Why we eat when we study – The Brain and Self-Control

Tabitha Gan underwent an internship at the Science Centre Singapore (SCS) in December 2014. She has written this blog post during her internship at SCS.

Source: foodwallpaper.info

Snack companies spend millions of dollars trying to find that perfect blend of spices, chemicals and textures to hook us in- and they’ve succeeded to some extent. We know that snacking on what we call ‘junk food’ isn’t good for our health, and most people try to eat in moderation. But during the dreaded exam period, it seems harder to control our junk-food-eating impulses. We put it down to ‘stress’, but could there be another reason?

Researchers have found that generally, a person has a limited pool of self-control which is used for a multitude of tasks- i.e. making decisions, studying, working, or controlling emotions. This is called ego depletion. When you exert self-control in one area- i.e. studying, you’d likely have less self-control in another area i.e. resisting that bag of chips, getting angry at someone or making good decisions. Hence when students study for longer hours and put in more mental effort than usual during examinations, this leads to additional mental fatigue and less self-control when being tempted with a bag of snacks.

One of these pioneering studies was headed by American psychologist Roy Baumeister in 1998. The researchers placed two bowls of items in a room- one bowl contained red and white radishes, the other, freshly-baked chocolate chip cookies and chocolates. The cookies had been baked in the room beforehand so the room would smell like chocolate-chip cookies.

Source: makeameme.org
Source: makeameme.org

As the first part of this experiment, one group of lucky participants of this study were instructed to eat a few chocolate-chip cookies or chocolates while some poor souls were instructed to eat a few radishes. A third group skipped the food section of this experiment. After fifteen minutes, the participants were all given an unsolvable problem-solving question to work on.

As seen in the results table below, the participants in the radish group gave up much earlier than the participants in the other two groups.

Condition Average time (mins) before giving up Average no. of attempts






Control (No food)



In Baumeister’s paper, he explained that the result shows that both resisting temptations (not being able to eat the chocolate) and eating the radish (an apparently less desired act) have depleted the self-control for the first group of participants. Hence when it came to the second part of the experiment (puzzle-solving), they have lesser willpower to complete the task, hence giving up earlier. These results constituted the foundation for the hypothesis of ego depletion.Since the 1998 study, a number of other studies have been done on the topic of self-control, glucose, and ego depletion. Several studies have found that the glucose level in the bloodstream is related to performance. Another 2007 study even showed that after doing a mentally draining task, consuming lemonade containing glucose helped restore depleted self-control levels and improve cognitive performance- whereas consuming lemonade sweetened with artificial sweeteners had no such beneficial effect. Yet, this was disputed by some other studies which found that gargling glucose would also be able to activate brain regions tied to reward and self-control.

Source: Knowyourmeme.com
Source: Knowyourmeme.com

Even so, whether or not glucose intake plays a part in restoring willpower, this isn’t to say that you should cram sweets and sugar into your mouth each time you open your textbook to study!

Sleep and your body’s natural rhythms also affect how you study and what you remember. For more information about what affects your brain and body, come down to the Human Body Experience and the Brain exhibitions at the Science Centre.

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