Do you curl up with a tub of ice cream or snack on candy when you're stressed? While this habit might be comforting, it sends the wrong message to your brain and results in weight gain, reveals a new Australian study published in the Cell Metabolism review.
While we've long known that junk food is bad for our health and that stress makes us put on weight, new research highlights a brain function that is responsible for this phenomenon.
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Supervised by Professor Herbert Herzog, head of the eating disorders laboratory at the Garvan Institute of Medical Research in Sydney, Australia, the study shows that a high-calorie diet causes more weight gain when combined with stress, due to a molecular pathway in the brain.
The scientists studied two areas of the brain in mice: the hypothalamus, known for regulating eating habits, and the amygdala, the part of the brain that controls emotion, including anxiety.
"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," said Dr Kenny Ip, lead author of the study.
The cause of this weight gain was discovered to be a molecule known as neuropeptide Y (NPY), naturally produced by the amygdala in stressful situations.
"When we switched off production of NPY in the amygdala, weight gain was reduced. Without NPY, the weight gain on a high-fat diet with stress was the same as weight gain in a stress-free environment. This shows a clear link between stress, obesity and NPY," explained Ip.
To understand what stimulates the action of NPY under the effects of stress, scientists analyzed the nerve cells that produce NPY in the amygdala, and found that they were receptors for insulin, a hormone produced by the pancreas which enables sugars to penetrate the body's cells just after a meal, and sends a signal to the brain to tell it to stop eating.
The experiments on mice showed that chronic stress combined with a high-fat diet increased insulin levels in the amygdala and desensitized nerve cells to insulin. In turn, the desensitized nerve cells increased their levels of NPY.
"Our findings revealed a vicious cycle, where chronic, high insulin levels driven by stress and a high-calorie diet promoted more and more eating," said 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."
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