In our society of 24-hour fast-food establishments and late-night marketing campaigns such as Taco Bell's “Fourthmeal: The Meal Between Dinner and Breakfast,” the idea of a “night eating syndrome” (NES) may seem odd. But for those whose sleep is interrupted and waistlines are growing, NES is a serious behavioral health concern.
NES was first described in 1955 by Albert Stunkard, MD, and colleagues as an eating disorder affecting the obese.1 They defined NES as involving the consumption of at least 25% of one's total daily caloric intake after the evening meal, the lack of morning appetite (termed “morning anorexia”), and initial insomnia (i.e., difficulty falling asleep). They noted a distinct pattern of depressed mood among those with NES that worsened during the day along with significant amounts of life stress.
Not until the late 1990s did NES receive more serious research and clinical attention. This was partly due to the interest in Dr. Stunkard's other clinical observation, binge eating syndrome, later renamed binge eating disorder.2,3 The notion that these behavioral phenotypes might play a role in the development of obesity for a subset of individuals intrigued researchers, leading to several interesting research studies.
Today, more than 50 years after the first medical report of NES, we know much more about its clinical characteristics, associated psychiatric comorbidities, and efficacious treatments.
Currently, NES is viewed as a circadian delay in the intake of food, but not sleep, and is manifested by (1) the consumption of 25% or more of one's total daily intake of food after the evening meal (termed “evening hyperphagia”), and/or (2) nocturnal awakenings accompanied with food ingestion. Persons with NES are aware of their nighttime eating, as opposed to those diagnosed with the parasomnia, nocturnal sleep-related eating disorder (NSRED); these patients also consume food in the middle of the night, but do so while still asleep.4 Once considered crucial to a NES diagnosis, depressed mood and morning anorexia now are considered associated features, but are neither necessary nor sufficient for diagnosis.
Many healthcare providers and the public assume that persons diagnosed with NES eat regularly during the day and consume an extra meal at night, similar to Taco Bell's Fourthmeal concept. Yet this does not appear to be the case for most patients diagnosed with NES. In studies night eaters consume a similar amount of calories during the course of a day as controls, but the pattern of food intake differs greatly. O’Reardon and colleagues found that night eaters, compared with controls, consumed less food during the first third of the day (often skipping breakfast), equal amounts of food during the middle part of the day, and more food during the last eight hours of the day.5 In support of the idea that NES is a circadian shift in food consumption, but not sleep, they noted that night eaters reported the same time of sleep initiation, sleep termination, and total sleep duration as controls.
Contrary to popular lore, NES research has not supported the notion that night eaters consume vastly greater amounts of carbohydrates during the nighttime hours. In an inpatient study of the circadian eating and neuroendocrine features of NES, Allison and colleagues found that night eaters consumed twice the carbohydrates, twice the protein, and four times the amount of fat during the nighttime hours, compared with weight-matched controls.6 These findings likely reflect night eaters’ desire for a quick, tasty treat (that is often high in fat) rather than carbohydrates per se.
Prevalence of NES
The prevalence of NES varies widely, depending on the population under study and on the diagnostic criteria used to classify it. The best prevalence estimate of NES in the general population is 1.5%.7 The prevalence of NES rises dramatically among the obese, with prevalence rates of about 9%.8 Prevalence does not appear to differ by gender or ethnicity and, although rarer, NES does occur among nonobese persons.
In a recent collaborative study between the University of Pennsylvania and the University of Minnesota, my colleagues and I estimated the prevalence of NES among patients seeking psychiatric services in university-based outpatient treatment clinics.9 Patients were being treated for a variety of psychiatric conditions, including depression, bipolar disorder, anxiety, schizophrenia, substance use, and personality disorders. The prevalence of NES was surprisingly high, with 12.3% of the sample meeting criteria based on a comprehensive telephone interview. Obese patients, regardless of psychiatric diagnosis, were five times more likely to meet criteria for NES than nonobese patients. These findings not only confirmed our hypothesis that night eating is associated with greater psychiatric comorbidity, but once again showed that night eating is associated with obesity.