Psychology
2012. Vol.3, No.11, 987-990
Published Online November 2012 in SciRes (http://www.SciRP.org/journal/psych) http://dx.doi.org/10.4236/psych.2012.311148
Improved Self-Control Associated with Using Relatively Large
Amounts of Glucose: Learning Self-Control Is Metabolically
Expensive
Matthew T. Gailliot
Psychology Department, Stephen F. Austin State University, Nac o g doches, USA
Received August 15th, 2012; revised September 14th, 2012; accepted October 12th, 2012
The current study examined whether changes in glucose during a self-control task would predict changes
in self-control performance later on. Participants attended two experimental sessions, spaced two weeks
apart. During each session, they had their glucose measured, completed the Stroop task as a measure of
self-control, and then had their glucose measured again. Larger decreases in glucose (from before to after
the Stroop task) during the first session predicted larger increases in improvement on the Stroop task dur-
ing the second session, in the form of increased speed. Learning self-controlmight benefit from using lar-
ger amounts of glucose. Learning self-control is metabolically expensive. These findings raise the possi-
bility that self-control fatigue occurs because metabolic energy is depleted during the learning of self-
control.
Keywords: Self-Control; Self-Regulation; Glucose; Metabolism; Learning; Fatigue; Energy; Memory
Introduction
Humans are metabolic organisms. Every thought, behavior,
and biological process requires the use of metabolic energy.
Some processes are metabolically expensive, however, and
consume more energy than do others (Aiello, 1997; Aiello,
Bates, & Joffe, 2001; Aiello & Wheeler, 1995; Gailliot, Hilde-
brandt, Eckel, & Baumeister, 2009). The current study tested
whether learning self-control is metabolically expensive, such
that improved learning would be associated with using larger
amounts of one metabolicenergy source—glucose.
Past work suggests that cognitive learning is metabolically
expensive. Children use a relatively large amount of glucose for
the brain, disproportionately more than adults do (Haymond,
1989), and childhood is a time of learning large amounts of
information. Several studies demonstrate that memory is im-
proved when glucose levels are optimal, such as after having a
glucose drink (for reviews, see Riby, 2004; White, 1991).
Memory is one form of learning, as the individual encodes,
stores, and retrieves information for later recall or recognition.
If glucose benefits learning among children and memory, then
glucose might benefit learning self-control.
Learning can be viewed as a form of growth, because learn-
ing occurs partly through neuronal spreading or the growth of
neurons. Growth is metabolically expensive.
Cancer cells are one form of growth, and they use a relatively
large amount of metabolicenergy, relative to non-cancerous
cells (Schoen et al., 1999; Weber et al., 2003; Younes, Lechago,
Somoano, Mosharaf, & Lechago, 1996). Other forms of bio-
logical growth, such as sperm production (Pitnick, Jones, &
Wilkinson, 2006), can also be metabolically expensive. To the
extent that learning self-control entails growth, such as among
neurons, then glucose would be expected to improve learning
self-control.
Using self-control is metabolically expensive, suggesting that
learning self-control might be also. Several studies have found
that, after using self-control in one domain (e.g., thought sup-
pression), self-control is impaired in any other domain (e.g.,
emotion regulation) (for reviews, see Baumeister, Gailliot,
DeWall, & Oaten, 2006; Baumeister, Vohs, & Tice, 2007;
Gailliot, 2009; Muraven & Baumeister, 2000). This effect ap-
pears to occur because self-control is impaired when glucose is
low, and using self-control reduces glucose in the bloodstream
(De- Wall, Baumeister, Gailliot, & Maner,2008; Fairclough &
Hous- ton, 2004; Gailliot et al., 2007; Gailliot & Baumeister,
2007; Gailliot, Peruche, Plant, & Baumeister, 2009; Masicampo
& Baumeister, 2008). Other work shows that self-control is im-
paired by other metabolic problems, such as low brainglycogen,
diabetes, glucose-6-phosphate dehydrogenase deficiency, and
glucose intolerance (DeWall, Gailliot, Deckman, & Bushman,
2009; Gailliot, 2008; Gailliot & Baumeister, 2007).
Thus, people might be better at learning self-control when
they use larger amounts of glucose while exerting self-control.
Using more glucose might indicate more effective learning or
growth.
Participants in the current study attended two experimental
sessions, spaced 2 weeks apart. During each session, partici-
pants completed the Stroop task as a measure of self-control,
before and after which their blood-glucose levels were assessed.
If glucose reductions benefit learning, then using more glucose
during the first session should predict greater improvements on
the Stroop during the second session.
Method
Participants
The final sample included 50 college undergraduates (30
women, 20 men) who participated in exchange for credit to-

M. T. GAILLIOT
ward a course requirement. The final sample excluded 11 par-
ticipants who did not return for the second experimental ses-
sion and 3 participants for whom procedural errors by an ex-
perimenter precluded analyzing their data.
Procedure
Participants attended two experimental sessions, spaced 2
weeks apart. During each session, participants first completed a
questionnaire packet unrelated to the current investigation.
They then had their blood-glucose levels measured, completed
the Stroop task, and then had their glucose levels measured
again.
Blood samples were taken with single-use blood sampling
lancets. Blood glucose levels were measured (mg/dL) using an
Accu-chek compact meter.
Participants completed the Stroop task for 20 minutes. For
the Stroop task, participants were given a list in which the
words red, blue, and green appeared in an incongruent font
color (either red, blue, or green). Participants were instructed to
statealoud the color of the ink and to ignore the meaning of the
word, and to do this as quickly and accurately as possible. The
experimenter recorded the number of errors and speed (number
of trials completed).
Results
Speed on the Stroop
The change in glucose (from the first to the second glucose
reading) during the first session predicted change in speed on
the Stroop (number of trials completed) from the first to the
second session, r(50) = –.30, p < .05. Larger decreases inglu-
cose during the first session predicted larger increases in the
number of trials completed. Thus, larger drops in glucose were
associated with greater improvements in performance.
Errors on the Stroop
The change in glucose (from the first to the second glucose
reading) during the first session did not predict change in errors
on the Stroop from the first to the second session, p > .5 8. The
relationship between glucose changes during the first session
and changes in speed across sessions did not appear attributable
to errors, such as if a speed-accuracy tradeoff existed. Specifi-
cally, glucose changes during the first session and changes in
speed remained significantly correlated when controlling for
changes in errors, r(47) = –.29, p < .05.
Glucose Changes during the Second Session
Changes in glucose (from the first to the second glucose
reading) during the second session did not predict change in
performance across the two sessions for either speed or accu-
racy, ps > .80. This is inconsistent with the alternative explana-
tion that people prone to experience glucose drops during the
Stroop task also are prone to improve their perfo rmance.
Discussion
The current study found that larger decreases in glucose
while performing the Stroop task predicted larger increases in
improvement in speed on the Stroop during a second experi-
mental session. Presumably, glucose is used during the Stroop
as participants learn how to perform the task, and larger
amounts of glucose consumption indicate greater learning.
These findings are consistent with past work on glucose and
metabolism. Glucose enables learning (e.g., among children,
during memory tasks) and growth (e.g., in cancer cells), and is
strongly linked to self-control. Glucose seems to enable effect-
tive learning of self-control, perhaps through neuronal growth
occurring while learning how to perform well on the Stroop.
The exertion of self-control in specific ways is difficult at
first but may eventually become automatized (Bargh, 1994;
Bargh & Chartrand, 1999). Initial attempts at quitting smoking,
for instance, can be effortful, but eventually people might learn
how to avoid smoking automatically. If so, then the initial de-
velopment of self-cont rol is metabolically costly but eventually
might require less metabolic energy as the capacity is auto ma-
tized.
It is plausible that people perform worse on self-control tasks
after having usedself-control (Baumeister et al., 2007; Gailliot,
2009; Muraven & Baumeister, 2000) because glucose decreases
(Fairclough & Houston, 2004; Gailliot et al., 2007) during the
initial self-control task as people learn how to perform it. Hence,
self-control impairments after initial self-control might be con-
sidered as harmful aftereffects of learning. People who learn the
self-control task most effectively might be the most likely to
show impairments on later self-control tasks. Learning self-
control could be metabolically expensive because neurons must
not only fire as usual but also expand and grow.
Studies on the aftereffects of using self-control have found
little or no evidence that general individual differences moder-
ate the effects of self-control on later self-control. Individual
differences that have emerged tend to be related to the relevant
self-control domain, such as differences in eating restraint mod-
erating eating consumption (Kahan, Polivy, & Herman, 2003;
Vohs & Heatherton, 2000), the motivation to respond without
prejudice moderating effects of stereotype suppression (Gailliot,
Plant, Butz, & Baumeister, 2007), the temptation to drink alco-
hol moderating alcohol consumption.
(Muraven, Collins, & Nienhaus, 2002), sex drive moderating
sexual restraint (Gailliot & Baumeister, 2007), and attachment
style moderating interpersonal functioning (Vohs, Baumeister,
& Ciarocco, 2005). It is possible that individual differences in
learning might moderate self-control fatigue effects across dif-
ferent self-control domains, because learning tendencies can be
domain general.
Gailliot et al. (2007) found (but did not report) that decreases
in glucose predicted impaired performance on later self-control
tasks, though glucose levels more reliably predicted self-control
performance. Whereas past work thus highlights the link be-
tween glucose levels and self-control (Fairclough & Houston,
2004; Gailliot et al., 2007), the current work suggests that
changes in glucos e levels also are influential.
People with diabetes and other metabolic problems tend to
exhibit impaired self-control (e.g., DeWall et al., 2009; Gailliot
& Baumeister, 2007). Their problems with self-control could
stem from difficulties learning to effectively exert self-control.
They might form self-control intentions and act upon them
much like individuals without metabolic deficits, yet experience
problems with learning.
Metabolic energy use is limited (Kleiber, 1961), suggesting
that metabolites used for one processes can be diverted away
from others (Gailliot et al., 2009). If so, then metabolism used
988

M. T. GAILLIOT
for learning might at times be diverted from other processes and
viceversa. Immune functioning and reproduction are metaboli-
cally expensive, and so learning might exhibit metabolic trade-
offs with health and reproductive capacity, for instance.
Demands to learning self-control could be related to metabo-
lism in ways aside from causing decreases in glucose. For ex-
ample, increased demands to learn self-control might lead to
increased metabolic energy intake, such as gaining weight in
novel environments.
Future work could focus on why learning self-control might
be a metabolically costly part of self-control. Learning might
entail greater changes in neuronal firing and connections, thus
requiring more energy than more simple neuronal activity.
Change requires growth and the additional metabolites to sup-
port that growth, which is above the typical rate of glucose use
during that same amount of time.
Failures in self-control might stem from failures in learning
how to exert self-control as much as they stem from failures in
exerting self-control. People might lack the glucose needed to
effectively learn superior self-control strategies, for instance,
such as a dieter failing to learn how to walk away from the
kitchen and engage in an activity other than eating. The indi-
vidual might experience thoughts helpful toward successful
self-control, but without sufficient glucose, fail to learn from
them.
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