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updated 8/6/2015 7:45:47 PM ET 2015-08-06T23:45:47

In that tough decision about whether to snack on an apple or a donut, stress may be a deciding factor, according to a new study.

The study found that a moderate amount of stress can weaken a person's willpower to choose healthier food when making food decisions.

Researchers in Switzerland asked people to choose a food to eat, after the individuals had experienced moderate stress. Results showed that the participants were more likely to pick a food that tasted good, and less likely to select a healthy food that wasn't as tasty, than if they were not stressed.

The small study also showed that the neural pathways in the brain that influence a person's desire for immediate gratification show increased activity following moderate stress, whereas the brain areas that help control willpower and that affect the desire to maintain a long-term goal, such as healthy eating, show reduced activity. The results shed light on why the brain finds it hard to resist temptation even in people with good-health intentions. [ Dieters, Beware: 9 Myths That Can Make You Fat ]

"The findings show that self-control is mediated by a complex and distributed network in the brain," said Silvia Maier, a co-author of the study and a doctoral candidate in neuroeconomics at the University of Zurich. Disturbances in any number of brain regions within this complex network can weaken self-control, Maier said.

But the new findings also suggest that there are multiple ways of enhancing self-control or preventing self-control problems, and those methods could represent exciting future avenues for research, she noted.

In the study, published today (Aug. 5) in the journal Neuron, Maier and her colleague Todd Hare, also from the University of Zurich, recruited 51 young men who were making an effort to eat healthy food and exercise regularly. (No women were involved in the study, because the stress hormone cortisol interacts with estrogen, making it harder for researchers to control cortisol levels as a variable, Maier said.)

About half of the men were asked to place their hands in an ice-water bath for 3 minutes, a situation meant to create moderate stress.

Afterward, all the men were shown photographs of two foods on a computer screen, where one food was a tastier choice and the other was a healthier item, and the participants had to select the food they wanted to eat.

The men who experienced the stress were more likely to pick unhealthy foods that tasted good, compared with the men who were not stressed.

When the researchers looked at the men's brain scans, they found that connections in the brain involved in promoting a health goal were weaker in the men who were stressed, Maier said. She explained that it's as if stress turns up the dial on the brain signals that affect taste preferences, and turns down the brain signals that promote good health.

Stress and self-control

One very stressful day will most likely not sabotage a person's diet completely, if the stress ends that day and an individual returns back to eating a healthy, balanced diet, Maier said.

But the study showed that even moderately stressful events, which tend to occur more often than chronic stress, may promote lapses of self-control, she said. As a result, if a person tends to rely on his or her willpower to exert self-control and help restrict food choices, it will be harder to eat healthy food when that person feels moderately stressed, Maier said.

The findings also revealed that there is a lot of variation in the way stress affects people, Maier said. So, a next step in this research may be to investigate why some individuals are more resilient to the effects of stress than are others. 

Maier recommended that people who are trying to eat healthy recognize that stress can make them more vulnerable to give in to food cravings. Recognizing that their brains will likely lose the struggle for self-control when temptation is highest, people may want to come up with alternative strategies that take willpower out of the equation, she suggested.

One approach may be to remove temptations before they occur, Maier said. For example, people who know they have a hard time resisting a particular snack, such as a bag of potato chips or quart of ice cream, should keep those foods out of the house, so that if a craving for that food arises, it won't be readily available to eat. 

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