People are less likely to resist tasty, unhealthy foods when they're under stress because the promise of immediate reward trumps longer-term goals to eat well, a Swiss study published in Neuron suggests.
Using brain scans, researchers found that circuits in the brain associated with reward are amped up and those linked to self-control are dialed down in participants under stress. The more stressed people felt themselves to be, the stronger the effect.
"We find that stress increases reward signaling and thus may boost a craving for getting the instantaneously rewarding option," which ties in with earlier studies of stress and decision circuits in the brain, said lead author Silvia U. Maier at the University of Zurich.
"The more stressed you feel, the less likely you become to override your own taste preferences when we present you with a really tricky challenge, say: your favorite chocolate bar versus a portion of broccoli," Maier told Reuters Health by email.
"You could say it's almost like stress is turning up the dial on signals about taste, and turning down the signal on health goals," she said.
For the study, the researchers recruited 51 young adult men who reported making an effort to eat a healthy diet and exercise regularly, but also still enjoyed junk foods with some frequency.
First, each participant used a computer questionnaire to rate images of 180 food items for healthiness, tastiness and their overall appeal.
Then 29 of the men were randomly selected to undergo the stress induction procedure, in which they immersed a hand in an ice bath for three minutes while they were videotaped and monitored. Social evaluation is one of the most potent human stressors, Maier noted.
All the participants were put in a functional magnetic resonance imaging (fMRI) scanner, which measures brain activity by mapping blood flow changes in the brain, and asked to complete several seven-minute computer-based decision trials, selecting from pairs of the foods they had previously rated on healthiness and taste.
In addition to the fMRI measures, the researchers also collected saliva samples from the men to measure the stress hormone cortisol.
As reported in Neuron, the researchers found that men who had undergone the stressful situation were more likely to favor taste rather than health in their food choices, compared to the men who had not been stressed.
"What's exciting about this work is that it identifies specific mechanisms for how stress affects self control: by amplifying the influence of short-term rewards on choices, and by impairing the influence of a brain region known to be important for self-control," said Molly Crockett, an expert in neuropsychology at University College London in the U.K.
"When you're faced with an unhealthy food that's not very tempting, stress won't affect your self control much," Crockett, who was not part of the new research, told Reuters Health by email. "But when you're faced with your most favorite tempting foods, stress will make it more difficult to resist those temptations."
In studies of rats, a high-fat diet appears to blunt the stress response, and some researchers speculate that humans may change their diets to "self-medicate" the stress response in the brain, although that is still a hypothesis, Maier said.
"One very stressful day will most likely not sabotage your diet completely if the stress ends after this day and you return back to your routine of eating a healthy, balanced diet," she said. "However, we find that even moderately stressful events may promote these lapses of self-control, and moderate stress may occur more often during your day or week."
One way to combat this effect is to use pre-commitment, removing temptations before they occur, for example removing snacks, cigarettes or alcohol from the home if you know you will have trouble resisting later, Maier said.