It is readily agreed that emotional disturbance affects appetite and eating, but the precise nature of this effect is variable. In nonhuman animals, arousal tends to promote feeding. Nonspecific activation may render them more responsive to external, food-related stimuli, which direct behavior toward eating (33). (Such external responsiveness is presumably not specifically directed at food-related stimuli; rather, it focuses on whatever powerful behavior-relevant stimuli may dominate the animal's immediate perceptual environment, and might yield sexual, aggressive, or other stimulus-bound behavior depending on the environmental configuration that obtains when activation occurs.) It has been suggested that any sort of activation or drive induction might accentuate stimulus-bound eating in humans (C. P. Herman et al., unpublished data). Such stimulus-bound eating would not necessarily increase intake but rather make it more responsive to environmental conditions; if the food were bad-tasting, it might suppress eating. Such a mechanism might explain why hungry organisms sometimes eat less of a bad-tasting food than non-deprived organisms do (22,23).
Studies of arousal in humans tend to focus on particular valenced emotions (eg, anxiety, depression, and anger). In general, such negative emotions have developed a reputation for suppressing eating, even when palatable food is available. This effect is usually attributed to the sympathomimetic effects of emotional distress; these effects presumably act to suppress peripheral hunger signals. Clinical depression is indexed by a loss of appetite, among other criteria. Still, some depressed individuals tend to eat more and gain weight (34). Indeed, emotional agitation tends to increase eating among many people, to the point where emotional disturbance is often cited as a prime cause of weight gain and failure to maintain dietary restraint. How can these contradictory effects be reconciled?
It does appear to be the case that strong negative emotions produce physiological effects that oppose appetite. (It seems conceivable that minor agitation or disturbances might stimulate eating in humans much as seems to be the case in other animals, but such weak manipulations have not been explored.) Powerful distress (eg, intense clinical depression) probably suppresses appetite for virtually everyone, but short of overwhelming distress, emotional agitation appears to have opposite effects depending on the type of individual involved. Normal eaters, whose behavior is at least partially governed by the sort of hunger and satiety signals discussed previously, tend to respond to distress by eating less. Individuals who ordinarily attempt to suppress their eating (ie, dieters, including perhaps most of the obese), however, tend to eat more when they are upset (and possibly when elated, although studies of the effects of positive moods are so few as to defy conclusiveness). Dieters, because they must overcome normal physiological controls on eating if they are to succeed in reducing their intake, eventually dissociate their eating from such controls in favor of cognitive calculations of appropriate intake (see "Cognitive Factors"). Their intake is deliberately inhibited, but such inhibitions are vulnerable to disruption by (among other factors) emotional agitation. The emotionally distressed dieter, then, becomes disinhi-bited and overeats, unconstrained by the sort of normal satiety considerations that depend on physiological signals and conditioning, both of which are functionally atrophied in the dieter. The effects of distress may be exacerbated or attenuated depending on the type of distress involved; for example, physical threats tend to have a stronger suppressive effect, whereas ego threats tend to have a more facilitative effect (35; C. P. Herman et al., unpublished data, 1998). The exploration of overeating under conditions of distress remains a prominent concern of researchers studying obesity and especially bulimia nervosa.
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