Fat Chance

However, either chronic stress or heightened responses to stress due to ineffective coping strategies will unleash a long-term cortisol cascade. In these prolonged stressful situations, the cortisol is unregulated. Why doesn’t the cortisol feed back in the state of chronic stress to control its own release? This is one of the biggest questions in science today. Apparently, the amygdala’s ability to perceive the cortisol signal becomes reduced in response to the excess cortisol supply. Chronic exposure suppresses the negative feedback of cortisol on the brain. How and why this happens is still unknown. Whatever the mechanism, it’s a vicious cycle: stress breeds more cortisol, which in turn breeds more stress.[71 - M. F. Dallman et al., “Chronic Stress and Comfort Foods: Self-Medication and Abdominal Obesity,” Brain Behav. Immun. 19 (2005): 275–80.]

“Stressed” Is “Desserts” Spelled Backward

Over several years, prolonged cortisol leads to excessive food intake – but not just any food. Human research shows that cortisol specifically increases caloric intake of “comfort foods” (those with high energy density or high fat and high sugar). Your spouse is late and the kids won’t stop whining? Break out the Ben & Jerry’s.

What predisposes certain people to stress-induced eating? For one thing, it’s not the stress itself; it’s the response to stress. Stress, like art, is in the eye of the beholder. The same level of stress can have varying effects on different people. The perception of chronic stress causes increased caloric intake of “comfort foods,” but only among those with high cortisol reactivity. People who are “stress eaters” exhibit significant increases in insulin, weight, and cortisol at night (normally the time for cortisol to be very low) during a stressful period. My colleague Elissa Epel at the University of California, San Francisco showed that those subjects who generated the greatest amount of cortisol in response to a psychological stressor also consumed the greatest amount of high-fat, sugary food.[72 - A. J. Tomiyama et al., “Comfort Food Is Comforting to Those Most Stressed: Evidence of the Chronic Stress Response Network in High Stress Women,” Psychoneuroendocrinology 36 (2011): 1513–19.] Stress has also been postulated to play a role in metabolic syndrome in childhood, a time when eating patterns and fat cells are “programmed.”

Stress may affect food intake in several ways. One outcome of stress is reduced sleep, which is both a contributor to and a consequence of obesity. We’re all getting less sleep than we used to, especially children (Janie included).[73 - A. Sadeh et al., “Sleep Patterns and Sleep Disruptions in School-Age Children,” Dev. Psychol. 36 (2000): 291–301.] BMI increases over time among short sleepers. And just because you sleep less does not mean you are filling your waking hours with exercise. At the biochemical level, acute sleep loss is associated with elevations in markers of systemic inflammation and signs of metabolic syndrome. Sleep deprivation has been shown to increase cortisol and reduce leptin, and in doing so, mimic starvation and hunger. At the brain level, sleep deprivation increases the hunger hormone ghrelin, which increases the “value” each of us puts on food, and also activates the reward system,[74 - C. Benedict et al., “Acute Sleep Deprivation Enhances the Brain’s Response to Hedonic Food Stimuli: An fMRI Study,” J. Clin. Endocr. Metab. 97 (2012): E443–47.] making you eat even more chocolate cake. Conversely, poor sleep is common among obese individuals. This is in part because high BMI is a strong predictor of obstructive sleep apnea, which, due to retention of carbon dioxide, appears to make obesity even worse.

The role of stress and cortisol in eating extends from the physiologic to the pathologic, and from overeating to undereating. When I was a pediatric resident working thirty-six hours out of every forty-eight, our group was divided into two cohorts: those who hit the cafeteria and those who lived on coffee. I tried the coffee, but my hands shook too much when I was threading catheters into umbilical arteries on premature infants, so I turned to food. I gained 45 pounds during residency, and I haven’t taken them off yet.

A monkey model that drives cortisol up is called the variable foraging demand model, which is the animal equivalent to “food insecurity.”[75 - D. Kaufman et al., “Early-Life Stress and the Development of Obesity and Insulin Resistance in Juvenile Bonnet Macaques,” Diabetes 56 (2007): 1382–86.] In this model, monkeys have access to food in one of three ways: (1) ad lib, in which the food is available all the time; (2) at every meal, the animal has to work to find food that has been hidden in a maze of tubes; or (3) a random combination of the two, called variable foraging. Despite the fact that the animals in the second group have to work at finding their food, their body weights and cortisol levels are similar to those of the ad lib monkeys: they know what they have to do to attain their next meal. However, for the third group, the variable foragers, the uncertainty of the food availability drives up their cortisol levels and they become markedly obese.

Stress and cortisol also promote faster addiction to various drugs of abuse and likely food as well. Experiments in animals emphasize that stress or cortisol administration (particularly uncontrollable stress) increases the likelihood of abusing drugs such as cocaine. Another way to drive up cortisol in monkeys is by placing them in group housing, thereby exposing them to social hierarchy. Invariably, one animal will rise in the social order to become the alpha male, or the leader of the cage. This animal, akin to an all-powerful CEO, will have the lowest cortisol levels. The cortisol levels of the subordinates will be much higher. When all the monkeys are then provided access to cocaine for self-administration, while the alpha male won’t get hooked, the subordinates become addicts. This can also happen with food. Thus the stress and reward systems are linked, making food addiction among those who eat to manage their stress a faît accompli