This is your brain (and appetite) on stress

Have you heard of the book French Women Don't Get Fat? Apparently French women stay thin by lingering over three hour lunches, eating morsels of triple cream cheese washed down by lots of red wine and witty conversation, and strolling along the Seine in stilettos. Meanwhile we Americans work longer hours and take fewer vacations than ever, grab fast food while racing from one overscheduled child's activity to the next, and gain more and more weight.

The obvious connection between our stressed out lives and our expanding national waistlines would seem to be that we have become too busy to eat healthfully or exercise enough – but there's more to it than that. Evidence is mounting that stress has a physical effect on the brain (and gut) which causes us to eat more –especially sugars and starch—and digest our food less efficiently.

Our bodies' reaction to a perceived threat, called the "stress response," is to release of adrenaline and cortisol and suppress digestion, reproductive hormones, and the "feel good" brain chemical serotonin. We have evolved this system to deal with short term stressors, like being chased by tigers back in caveman days. In modern life, unfortunately, the "tigers" never seem to retreat; they assault us round the clock in the form of traffic, overwork, violent television, and other stressors.

Often we overeat in response to the chemical changes caused by stress, especially the rise in cortisol, which stimulates appetite, and the depletion of serotonin, which increases craving for sweet and starchy foods. Another substance, neuropeptide Y (NPY) increases appetite, especially for carbohydrate-rich food, and certain types of stress increase NPY levels. In the latest research, investigators from Georgetown University showed that NPY stimulates the growth of abdominal fat cells in mice under conditions of chronic stress. When the researchers inhibited NPY and subjected the mice to two types of stress, they were able to prevent fat accumulation. The report may point to a new target for weight loss drug development.

Some researchers also think that the very act of eating irregularly and on the run—which people may do when they are stressed and lack time— may contribute to obesity. Neurological evidence indicates that the brain's biological clock — the pacemaker that controls numerous other daily rhythms in our bodies — may also help to regulate hunger and satiety signals. Ideally, these signals should keep our weight steady. They should prompt us to eat when our body fat falls below a certain level or when we need more body fat (during pregnancy, for example), and they should tell us when we feel satiated and should stop eating. Close connections between the brain's pacemaker and the appetite control center in the hypothalamus suggest that hunger and satiety are affected by temporal cues. Irregular eating patterns may disrupt the effectiveness of these cues in a way that promotes obesity. In a related observation, it has been noted that when people are on vacation, even if they are eating more calories than usual, they often do not gain weight because they are eating in a more relaxed way (like those lucky French women, presumably).

The Bottom Line

Maybe your weight problem is really a stress problem. Meditation, yoga, exercise, sleep, exposure to sunlight, and pleasurable social interaction can all counteract the effects of stress on the brain and, it would seem logical, on weight.

Do you find that you eat more when you're under stress? What do you do to combat the cravings when you're having a stressful day?

Dr. Suzanne Koven practices internal medicine with a special interest in weight issues at Massachusetts General Hospital in Boston, and teaches at Harvard Medical School.

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