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Accompanying the mid-morning coffee with a doughnut, attacking the bag of chips in the aperitif or surrendering to lasagna when you get home from work can seem like small rewards immersed in a stressful workday. However, recent research indicates that they are a very bad choice, and not only from a nutritional point of view, but because they favor a vicious circle that, in the long run, modulates brain responses and from which it can be very difficult to leave.
This is the main conclusion of a study carried out by the group of Herbert Herzog, director of the Eating Disorders laboratory at the Garvan Institute of Medical Research, in Sydney (Australia).
In animal models, scientists have described how chronic stress overrides the brain's natural response to satiety, causing the pleasure to be derived from food to decrease, and instead favors an increase in signals seeking "rewards," which translates into a hedonistic race toward eating more and more appetizing foods.
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- Editor: DANILO DI DIODORO (CORRIERE DELLA SERA)
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Thus, the research, whose results have just appeared in the journal Neuron, shows that exposure to stress influences the functioning of a part of the brain, the lateral habenula, which when activated usually dampens reward signals. But when a hypercaloric diet is added, the result is a greater preference for sweet and appetizing foods, and, in the long run, weight gain and obesity.
The authors are categorical: "Chronic stress encourages the consumption of appetizing foods and can enhance the development of obesity," they write in this article whose first author is Chi Kin Ip, of the Garvan Institute.
Professor Herzog explains that normally, the brain's responses to a high-fat diet and stress are channeled through different neural pathways. On the one hand, "a long-term high-fat diet leads to an adjustment of homeostatic regulatory pathways that reduce the urge to eat and, at the same time, increase energy consumption, especially by increasing the basic metabolic rate and producing heat to counteract excess energy supply."
And, on the other hand, "stress, in an acute context, promotes increased energy consumption to immediately cope with the stressful (dangerous) situation."
The malicious alliance arises when the "dangerous" situation becomes chronic: "In a chronic context, stress modulates the hedonic system of energy homeostasis, which is powerful enough to override the normal homeostatic control mechanism that normally prevents overeating." In short, says the scientist by email, "in a chronic context, stress is the dominant partner."
This vicious cycle is orchestrated in the brain by the neuropeptide NPY, a molecule that the body produces naturally in response to stress. When the researchers blocked NPY in the lateral habenula cells of stressed mice receiving a high-fat diet, the animals consumed less food, and weight gain was slowed.
How to break that cycle
Can NPY be used to develop treatments that promote satiety? Although it is highly conserved in evolution and is identical between mice and humans, as well as the neural pathways that control it, confirms Professor Herzog, this molecule involved in food and stress, "also intervenes in the regulation of many other brain functions, such as thermoregulation and heart rhythm", which makes it difficult to use as a therapeutic target.
However, it points to a much simpler and more accessible option to break this vicious circle.
According to the study, stressed mice fed a high-fat diet consumed three times more sucralose (a sweetener) than those on only a high-fat diet. However, they did not observe that preference for sugar water in stressed mice following a normal diet.
So the researcher points out that the study "is a reminder that you have to avoid a stressful lifestyle and, especially – if you suffer from long-term stress – try to follow a healthy diet and put aside junk food."
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