A striking new study from Australian researchers has discovered that eating while stressed may lead to greater weight gain than if the same caloric load was consumed in a stress-free environment. The study reveals a molecular pathway activated by stress can alter the body's metabolic processes and lead to increased weight gain.

The research began by investigating the relationship between stress and eating patterns in mouse models. Prior animal studies have revealed that while high stress scenarios generally lead to decreased food intake, when there is access to foods high in fat or sugar, stress can actually increase an animal's food intake. In humans this gels with the anecdotal idea of "stress eating," where one binges on high-calorie junk food when in stressful situations. The first, and most compelling discovery from this new research was that stress seems to strongly correlate with weight gain.

"Our study showed that when stressed over an extended period and high calorie food was available, mice became obese more quickly than those that consumed the same high fat food in a stress-free environment," says Kenny Chi Kin Ip, lead author on the new study.

Homing in on what could be specifically causing this oddly anomalous response, the researchers discovered that in high-stress situations a neuropeptide dubbed NPY is over-activated in the amygdala. It was found that it is this specific brain region that seemed to be modulating the body's response to stress and food.

"We discovered that when we switched off the production of NPY in the amygdala weight gain was reduced," says Ip. "Without NPY, the weight gain on a high-fat diet with stress was the same as weight gain in the stress-free environment. This shows a clear link between stress, obesity and NPY."

Furthermore, the research revealed that stress seemed to significantly amplify blood insulin levels, and it was these excessive insulin levels that ultimately boosted NPY activity in the amygdala. NPY activity then subsequently both increased an animal's appetite and reduced the body's ability to burn energy, thus storing a greater caloric intake as fat.

"Our findings revealed a vicious cycle, where chronic, high insulin levels driven by stress and a high-calorie diet promoted more and more eating," explains Herbert Herzog, lead on the research at the Garvan Institute of Medical Research. "This really reinforced the idea that while it's bad to eat junk food, eating high-calorie foods under stress is a double whammy that drives obesity."

The new study is fascinating from a number of perspectives. Not only does it highlight how acute stress can fundamentally alter how an animal metabolically processes a single caloric load, but it also reveals a previously undiscovered action of insulin on the brain.

"We were surprised that insulin had such a significant impact on the amygdala," says Herzog. "It's becoming more and more clear that insulin doesn't only impact peripheral regions of the body, but that it regulates functions in the brain. We're hoping to explore these effects further in future."

The new study was published in the journal Cell Metabolism.