Practicing self-control consumes real energy

ResearchBlogging.orgWhen I write an article for Cognitive Daily, I follow a similar pattern nearly every time. First I carefully read the journal article I'll be discussing. Next I take a break and work on something else. Then I get myself a caffeinated beverage and some kind of sweet treat (usually it's chocolate-covered raisins but today I'm in a coffee shop having just finished a toffee almond bar). Often it won't be until ten or fifteen minutes after I've eaten that I really get into a groove with the writing. Then I write the entire post, usually for an hour or two straight, pausing only to produce the graphics and demos accompanying the story. The hard part is finished, and the final formatting, editing, and posting can be done at leisure, sometimes even while I'm working on other projects or getting the kids started on their homework.

The part that really requires self-discipline is the writing itself. Usually I disconnect the internet in my house, or even head out to a coffee shop (one of the few remaining with no internet access) to remove all possible distractions. The self-control necessary for writing is well-known, and many writers, such as the eminent lexicographer Samuel Johnson, have discussed how excruciating the writing process is for them (Johnson once said "No man but a blockhead ever wrote, except for money."). But self-control is required for many more mundane tasks as well. Try to watch this silent movie (QuickTime Required) of me reading this post while ignoring the words that flash periodically in the lower-right corner of the screen:

It's not easy, is it? It almost feels like work, just to avoid reading. While reading is a mental process too, it feels like we're expending more energy avoiding reading than we would to do the reading itself.

Maybe there's something to that feeling. Research led by Roy Baumeister has found that people who've resisted eating cookies gave up sooner on a task requiring persistence compared to those who succumbed to temptation and ate the cookies. Other research has associated low blood glucose levels with poor performance on the Stroop task -- another task that requires people to avoid reading. Is it literally true that the sugar in our blood fuels our ability to control our impulses?

Matthew Gailliot, along with Baumeister and six other researchers, asked 103 psychology students to fast for three hours before watching a video like the one I showed above. Half the students were told to ignore the words, while the rest weren't required to exercise any self-control. Blood glucose levels were measured before and after this task. The students exercising self-control had significantly lower glucose levels after watching the movie, while the other students did not. In another experiment, students performed the Stroop task after watching the movie. The students who had to resist reading the words performed significantly worse on the Stroop task; their lower blood glucose levels after watching the movie and avoiding reading seemed to impair performance.

In another experiment, a new group of 62 students watched the movie, again divided into groups who watched normally or controlled their attention by avoiding reading. Then everyone was offered a glass of Kool-aid lemonade. Half the lemonade was sweetened with sugar, while half was sweetened with Splenda, which does not affect blood glucose levels. Since glucose takes about 10 minutes to be absorbed by the brain, everyone was given a 10-minute distractor task, then given an 80-item Stroop task. Here are the results:


As you can see, when the students consumed glucose, they performed just as well on the Stroop task, whether or not they had had to exercise self-control while watching the movie. But students who didn't consume any glucose performed significantly worse on the Stroop test.

Gaillot's team repeated these experiments several times, with tasks ranging from avoiding displays of racial prejudice to dealing with thoughts about death. In each case, the results supported the idea that self-control literally relies on glucose. When blood glucose is depleted, we're less able to exert self-control. The researchers say that the brain has a limited reserve amount of glucose, which allows us to handle the initial task demanding self control, whether it be watching a movie without reading accompanying text, or avoiding fattening snacks. Once that glucose supply is depleted, self control becomes much more difficult, across an array of different tasks.

The researchers are careful to point out that consuming sugar isn't the only way to increase blood glucose levels -- it may be that eating protein bars or complex carbohydrates offers better long-term results. However, my method of using chocolate to help give me the self-discipline to write CogDaily posts has only rarely failed me, for a test period of over three years!

Gailliot, M.T., Baumeister, R.F., DeWall, C.N., Maner, J.K., Plant, E.A., Tice, D.M., Brewer, L.E., Schmeichel, B.J. (2007). Self-Control Relies on Glucose as a Limited Energy Source: Willpower Is More Than a Metaphor. Journal of Personality and Social Psychology, 92(2), 325-336. DOI: 10.1037/0022-3514.92.2.325

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another good reason to avoid fake sugar!

By Berry Zito (not verified) on 06 Mar 2008 #permalink

Looks like self-control needs an extra reagent to actually accomplish. I really need some chocolate - too many there isn't any here...

Another reason why chocolate is good for you!

I use similar tactics write, except that my glucose levels seem to need replenishing after every paragraph - at least that's what my inner brat convinces me. ;-)

Pauline Wallin, Ph.D.
Author, "Taming Your Inner Brat: A Guide for Transforming Self-defeating Behavior"

p.s. I love your blog!

Is that why I am irritable when I'm hungry (which I am right now)?

Thanks for posting about that paper! Baumeister and the people from his lab have done a lot of research on self-control and self-control failure, and I think the one you write about here is really special in connecting something that is really a higher level cognitive activity (i.e. controlling attention) to basic psychophysical variables from a psychological point of view. Of course, neuroscientists do that a lot, but what Gailliot, Baumeister et al. have analyzed is special in that the psychology part has a lot more "ecological validity" than examining people in a scanner.

BTW: I am kind of glad you tell us about how much effort it costs write all those great posts. I always marveled at how you manage to write a really good post every day and also maintain other projects like Now I know that this is hard work even for you :-)

Being supporter of the central executive theory, i am fascinated by that finding. Executive control (aka inhibition, self-control etc.) turns out to depend on glucose. I had done research which shows that most of the impulsive criminals, in fact, perform bad on the Stroop Task and other "frontal lobe" tasks. Following Baumeisters logic, maybe glucose is the key to resisting temptation? :)


Interesting study, but the main conclusion that glucose is necessary for exercising self control isn't particularly astonishing since glucose is the body's main energy source. The study just seems to be saying that if the primary goal of a task is to drive a vehicle from point A to point B, and you don't have enough fuel (i.e., glucose) to get you to point B, you won't get to point B. Had the study indicated that a particular neurotransmitter was involved in self-control (e.g., serotonin, dopamine, acetycholine), I think that would enhance the novelty of the finding.

Research led by Roy Baumeister has found that people who've resisted eating cookies gave up sooner on a task requiring persistence compared to those who succumbed to temptation and ate the cookies. Other research has associated low blood glucose levels with poor performance on the Stroop task -- another task that requires people to avoid reading. Is it literally true that the sugar in our blood fuels our ability to control our impulses?

I find this part interesting because it seems to add a (somewhat contradictory) twist to Walter Mischel's delay of gratification research (i.e., the famous marshmallow experiment ). Mischel showed that children 4-5 years old who were increasingly able to delay eating marshmallows for a specified time period, also showed increased competence (i.e., capacity to concentrate, verbal fluency, forethought, general competence) during adolescence. He also concluded that will power seems to be a product of the capacity to mentally transform unpleasant circumstances into pleasant (e.g., some children delayed gratification by imagining other favorite things).

The finding that delay of gratification as represented by the Baumeister study cited here (i.e., delay in eating cookies), is connected with giving up on a task, seems to be at odds with Mischel's finding that delay of gratification is associated with greater general competence. However, I would imagine (as Mischel might likely suggest) that this difference is one of trait vs. state personality characteristics. The Baumeister studies are probably demonstrating state qualities associated with temporary changes in glucose levels, and not state qualities of the individual (e.g., self control) as dictated by trait states such as will power as defined by the mental capacity to remove oneself from unpleasant situations.

To reduce the apparent conflict between these two studies, it would be interesting to see what happens if you repeat this study, but create a more ecologically valid situation. For example, I could imagine a two-staged experiment where you first identify participants who differ in their capacity to delay gratification (e.g., those who delay eating cookies vs. who don't delay). Then in the next one, you have them perform the Stroop task, but this time, you put a huge jug of a glucose-drink beside the participants while they perform the task. Mischel's work would suggest that those showing greater delay of gratification would perform the Stroop task better; and I think a novel result would be to show that greater delay of gratification corresponds with less glucose consumption (perhaps suggesting that ability to delay gratification/will power is due to having a glucose efficient body and brain, much like differences in the fuel efficiency of vehicles).

By Tony Jeremiah (not verified) on 07 Mar 2008 #permalink

I wrote a post on my blog last month about an article by Baumeister that really puts this study you've mentioned in the context of his research on a grand scale. In this other article by Baumeister, he discusses the concept of free will from an evolutionary standpoint. He suggests that cultural adeptness was the driving force behind human evolution, and the developing of abilities like following rules, postponing gratification, and acting morally were adaptations necessary for the formation of human societies. He suggests that the evolution of self-control was integral to humans working and living together. If this is true, he hypothesizes, it should be a biologically expensive skill. He points to the study by Galliot et al. as evidence of this--why would self-control utilize so much glucose if it were biologically unimportant? If you're interested, I summarize this other article at…

If this is true, he hypothesizes, it should be a biologically expensive skill. He points to the study by Galliot et al. as evidence of this--why would self-control utilize so much glucose if it were biologically unimportant?

A few questions concerning this...

(1) Relative to what other processes has self-control been shown to require more glucose?

(2) Presumably, individuals vary in the rate at which glucose metabolism occurs. Has there been any research comparing individual differences in glucose metabolism with self-control?

(3) In relation to question #2, might it be possible that free will/self control actually exists on a continuum consistent with a Gaussian distribution, rather than its common characterization as an all-or-none phenomenon?

(4) Shouldn't evolutionary principles imply that biologically expensive (nervous system) processes will not evolve over time (i.e., species survival would be enhanced if food and/or glucose demand decreases relative to a concomitant increase in a species' population)? I think that seems to be what happened with humans (h. sapiens) with a reduction in body size (although an increase in brain size) relative to our Neandertalis predecessors.

By Tony Jeremiah (not verified) on 07 Mar 2008 #permalink

Interesting article. How about drinking alcohol?

By winston hernandez (not verified) on 08 Mar 2008 #permalink

Interesting! I know somebody who needs to stock up many types of sugary cookies and similar to perform a task such a writing, but also driving (which requires focused attention).

On the other hand, I tended to eat before writing, an extenuating task for sure (!), but the fact that I ate chocolate bars did no good in terms of my productivity or increased/improved my concentration span as I did not progress or finished the task of writing in way that would find myself satisfied or accomplished. However, the fact that I was eating more chocolate bars and madeleines than ever before during these years of study just served to lower my self-esteem and the only result I got is that I put on weight significantly. I associate my eating habits to two factors: 1) high levels of anxiety and stress; 2)the continuous cold and gray weather of UK that depressed me since I am originally from a tropical country where the heat put us off from eating, especially chocolates that I only ate in Europe to send away the cold sensation and feel myself "warmer" somehow.

While the person I cited in the beginning was from a Northern part of Europe. Does it matter where we are from and what kind of food habits or life styles we are used to?

I have a tendency both towards low blood sugar and troubles concentrating (I think I have ADD, never diagnosed). This is interesting AND helpful. I think it would be a good idea for me to snack before job interviews and tests, for instance.

By Samantha Vimes (not verified) on 09 Mar 2008 #permalink

This explains why dieting is so difficult: dieters are attempting to exercise self-control (at the table) at exactly the time when their blood sugar's at a minimum. So a dieter would be well advised to drink a nice glass of sugar-sweetened lemonade (or drink a glass of orange juice or the like) a quarter of an hour before sitting down to eat.

Interesting work. I know a number of teachers in my department that give the students mints at the start of an exam to help them focus.

By Marcel Grdinic, M.A. (not verified) on 12 Mar 2008 #permalink

@Leisureguy: Dieters, especially those struggling with diabetes, would be even better advised to eat some fruit before beginning their meal. Not only does it provide glucose for self-control, but it helps trigger their satiety response so that they are likely to eat less.

I'd suggest that for sustained effectiveness, snacks with a low glycaemic load ( would be better than sugary ones, particularly for people who, like me, have issues with blood sugar regulation (I have too strong an insulin response, but the commoner problem is having one that's too weak). Boosting your blood sugar too rapidly is likely to lead to a boom-bust cycle and impair your overall performance.

Yet another reason to eat more chocolate! =]

Obviously none of you have worked in a classroom after snack time. When students are bouncing off the walls entering the room and unable to sit normally due to abundant glucose levels, education does not happen. The single peppermint can be helpful with a class that has not had a recent meal, but sugar-free is still very necessary in our obese ADD climate of modern education.

By Mr. Pannell (not verified) on 02 Jan 2009 #permalink