A University professor is getting to the bottom of why students can’t resist skipping class or cheating on their diets.

In the latest issue of Current Directions in Psychological Science, Dr. Kathleen Vohs detailed her model of self-control, which describes why it can be so hard to say no. The University marketing and McKnight Land-Grant professor points to evidence suggesting the ability to resist temptations draws on a limited pool of resource, which has now been identified as glucose.

Just like a muscle tires after exerting itself, self-control becomes more difficult after resisting temptations.

Vohs applies her research on self-control to marketing at the University. She said her research describes why and how consumers make decisions by thinking through their goals, motivations and decisions. She said she incorporates that knowledge into her consumer behavior class at Carlson School of Management.

Vohs has found evidence to support this model and the idea of depleted resources since 1994. Now, new research has identified one of those resources that Vohs is using in her model.

A new study has discovered that blood-glucose levels drop after practicing self-control.

Brandon Schmeichel, a professor at Texas A&M University, was part of the study that brought the relationship between glucose and self-control to light.

The experiment consisted of multiple rounds of self-control tests while monitoring glucose levels. After resisting a temptation – such as eating a plate of cookies or attempting not to laugh while watching a comedy – subjects showed a drop in their glucose levels and were not able to resist temptations during subsequent rounds.

Subjects who were given lemonade with sugar to drink after resisting the first temptation test showed restored glucose levels and performed at levels similar to their original tests.

Schmeichel said ingesting sugar to maintain glucose levels won’t improve self-control, but will prevent people from becoming worse at it.

“You might say that glucose prevented a negative effect on self-control, rather than increasing or having a positive effect,” he said.

Glucose plays a major role in self-control, but other factors can affect the ability despite glucose levels.

Vohs said improving mood, laughing and recalling memories that include important values can help people have self-control.

Alcohol can play an important part in lowering the ability, too.

Schmeichel said there is evidence suggesting alcohol lowers the ability to demonstrate self-control and also lowers glucose levels in the brain and body.

Vohs said when it comes down to making a decision, the strength of each temptation and the rationalizations made for each decide which will win.

In her article, Vohs said when people have depleted levels of the energy needed for self-control, their ability to override impulses, behave morally and act on rational choices all declined.

Cary Seryakov, a sociology junior, said he doesn’t worry about a depleted ability to control himself. He said he doesn’t think he is any better than others, but said he thinks sticking to decisions he makes after logically thinking them out is most important.

“Once you make a decision you should go with it,” he said. “Don’t doubt the decision.”

Phil Oommen, an independent study junior, said he lets his morals and upbringing guide his decisions when he has to resist temptations. He said his Christian faith and prayer helps him through each day.

“Every time I get tempted I pray,” he said.

Oommen said when a subject is not important or is not of major consequence to him, it is more difficult to resist temptations.

“Everyone has their downfalls,” he said.