People with NES overeat in the evening and even awaken from sleep to eat one to two times a night on average, according to Kelly Allison, Ph.D. They consume one-quarter or more of their daily food intake after their evening meal, said Allison, a research assistant professor of psychology in psychiatry at the University of Pennsylvania School of Medicine and director of a NES-focused cognitive-behavioral therapy (CBT) study.
People with NES typically lack appetite in the morning. Some curb their daytime food intake, knowing they will graze after dark.
Not all people with NES are obese. Some maintain normal weight via daytime food restriction or intensive exercise. These individuals typically are younger by about a decade than obese people with NES, suggesting NES may serve as a pathway to obesity.
Many people with NES keep a small refrigerator next to the bed, favoring peanut butter, popsicles, candy bars, nuts, and sometimes fruit as handy middle-of-the-night snacks. They rely on food as an aid to returning to sleep, probably a conditioned response, Allison reported.
People with NES remember what they eat in the night, unlike people with sleep-related eating disorder (SRED), a rare parasomnia [similar to sleepwalking]. Those with SRED often have only partial recall of having consumed frequently unpalatable items, such as buttered cigarettes, raw bacon, or cat food.
"We think NES represents a dysregulation of circadian patterns of food intake, but without disruption of the circadian sleep pattern," he explained. "NES is primarily an eating disorder, and only secondarily a sleep disorder." While appetite normally shuts down in sleep, NES appears to be a rare clinical example of an uncoupling of eating and the sleep/wake cycle. Its cause has not been determined.
"While people with NES who stay on sertraline continue to do well," Allison notes, "learning CBT strategies may give them a better long term prognosis."