We all know that stress can negatively impact our health in a number of different ways. It can affect things like immunity, digestion and sleep, and is also linked to acne, low libido and depression. Similarly, it’s no secret that over-indulging on calorie-dense food can not only lead to weight gain but the development of chronic diseases such as diabetes, CVD and hypertension. But what happens when you cross the two? Is it a recipe for disaster? A team led by Professor Herbert Herzog, Head of the Eating Disorders laboratory at the Garvan Institute of Medical Research found that a high-calorie diet when combined with stress, resulted in more weight gain than the same diet in a stress-free environment. The study, published in the journal, Cell Metabolism was conducted on mice where researchers observed their eating behaviour and the interplay of brain activity. The mice were split into two groups, one of which were classified as chronically stressed due to isolation and change of environment, and the other, placed in typical, nonstressful living conditions. “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,” explains Dr Kenny Chi Kin Ip, lead author of the study.
To understand what exactly controls this ‘stress eating’ the researchers looked at different areas of the brain in mice. While food intake is mainly controlled by a part of the brain called the hypothalamus, another part of the brain – the amygdala – processes emotional responses, including stress and anxiety. The researchers also highlighted a molecule called NPY to be at the centre of this weight gain. The brain produces NPY naturally in response to stress to stimulate eating in humans as well as mice. “We discovered that when we switched off the 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 the stress-free environment,” says Dr Ip. “This shows a clear link between stress, obesity and NPY.” Researchers also found that insulin had a significant impact on the amygdala. Under normal conditions, the body produces insulin just after a meal, which helps cells absorb glucose from the blood and sends a ‘stop eating’ signal to the hypothalamus feeding centre of the brain. In the study, the scientists discovered that chronic stress alone raised the blood insulin levels only slightly, but in combination with a high-calorie diet, the insulin levels were 10 times higher than mice that were stress-free and received a normal diet. “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 Professor Herzog. “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.”