Willpower Revisited: Scientists Disagree

Day 10: Super Size Me
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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.

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Evolutionary psychologist, Robert Kurzban, for example, has long felt that this glucose theory was improbable:Tribute To Guitarist Pat Martino - Scan/Edit 03 07

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.

14/365... Haters!!
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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.

18 Responses to Willpower Revisited: Scientists Disagree

  1. Nicholas Ritchey October 2, 2012 at 7:13 pm #

    Hi Jeremy,

    Tony Schwartz talks about Baumeister’s work in “Be Excellent At Anything” (awesome read btw), but doesn’t go into the mechanism you mentioned (glucose).

    I regularly deplete my muscle glycogen due to my training (powerlifting) and literally feel my brain competing with my body for glucose… the mental lethargy is ridiculous. But that’s completely different from having a stressful day or practicing self-restraint… in no way are the two even remotely close in intensity.

    I don’t know if Baumeister has gone much into sleep, but I’d suspect sleep deprivation, elevated cortisol and lack of conscious renewal during the day to impact willpower far more than this small depletion of glucose from a minuscule caloric increase in activity by the brain.

    Does willpower get depleted by “contracting” it for too long… sure, but can it be renewed through meditation, napping, a 30 minute walk, or doing some other restorative activity? Definitely.

    And this is where nutrition gets tricky. Even suggesting a sugary drink is flawed because you’ll have an insulin spike followed by an energy dip which will likely decrease willpower later… and you’re getting more calories.

    If you wanted to cover the glucose issue without the post-sugary energy dip, you could recommend a ketogenic diet where glucose is continuously provided by fat cells through gluconeogenesis. This may not be practical for everyone, but provides sustained energy to the brain even in endurance athletes because your fat stores are roughly 20x larger than your muscle glycogen stores.

    There’s a kink in the willpower as a muscle armor, but that doesn’t mean it’s completely broken. While sugary spikes may be too short-minded and keto-adaptation a bit extreme, active renewal in the form of napping/meditation/walking/etc. may be very practical solutions.

    So feel free to keep talking about willpower as a muscle… just don’t put too much stock in a questionable mechanism of action. 🙂

  2. Marie-Josee Shaar October 2, 2012 at 11:49 pm #

    Very, very interesting article, Jeremy! And very, very important topic! If we could understand how to really boost self-regulation, then we could save a lot of people from themselves! That’s my line of biz, so you’ll see that I’ve thought of the question long and hard! 😉

    Here’s my hypothesis – and you might like to know that I suggested it to Baumeister a while ago. He said he liked it, that it was quite possible, but that he didn’t know of any research on it. Hopefully some researcher reads this and probes further!

    I think that a possible connection is not blood sugar level, but serotonin. And this connection would resolve a lot of the discrepancies you are noting above:

    – Serotonin is known to help us regulate our behaviors (which ones isn’t fully clear, but we know it helps with sleep, food, mood and possibly also exercise – the ones that really matter, at least to me!)

    – Consuming any form of carbohydrates facilitates the production of serotonin. So it may not be the sugar in the lemonade per se that caused the rise in self-regulation; it could be the serotonin (now we’d have to see if there was enough time elapsed between the glass of lemonade and the 2nd attempts at self-regulation for an increase in serotonin to occur, but even if there isn’t, serotonin could still be at play – keep reading).

    – Exercise also increases serotonin levels, so we’d have Kurzban’s objection covered.

    – Dweck says that the growth mindset is associated with greater self-confidence, resilience and positive emotions, whereas the fixed mindset is associated with greater anxiety, stress and self-depreciation. The first would lead to someone having higher serotonin levels; the second, higher cortisol. Again, serotonin might be part of the equation. (Now of course we have different mindsets for different things, but it could be possible that while we are interacting with an environment where our mindset is mainly fixed, serotonin decreases, and while in an environment where our mindset is mainly growth, serotonin is on the rise – thus confirming Dweck’s findings that those who think they can self-regulate, can)

    – Molden’s research about the reward center in the brain would also fit in with my hypothesis. Serotonin is also associated with reward centers. But we’d have to look deeper to see if we’re looking at the same centers in both cases.

    So – thoughts, anyone?
    Looking forward to the debate!


  3. Jeremy McCarthy October 3, 2012 at 8:17 am #

    Thanks Nick and MJ, I think both of your thoughts definitely add something to this discussion. I know a few people have said that meditation replenishes self-control which is interesting if validated (I haven’t seen the research on this) because I see meditation as a self-control exercise which should deplete it in the short term and strengthen it in the long term per Baumeister’s theory. MJ, I have heard you speak about Serotonin before and so I think you are definitely on to something.

    I do need to clarify one thing. Baumeister does not suggest drinking a glass of sugary lemonade to boost your self-control (although I implied that in the article.) It is only for research purposes that getting a quick spike of glucose is the easiest way to measure the impact of a quick does of glucose on self-control in the lab.

    I’m with Nick that the muscle analogy still works AND there are other motivational factors at play. Nick, I’m sure you can attest to the fact that a depleted muscle can also suddenly regain strength when the right motivational cues are in place.

    Thanks for contributing to the discussion. I really think self-control underpins so much of what we want in life. It drives everything from personal responsibility and lifestyle changes, to altruism and moral behavior. I can think of few things more important.

  4. Marie-Josee Shaar October 3, 2012 at 9:06 am #

    Oh! What a great point, Nick! Of course, sleep and meditation are huge to replenish self-regulation! And both increase serotonin levels, so my hypothesis may still work!

    Like you both, I also think the muscle analogy is still useful – let’s not throw the baby out with the bath water! 😉


  5. Amit Amin October 3, 2012 at 12:09 pm #

    I’ve been wondering the same things as you… first I read his great book on willpower, and then I read some of the newer studies you referenced.

    “Because if we understand how the mechanism works, we can use it to our advantage.”

    I think that’s a bit of an understatement. Behavior modification shouldn’t be so hard – there’s no underlying principle of the universe that requires that doing what we logically (or not so logically) decide to do should be so much harder than what our body wants us to do. The first problem is that we don’t even really understand why it’s so difficult.

    Personally, I’ve found most utility from a dopamine theory of motivation – when my motivation is lacking I do whatever I can to drum up my desire (laughing, gargling sugar water, looking at images of sexy women, going for a jog, listening to awesome music, etc…). It always works.

    Ironically, the failure point is that I often lack the motivation to motivate myself.

  6. Marie-Josee Shaar October 3, 2012 at 12:33 pm #

    I thought of dopamine too, Amit! Except that dopamine production isn’t boosted with carbs… That’s why I’ve been thinking that serotonin might be the link instead. But hey! I’m happy to see that somebody else has been thinking along the same lines as my hypothesis!


  7. Jeremy McCarthy October 3, 2012 at 3:20 pm #

    I loved your last sentence Amit. Nick Ritchey (also on this thread) has written on this blog about Kaizen, a great solution for getting over the problem that half the battle seems to be taking the first step. If you make the first step easy enough, you get started and then momentum kicks in from there.

    The question is, how do you want what you want to want? I wrote about that here: http://positivepsychologynews.com/news/jeremy-mccarthy/2012060522562.

  8. Oz October 4, 2012 at 6:14 am #

    Dwecks research is flawed – effect doesn’t last after repetition of willpower task

    hers is a classic example of poorly designed research

    By the way meditation increases willpower – but same flaw as dwecks work

    See http://www.innate-intelligence.com.au/blog/?p=953

    Anyhow back Into the troll cave to ponder more negativity

  9. Oz October 8, 2012 at 5:05 pm #

    Jeremy – out of interest why didn’t you cover the research countering dwecks claims – we both were alerted to it by jazi on the list serve

  10. Jeremy McCarthy October 8, 2012 at 8:47 pm #

    I must’ve missed it. What did it say? The study that you cite above is interesting because I’m assuming the meditation practice also required the use of self-control. So theoretically, they should be more depleted not less. Why do you think the meditation replenishes it?

  11. Oz October 9, 2012 at 3:44 am #

    This study https://www.carlsonschool.umn.edu/assets/166691.pdf

    Why does exercise increase stamina?

    Back to the cave to meditate

  12. Jeremy McCarthy October 9, 2012 at 9:52 am #

    Exercise increases stamina in the long-term but depletes it in the short-term. It doesn’t surprise me at all that meditation would increase willpower over the long term, it seems surprising that it would increase it in the moment. That seems to contradict Baumeister’s theory.

  13. Jeremy McCarthy October 9, 2012 at 9:57 am #

    You’re right, I should have included that article . . . it pretty much sums it up. Motivation and depletion are both important. And the “like a muscle” analogy still works well since muscle depletion can also be overcome (to a limit) by self-efficacy and motivation.

  14. Oz October 9, 2012 at 4:03 pm #

    Key line is this

    The bold claim that ego depletion is “all in your head” (Job et al., 2010) however should be tempered with the recognition that sub- jective beliefs and motivations are most efficacious when depletion is mild or incipient. Subjective beliefs in unlimited willpower did in fact improve performance among the slightly depleted. Among the severely depleted, however, those beliefs had no effect — if anything, they had the opposite effect.

    Ie wishful thinking only gets you so far

    Rememember the meditation study has the same flaw as dwecks – proves nothing

  15. Sun Abdullah October 31, 2012 at 1:38 am #

    Very good article indeed, i agreethat someone need to not discourage and ever lose interest in his goals, anyway.

  16. Aaron November 17, 2012 at 2:02 am #

    “Theories are exactly that . . . theories–even when they’ve been tested. ”

    Please stop using “Theory” as something that has no significant meaning.
    A Theory is what happens after it goes through intensive scrutiny and its proven.
    When you are testing something out it is called a “Hypothesis”.

    I don’t mind personally, but your enforcing the idea that Theories are weak, so when people hear “Theory of Gravity” and “Theory of Evolution” they think they are just being tested and aren’t yet proved. This really hurts science in general.

  17. Jeremy McCarthy November 17, 2012 at 8:20 am #

    Thanks Aaron, I appreciate your criticism and I agree with your point. Believe me, I LOVE science and that is why I have spent the last 2 and a half years on this blog talking about and sharing the “theories” of positive psychology. But while I think we should all value and appreciate science, the average layperson’s (not the scientist’s) bias is to misconstrue science as fact and evidence as proof.

    What you are seeing in my comments is my own bias based on seeing a constant barrage of criticisms of positive psychology based on:
    1. Limitations of the research.
    2. Contradicting or competing theories and evidence.
    3. The tendency of the media to overreport or “overpromise” the benefits of positive psychology.

    These are all valid criticisms, particularly if you are expecting science to provide “facts” and “proof.” But if we recognize that science is primarily about providing evidence for theories then we take these theories with an appropriate grain of salt, we appreciate whatever evidence we have rather than focusing on the limitations of every piece of research, and we don’t get caught up in a bunch of hype every time a competing theory is introduced or an existing theory gets debunked.


  1. Self-Control at the Intersection of Eastern/Western Thought | The Psychology of Wellbeing - November 6, 2012

    […] One research domain, in particular, that has garnered significant attention recently in positive psychology is around “willpower” a.k.a. “self-control” or “self-regulation”.  (See books on the subject below, and it has also been a regular subject of this blog.) […]

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