It's been another hectic day. On impulse, you grab an extra-large candy bar during your afternoon break. You plan to take just a few bites. But before you know it, you've polished off the whole thing — and, at least temporarily, you may feel better.
Rest assured you're not alone. Stress, the hormones it unleashes, and the effects of high-fat, sugary "comfort foods" push people toward overeating.
Effects on appetite
In the short term, stress can shut down appetite. A structure in the brain called the hypothalamus releases corticotropin-releasing hormone, which suppresses appetite. The brain also 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 eating on hold.
But if stress persists — or is perceived as persisting — it's a different story. The adrenal glands release another hormone called cortisol, and cortisol increases appetite and may also ramp up motivation in general, including the motivation to eat. Once a stressful episode is over, cortisol levels should fall, but if the stress doesn't go away — or if a person's stress response gets stuck in the "on" position — cortisol may stay elevated.
Fat and sugar cravings
Stress also seems to affect food preferences. Numerous studies — granted, many of them in animals — 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.
Of course, overeating isn't the only stress-related behavior that can add pounds. Stressed people lose sleep, exercise less, and drink more alcohol, all of which can contribute to becoming overweight.
Some research suggests a gender difference in stress-coping behavior, with women being more likely to turn to food and men to alcohol or smoking. A Finnish study that included over 5,000 men and women showed that obesity was associated with stress-related eating in women but not in men. Other research has shown that high stress levels lead to weight gain in both women and men, but the effect is typically greater in men.
Harvard researchers have reported that stress from work and other sorts of problems correlates with weight gain, but only in those who were overweight at the beginning of the study period. One explanation: overweight people have elevated insulin levels, and stress-related weight gain is more likely to occur in the presence of high insulin.
How much cortisol people produce in response to stress may also factor into the stress–weight gain equation. Several years ago, British researchers designed an ingenious study that showed that people who responded to stress with high cortisol levels in an experimental setting were more likely to snack in response to daily hassles in their regular lives than low-cortisol responders.
Steps you can take
Stress reduction is a growth industry these days. There are dozens of things to try. Here are three suggestions:
- Meditate. Countless studies show that meditation reduces stress, although much of the research has focused on high blood pressure and heart disease. Meditation may also help you be more mindful of food choices. With practice, a person may be able to pay better attention to the impulse to grab a fat- and sugar-loaded comfort food and inhibit the impulse.
- Exercise more. Intense exercise increases cortisol levels temporarily, but low-intensity exercise seems to reduce them. University of California researchers reported results in 2010 that exercise — and this was vigorous exercise — may blunt some of the negative effects of stress. Some activities, such as yoga and tai chi, have elements of both exercise and meditation.
- Visit with friends. Social support seems to have a buffering effect on the stress people experience. For example, researchers have found that the mental health of people working in stressful situations, like hospital emergency departments, is better if they have social supports. But even those of us who live and work in situations where the stakes aren't as high will, as Lennon and McCartney suggested, be better off if we get a little help from our friends.
Get your copy of Healthy Eating: A guide to the new nutrition
Eat real food. That's the essence of today's nutrition message. Our knowledge of nutrition has come full circle, back to eating food that is as close as possible to the way nature made it. Based on a solid foundation of current nutrition science, Harvard's Special Health Report Healthy Eating: A guide to the new nutrition describes how to eat for optimum health.
Have I given up steak for nothing?
Q. I read that Harvard researchers found no association between eating red meat and developing heart disease and diabetes. Have I been depriving myself of steak for more than 20 years for no good reason?
A. In 2011 some of my colleagues at the Harvard School of Public Health reported findings from a meta-analysis that summarized the results of 20 studies. You're right: they didn't find an association between consumption of unprocessed red meat and heart disease and diabetes.
On the other hand, one serving per day of processed meat was associated with a higher risk of developing those diseases. In this and other studies, red meat is defined as beef (including hamburger), lamb, pork, and game, and processed meat as any meat preserved by smoking, curing, salting, or chemicals, which would include bacon, hot dogs, sausage, and cold cuts. The processed meat was primarily processed red meat, but in some of the studies in the meta-analysis, poultry cold cuts were also included in the processed meat category.
There were important — and unavoidable — limitations to my colleagues' meta-analysis. Only a handful of small studies broke out unprocessed red meat separately, so the conclusions were based on just a minor fraction of the data.
Furthermore, most of the studies compared calories from red meat to calories from the rest of the diet, which tended to be heavy on refined starch, sugar, potatoes, and, until recently, hydrogenated vegetable oils that contain trans fat. So red meat's lack of association with heart disease and diabetes may only mean that it's just as bad for you as those other unhealthful foods.
Our group in the nutrition department reported findings in 2010 that compared red meat with other protein sources, and it was clear that replacing red meat with chicken, fish, and nuts is associated with a lower risk of heart disease. So I don't think that curbing your appetite for steak was for naught. You improved your chances of not having a heart attack if you replaced it with these healthier options.
— Walter C. Willett, M.D.
Department of Nutrition
Harvard School of Public Health