A stressfulmoment. Your brain sends messages to the adrenal glands atop the kidneys to pump out the hormone epinephrine (also known as adrenaline). Epinephrine helps trigger the body's fight-or-flight response, a revved-up physiological state that temporarily puts your rest-and-digest system on hold. A structure in your brain called the hypothalamus suppresses appetite (via corticotropin-releasing hormone). Your brain and body are in survival mode at this moment, so nutrition and digestion are not of primary importance. Your favorite dessert is likely the last thing on your mind if you, for instance, come face to face with a wild bear.
Another stressful moment... and another. Another stressful day... and another.
Stress persists — or is perceived as persisting — and your brain and body tell a different story. The adrenal glands release another hormone called cortisol -- commonly known as stress hormone. Under stressful conditions, cortisol provides your body with glucose (for science-minded: by tapping into protein stores via gluconeogenesis in the liver). This energy can help you fight or flee a stressor in the short run - that wild bear I mentioned earlier. However, elevated cortisol over the long term consistently produces glucose, leading to increased blood sugar levels.
And here is where it gets even more interesting or should I say concerning for our health! Consistently high blood glucose levels (along with insulin suppression - it's a complicated process you see) lead to cells that are starved of glucose. Yet, those cells are crying out for energy, and one way to regulate is to send hunger signals to the brain. This can lead to overeating. Researchers at the University of California-Davis recently found that 80 percent of people in their study reported eating more sweets when they are stressed.
Yep, you can blame that cortisol for increases in appetite. Stress affects food preferences. Numerous studies have shown that physical or emotional distress increases the intake of food high in fat, sugar, or both. High cortisol levels, in combination with high insulin levels, may be responsible. Other research suggests that ghrelin, a "hunger hormone," may have a role. Once ingested, fat- and sugar-filled foods seem to have a feedback effect that inhibits activity in the parts of the brain that produce and process stress and related emotions. So part of our stress-induced craving for those foods may be that they counteract stress through a complex metabolic pathway.
Of course, we shouldn't conclude that sugar should be used as a stress reliever as there are so many negative consequences of sugar consumption. For instance, unused glucose is eventually stored as body fat. So stress + dessert = weight gain.
Once a stressful episode is over, cortisol levels should fall, but if the stress doesn't go away — or if your stress response gets stuck in the "on" position — cortisol may stay elevated. This means more desserts! Moreover, overeating isn't the only stress-related behavior that can add pounds. Stressed people exercise and sleep less and drink more alcohol -- all of which can contribute to those desserts becoming a permanent fixture in your body.
Adapted from Hellhammer DH, Wust S, Kudielka BM. Salivary cortisol as a biomarker in stress research. Psychoneuroendocrinology. 2009;34,(2):163-171; Epel E, Lapidus R, McEwen B, Brownell K. Stress may add bite to appetite in women: A laboratory study of stress-induced cortisol and eating behavior. Psychoneuroendocrinology. 2001;26(1):37-49; http://www.health.harvard.edu/healthbeat/how-stress-can-make-us-overeat; http://well.blogs.nytimes.com/2015/04/23/sugar-as-a-stress-reliever/; http://www.npr.org/sections/thesalt/2016/09/27/494922257/chill-out-stress-can-override-benefits-of-healthy-eating
Doggone it, why aren't these affirmations working?