PHYSICAL SIDE OF EATING AND HUNGER: BRAIN CHEMICALS AND MOODS
Brain chemicals do more than regulate behavior. They also determine our moods. An imbalancetoo much or too little of a given substance-can produce symptoms of mental disorder ranging from depression to the abnormal elation and hyperactivity known as mania.
As we have seen, the incidence of depression in relatives of eating-disordered people is higher than the rate found in the general population. Researchers have long been intrigued by this apparent connection between eating disorders and affective disorders (mood disorders, such as depression and mania). Is it possible that both types of illnesses arise from a common source?
We don’t yet have all the evidence we need to answer this question with confidence. However, there is no doubt that disruption along certain neurochemical pathways can lead to disturbed moods of varying severity.
Consider, for example, some of the fairly common syndromes in which feelings of depression play a part. The first, and most widely known, is PMS-the premenstrual syndrome. Symptoms of PMS include sudden mood swings, irritability, anxiety, feelings of hopelessness, difficulty concentrating, sleep disturbance, food cravings, and physical problems such as headaches or joint pain.
Another illness that has received considerable publicity in recent years is SAD, or seasonal affective disorder. With the onset of winter and its shorter days, people with SAD begin to feel depressed, hopeless, and lethargic. The illness is particularly troubling because during the summer these same people are lively, outgoing, and energetic. The contrast can be confusing, not just to the patient, but to family, friends, and co-workers as well.
Less familiar is the syndrome known as CCO, or carbohydrate-craving obesity. The name is self-explanatory: Patients with this condition overeat carbohydrates to the point of severe, health-threatening obesity. A variant of this illness is a form of bulimia in which patients, usually mildly obese women, engage in severe bingeing, often involving carbohydrate-laden foods, but with little or no vomiting.
These conditions share certain symptoms, including depression, lethargy, difficulty concentrating, and periodic bouts of overeating leading to weight gain. People with these disorders seem specifically to prefer carbohydrates above all other foods. One of my patients, who as it turned out had SAD, described herself as a “bread and pasta fiend” in the winter, while in the summer she ate more protein.
Bouts of depression in SAD, as its name suggests, appear in a cycle determined by the changing seasons. PMS strikes regularly every month (though it is worse for some people during the winter months). CCO, however, seems to trigger abnormal eating virtually every day, most often in the late afternoon or early evening. It’s this regular rhythm-seasonal, monthly, daily-that caught the attention of investigators concerned with the ways our bodies change over the course of time.
We now know that many of our bodily functions operate on what is known as a circadian cycle. Circadian means “about a day.” The word refers to the fact that many natural functions- sleep, hunger, sexual arousal-are not discrete events but rhythmical processes that continue over a period of approximately twenty-four hours, with peaks and valleys that occur at different times. As a rule, these processes are regulated by the hypothalamus.
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