Night-Eating Syndrome: A Unique Eating Disorder

The night-eating syndrome (NES) appears to be distinctly different from anorexia nervosa, bulimia nervosa, or binge eating disorder, according to results of studies in Norway and at the University of Pennsylvania (JAMA 1999; 282:657)

The night-eating syndrome is associated with morning anorexia, evening hyperphagia, and insomnia. Night eating is thought to be brought on by stress and is believed to affect about 2% of the general population (Int J Eat Disord 1997; 22:65), about 9% of obese patients, and about 27% of severely obese persons (Psychiatr Q 1959; 33:284).

Two studies look at behavior, endocrine changes

Two studies that examined the behavioral and neuroendocrine sides of this disorder have better defined this perplexing condition. The behavioral study, conducted by Dr. Albert Stunkard and his colleagues at the University of Pennsylvania, measured timing of energy intake, mood level, and sleep disturbances.

Subjects included 10 obese persons (8 women and 2 men) who met the criteria for NES and 10 matched controls who were observed in an outpatient setting. Four subjects with bulimia nervosa were added to the protocol as a comparison group. Twenty-four-hour food intake data were collected for one week.

The neuroendocrine study, conducted during a 24-hr period while subjects were inpatients at University Hospital, Tromsö, Norway, charted circadian levels of plasma melatonin, leptin, and cortisol. The study group included 12 night-eaters and 21 control subjects, all women.

Behavioral study: Half of calories between midnight and 6 am

The amount of food intake by night eaters and controls differed only moderately, but the night eaters had 9.3 eating episodes during the 24 hours, compared with 4.2 eating episodes for the control subjects. The subjects with bulimia nervosa averaged 6.2 eating episodes per day. Furthermore, the patterns of day and night intake differed dramatically for the two groups.

During the daytime, the cumulative energy intake of the night eaters lagged behind that of the control subjects, so that by 6 pm they had consumed only 37% of their total daily intake, while the controls had consumed 74% of their total daily intake. While the food intake of the controls slowed markedly by 8 pm, the night eaters did not decrease their eating until after midnight. From midnight to 6 am, the night eaters ate 56% of their energy intake, while the control group consumed 15%.

During the 24 hours, the average mood of the night eaters was lower than that of the controls. Also, after 4 pm, the mood of the night eaters fell hour by hour, while that of the controls remained unchanged. The night eaters also had far more nighttime awakenings than the control group (3.6 vs. 0.3, respectively) and more than half of the nighttime awakenings were associated with food intake. They ate mostly carbohydrates (73% of energy) during these awakenings. The ratio of carbohydrate to proteins in their nighttime snacks was 7:1.

Neuroendocrine study: differences in plasma cortisol, melatonin

The Tromsö researchers divided the 12 night eaters into 7 nonobese (mean body mass index, or BMI, 23.1) and 5 obese (mean BMI: 36) subjects. Just as in the behavioral study, nighttime awakenings were far more common among the night eaters than the controls (3.1 vs. 0.1).

All the night eaters, obese and nonobese alike, had lower plasma melatonin levels from 10 pm to 6 am than did controls. Plasma melatonin concentrations were higher in the obese control group than the normal-weight control group, but the concentrations were the same in the obese and nonobese night eaters. Plasma leptin levels were higher among the overweight subjects than among the normal-weight subjects in both night eaters and controls. The highest leptin concentrations did not differ between the obese and nonobese subjects.

Plasma cortisol was not significantly different between obese and nonobese subjects or controls. From 8 am to 2 am, plasma cortisol levels were higher among the night eaters than the controls. Preprandial and postprandial blood glucose and plasma insulin levels did not differ between the night eaters and controls in either the obese or normal-weight groups.

The carbohydrate-rich nighttime snacks (70.3% of kilocalories) and especially the high carbohydrate-to-protein ratio, suggest that night eating is designed to restore the disrupted sleep of the night eaters.

The night-eating syndrome also seems to differ from the “nocturnal sleep-related eating disorders reported by sleep disorder clinics and characterized by eating upon awakening from sleep, often due to sleepwalking and related sleep disturbances.

If this is a new syndrome, how can it be treated?

According to the authors, the presence of a sleep disorder linked to attenuation of the nighttime rise in melatonin suggests that exogenous melatonin may be helpful to these patients. Because the subjects’ ingestion of high-carbohydrate snacks may possibly be an attempt to improve sleep and mood by raising serotonin levels, selective serotonin reuptake inhibitors may also help. In addition, corticotropin-releasing hormone (CRH) receptor antagonists might be a helpful addition to psychotherapy.

All of these speculations will need careful clinical testing before any recommendations for treatment can be made.