This is the first weight controlled study to characterize fully the circadian distribution of food intake and the psychosocial correlates of NES among non-obese adults. These findings show that NES is associated with an abnormal circadian pattern of food intake, disordered eating attitudes and behaviors, mood and sleep disturbance, elevated perceived stress, decreased quality of life, and greater likelihood of Axis I psychopathology. They support the clinical significance of this diagnosis, independent of the presence of obesity.
Several of this study’s findings are worthy of further discussion, including its replication of previous research showing increased Axis I psychopathology among night eaters. Similar to a recent study by de Zwaan and colleagues (2006)
, NES was associated with increased rates of unipolar mood disorders and anxiety disorders. Previous research has found increased rates of NES among persons diagnosed with substance use disorders (Lundgren et al., 2006
). This was the first study to find increased rates of substance use disorders among persons with a primary complaint of night eating syndrome, suggesting the co-occurrence of these disorders is bi-directional.
Although the rates of co-morbid mood, anxiety, and substance use disorders are high among this NES group, the abnormal eating pattern exhibited by the NES group cannot be accounted for by these co-morbidities. Specifically, there were no differences in the degree of evening hyperphagia, nocturnal awakenings, or nocturnal ingestions of food for night eaters with and without lifetime unipolar mood disorders, anxiety, disorder, or substance use disorders. Similarly, when controlling for BDI scores, most of the analyses between groups remained significant, including the global scores of the PSQ and EDE, EI Cognitive Restraint, Hunger, and Disinhibition, as well as the percentage of evening hyperphagia, frequency of nocturnal awakenings, and frequency of nocturnal ingestions of food (data available upon request).
As would be expected, the delay in the circadian pattern of eating among night eaters was highlighted with the cumulative food intake curves and the survival analysis. As the diagnostic criterion we used for evening hyperphagia was at least 25% of food consumed after the evening meal, we used time to consumption of 75% of intake to compare the groups. The four-hour delay highlights the extent of the circadian differences between the groups in respect to eating, further suggesting that NES is clinically significant among the non-obese.
The nearly 400 calorie difference in total daily food intake between night eaters and controls () raises additional questions, such as the potential role of compensatory behaviors in NES and for weight gain over time. It is apparent, with 50% of total daily intake consumed after the evening meal, that these non-obese night eaters must be restricting food intake during the day. While part of this may be due to lack of hunger upon awakening in the morning, many did not eat anything until the afternoon, and some did not eat until the evening meal. Longitudinal research is necessary to determine if NES leads to weight gain over longer periods of time and whether compensatory behaviors, such as excessive exercise and caloric restriction (successful or unsuccessful), accounts for weight maintenance among those who do not gain weight over time.
NES among non-obese persons appears to share commonalities with the traditional eating disorders, such as increased rates of mood, anxiety, and substance use disorders. Not all non-obese night eaters, however, experience these co-morbid disorders; future studies should assess co-morbid Axis II disorders as well.
Limitations of this study include the small sample size and the possibility that persons responding to recruitment advertisements may have higher levels of psychopathology than persons with NES in the community who did not respond. Despite the small sample size, most comparisons were statistically significantly different, even upon adjustment with the Holm-modified Bonferroni.
In conclusion, these results are the first to describe the degree and breadth of negative psychosocial correlates of NES among non-obese persons in comparison to a weight matched control group. These findings complement the Birketvedt et al. (1999)
and Marshall et al. (2004)
reports showing that non-obese night eaters are not clinically different from obese night eaters. The current findings, however, make clear that nighttime eating behavior among non-obese persons is not benign, even though obesity does not constitute a problem. To the contrary, the current findings show that regardless of BMI, NES is associated with pathological eating attitudes, mood and sleep disturbance, and co-morbid psychopathology.