessation, alcohol reduction, anti-doping behaviors in sport, and medication adherence.


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Sanders, M. A., Shirk, S. D., Burgin, C. J., & Martin, L. L. (2013). The gargle effect: Rinsing the mouth with glucose enhances self-control Psychological Science

Image Credit: Two Metal Hands By sritangphoto, published on 13 August 2013 Stock Photo – image ID: 100192593

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