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David Lewis Ph.D.


Why an Empty Bladder Could Mean an Empty Wallet

How self-control can be depleted by exercising self-control

Excuse me if I ask you a really personal question.

How full is your bladder?

Do you find yourself, perhaps because I just raised the issue, in need of a visit to the restroom?

If so then I suggest you immediately go shopping, update your stock portfolio or, indeed, take any other important decision. The chances are you’ll be less likely to act impulsively with a full-bladder than an empty one.

I’ll explain the link in a moment. But first, let’s take a look at the concept of self-control, which we typically describe as willpower.

“Self-control, is one of the defining features of the human animal,” say Michael Inzlicht of the University of Toronto and Brandon Schmeichel of Texas A&M University. “(it refers) to the mental capacity individuals have to override or alter their own thoughts, emotions, and behaviors. It relies on controlled processes to regulate urges, to juggle competing goals, and to sustain attention. Its failure is one of the central problems of human society, being implicated in phenomena ranging from criminality to obesity, from personal debt to drug abuse.” (1)

Every day, for example, people resist impulses to go back to sleep, to eat fattening or forbidden foods, to say or do hurtful things to their relationship partners, to play rather than go to work, to engage in inappropriate sexual or violent acts, and to perform a host of other behaviours that, while easy and/or enjoyable carry long-term costs or violate the rules and guidelines of acceptable behavior.

Measuring Self-Control in Marshmallows

According to some psychologists the litmus test of how much self-control a child has can be determined by how long he or she is able to resist eating a marshmallow! This was the basis of a classic study conducted at Stanford in the early 1970s by Walter Mischel. (2) In one version of his experiment, four-year-olds were left in a room with a bell, with which they could summon an experimenter who, they were promised, would give them a single marshmallow.

They were also told that if they could hold out and wait for the experimenter to return of his own accord they would receive two marshmallows.

Some children managed to wait up to 20 minutes to gain two marshmallows but most gave in to their desire for immediate gratification. The principle underlying the challenge faced by those four-year-olds is sometimes called temporal discounting.

To a small child, a single marshmallow eaten right away may appear more valuable than two marshmallows in some indefinite future.

Transposed to adult behavior, it is easy to see how temporal discounting leads otherwise rational people to compromise their long-term health and happiness for short-term gains. That giant-screen TV on sale might seem more tangibly rewarding as you stand gazing at it than some vaguely imagined future free of debt. Or tonight’s dessert special—Black Forest Gateau—may seem more important (as you observe another lucky diner enjoying it) than a slimmer waistline further down the road.

Self-Control Enhances Wellbeing

A single marshmallow, like a single impulsive action, may seem trivial. But, over the course of a lifetime, an ability to exercise self-control can make the difference between success and failure. Research has shown that people high in self-control are healthier, enjoy better relationships and are more successful in school and work than those low in willpower.

The children in Mischel’s marshmallow study, for example, were tracked through adolescence. Researchers found that the four-year-olds who successfully delayed gratification were better adjusted in later life and did better in their exams than those who had succumbed to temptation.

Exercising Self-Control Weakens Self-Control

One of the main limits on our self-control turns out, paradoxically, to be self-control itself! A number of studies have shown that executive processes by which we control our impulses behave a lot like muscles that get tired through use. Exerting self-control in one area of life—a condition which psychologist Roy Baumeister termed "ego-depletion"—makes it harder to exert self-control in another, at least right away.

In one study, a group of hungry participants was forbidden from eating freshly baked cakes placed on a plate in front of them and made to eat radishes instead! (3)

These participants gave up faster on a frustrating task than did a control group who had been allowed to indulge their sweet tooth. In another, participants were instructed to suppress all thoughts of a white bear for five minutes. Immediately afterwards, they drank more beer in a supposed “taste test”—despite knowing they would subsequently be taking a driving test—than did members of the control group. (4)

Which could mean that refraining from having a fight with one’s boss during the day may make it harder for you to resist binging on comfort food that evening. The constant effort of sticking to a diet may cause us to make more impulsive purchases at the mall.

The brain regions that control willpower do much more than simply keep our impulses in check. They form part of a larger set of executive functions involved in self-monitoring, coping with stressors, weighing alternatives, and making decisions, all of which draw on the same limited energy source. (5)

In one study, students required to choose between a variety of courses subsequently studied less hard for a math test, opting to play video games or read magazines instead.

Watching is as Depleting as Doing

It is even possible to become ego-depleted merely by watching others exerting willpower. In a recent study by Kathleen Vohs and her colleagues, participants were asked to put themselves in the shoes of a fictional hungry waiter or waitress in a gourmet restaurant who is forbidden from eating on the job. They then viewed pictures of various products like watches, cars, and appliances and rated how much they would be willing to spend for them.

Having to exercise vicarious self-control led people to be willing to spend more on the consumer goods, as compared with a control group. (6)

The Full Bladder Study

Which brings us back to having an uncomfortably full bladder!

In the experiment, participants either drank five cups of water or took small sips of water from five separate cups. After some forty minutes—the amount of time it takes for water to reach the bladder—researchers assessed participants’ self-control by asking them to make a number of choices.

These offered either a small, but immediate, reward or a larger, but delayed, reward. For example, they could choose to receive either $16 the following day or $30 in 35 days time. Researchers found people with full bladders were better at holding out for the larger reward later. Other experiments reinforced this link; for example, in one, just thinking about words related to urination triggered the same effect! (7)

So maybe you should drink a bottle of water before making a decision about having a second helping of that delicious cream éclair or impulsively pressing the ‘buy’ button on your favourite web-site. Or maybe stores should make a restroom available to customers. With an empty bladder they might be more willing to splash out impulse buys.

“We are our choices”, said the French philosopher Jean Paul Sartre and it is certainly true that it is our decisions—often made impulsively and unconsciously—that can shape our future.


(1) Inzlicht, M & Schmeichel, B.J. (2012) What Is Ego Depletion? Toward a Mechanistic Revision of the Resource Model of Self-Control Perspectives on Psychological Science 7 (5) 450–463

(2) Mischel, H. N. & Mischel, W. (1983). The development of children’s

knowledge of self-control strategies. Child Development 54: 603–19

(3) Baumeister, R. F., Bratslavsky, E., Muracen, M. & Tice, D. M. (1998). ‘Ego depletion: Is the active self a limited resource?’ Journal of Personality and Social Psychology 74: 1252–6

(4) Muraven, M., Lorraine, C. R. & Neinhaus, K. (2002). ‘Self-control and alcohol restraint: An initial application of the self-control strength model’. Psychology of Addictive Behaviours 16 (2) 113–120

(5) Vohs, K.D., Baumeister, R.F., Nelson, N.M., Rawn, C.D., Twenge, J.M.,

Schmeichel, B.J., & Tice, D.M. (2008). Making choices impairs subsequent self-control: A limited resource account of decision-making, self-regulation, and active initiative. Journal of Personality and Social Psychology, 94 (5) 883-898

(6) Vohs, K. D. & Faber, R. J. (2007). Spent resources: Self-regulatory resource availability affects impulse buying. Journal of Consumer Research 33: 537–47.

(7) Tuk, M.A., Trampe, D. & Warlop, L. (2011) Inhibitory Spillover: Increased Urination Urgency Facilitates Impulse Control in Unrelated Domains Psychological Science, 22(5) 627-633