The other day, I went for a run on my lunch break. This is something I try to do regularly, but the reality is I can rarely pry myself away from my desk. So I was proud of myself for having finally gotten a run in. When I came back from the run, I did something else I rarely do . . . I ordered french fries. I usually avoid french fries like the plague. But in the afterglow of my healthy run, I threw my normal dietary prudence to the wind and said, “what the heck!”
Repeatedly on this blog, I have cited Roy Baumeister’s research on willpower, saying willpower is “like a muscle” in that it can be strengthened with practice, but it can be depleted with overuse (see here, here and here.) By using my willpower to go for a run, I depleted it, and when I came back for lunch, I couldn’t resist the french fries.
Not only does this theory seem to align with my personal experience, but Baumeister is one of the most widely respected and cited psychologists in the biz, and his research is pretty strong, showing again and again (over 100 papers and a bestselling book) how our willpower can be depleted.
Recently, however, there has been substantial controversy over key aspects of Baumeister’s theory: for example, that glucose levels (blood sugar) is a key factor in self-control. According to Baumeister, when our sugar levels are low (glucose depletion) our self-control is weakened (the reason that diets are doomed to failure.) And when our willpower is depleted, a nice tall glass of sugary lemonade can refill the tank
Several scientists have been questioning this theory, and some have begun to punch holes in it.
Evolutionary psychologist, Robert Kurzban, for example, has long felt that this glucose theory was improbable:
Consider that the entire brain uses about .25 calories per minute. If we suppose that the “self-control” task increases overall brain metabolism by 10%—a very large estimate—then the brains of subjects who do one of these tasks for five minutes, who are categorized as “depleted,” have consumed an extra 0.125 calories. Does it seem right that you need 100 calories from lemonade to compensate for a tenth of a Tic Tac?
And that’s not all that doesn’t add up. Kurzban also points out that exercise, “which consumes orders of magnitude more of glucose,” doesn’t deplete willpower at all. In fact, it seems to strengthen it (my afternoon run experience to the contrary.) For more on this, see Kurzban’s book, “Why Everyone (Else) Is a Hypocrite: Evolution and the Modular Mind.”
And Kurzban isn’t the only psychology professor to challenge Baumeister’s ideas. Last year, Carol Dweck (of “Mindset” fame) and Greg Walton of Stanford University published research suggesting that willpower is only limited if you believe it is. In other words, your attitude about self-control is more important than the sugar level in your blood, or even how exhausted your willpower “muscles” are.
Other research suggests that self-control is less depleting if it is autonomous. And that mindfulness can serve as an unlimitable source of energy that helps to fuel willpower on an ongoing basis.
According to Dweck and Walton, “Messages suggesting that willpower is severely limited and that we need constant sugar boosts” will only serve “to further inflate the American waistline and hinder our ability to achieve our goals.”
In an article earlier this year, Kurzban cited research by Daniel Molden and others showing that willpower could be replenished by simply swishing a sugary beverage around in the mouth. It appears that the taste of sugar might activate a reward center in the brain, providing an incentive for increased self-control. They also verified that the sugary mouthwash had no effect on blood glucose levels, further discrediting the theory.
A new image of willpower is beginning to emerge, not as a physiological reservoir that gets depleted and replenished throughout the day, but as a cognitive resource that is driven by our personal motivations and where we focus our attention. Just last month, two more researchers suggested that “self-control may not be a limited resource after all.”
They suggest that exercising our willpower does not deplete it or weaken it, as Baumeister proposed. But exercising our willpower changes our motivation, making us feel more justified in indulging.
Other scientists, however, are rising to Baumeister’s defense. According to neuroscientist Bernard Baars, citing brain studies of Duncan and Owen, measuring blood glucose levels is not the right way to assess the glucose impact on self-control. You would have to measure glucose in the frontal lobe of the brain, which would have very little correlation with the blood glucose in the body.
Perhaps this whole debate is a false dichotomy. It may be that both theories are correct, i.e. that willpower is a depletable resource but there are motivational factors that can boost flagging reserves (isn’t this true with all of our depletable resources?)
From a real-world standpoint, this seems like it may be more of a semantic difference than a practical one. Did I indulge in french fries after my run because my willpower had been depleted or because my motivation had changed? Does it really matter? And could I have strengthened my resolve by popping a lifesaver into my mouth? Maybe. And would that have been because it boosted my glucose level or because it triggered a reward center in my brain? Does it matter?
On one level, it does matter. Because if we understand how the mechanism works, we can use it to our advantage. I happen to like Baumeister’s “like a muscle” analogy. It is easy to explain and easy to relate to. But that being said, there is a lesson to be learned about the nature of science. Science, and especially psychology, is inexact. The images we get about human behavior can be helpful but they are out-of-focus. Theories are exactly that . . . theories–even when they’ve been tested. And as for willpower . . . well I guess we’re not really sure yet how that works.
References and recommended reading:
Baumeiser, R. F. & Tierney, J. (2012). Willpower: Rediscovering the Greatest Human Strength. Penguin Books.
Kurzban, R. (2012). Why Everyone (Else) Is a Hypocrite: Evolution and the Modular Mind. Princeton University Press.