OBJECTIVE: The main aim of this study was to identify subjects with (1) night eating syndrome (defined as morning anorexia, evening hyperphagia and insomnia) and (2) nocturnal eating syndrome (defined as eating at night after having gone to bed). In the literature the differences and similarities between these two syndromes are not clear.
SUBJECTS: One-hundred and ninety-four obese patients from an academic, clinical obesity unit. Mean BMI (±s.d.) was 40±5 kg/m2, age 44±12 y and 76% were women.
MEASUREMENTS: Questionnaires with multiple choices and open questions along with the Binge Eating Scale.
RESULTS: Fourteen percent of the patients met the criteria for night eating and/or nocturnal eating syndrome. Night eating syndrome was manifest in 6% of the patients and nocturnal eating syndrome in 10%. Both the night eaters and the nocturnal eaters had more trouble getting to sleep than the patients without night/nocturnal eating problems (P<0.001 and P<0.01). The nocturnal eaters also had more trouble staying asleep (P<0.001). Morning anorexia was not typically found in nocturnal eaters. Being on long-term sick leave was more common among the nocturnal eaters (P<0.01).
CONCLUSION: Fourteen percent of the patients at our obesity unit met the criteria for night eating and/or nocturnal eating syndrome. There are clear similarities between night eating syndrome and nocturnal eating syndrome, but also differences.
In 1955 Stunkard et al first described night eating syndrome.1 During the 45 y since then, few studies have been performed on the subject and many questions regarding the syndrome remain unanswered.
The three criteria for ‘night eating syndrome’ defined by Stunkard in 1996, are: morning anorexia, that is no appetite for breakfast, evening hyperphagia, defined as 50% or more of food intake after 7 pm and insomnia, ie trouble getting to sleep and/or staying asleep.2 This definition of night eating syndrome, or derivations of it, has been used in several studies.3,4,5,6,7,8 A summary of the major prevalence studies performed, indicates that the frequency of night eating syndrome varies from 8 to 27% among obese patients (Table 1). The study performed by Stunkard in 19551 is an exception, where 16 patients out of 25 (64%) met the criteria for night eating syndrome.
In 1990 ‘nocturnal eating syndrome’ was described by the American Sleep Disorders Association in the International Classification of Sleep Disorders. The definiton of this syndrome is: ‘Frequent and recurrent awakenings to eat and normal sleep onset following ingestion of the desired food’.9 This definition has also been used in some studies.10,11,12 Such studies suggest that there is little difference in the occurrence of the two syndromes (Table 1).
Thus both night eating syndrome and nocturnal eating syndrome have clear definitions. In the literature though, the differences between the two syndromes are not always clear. In some articles the terms night eating and nocturnal eating are used synonymously.12,13,14 In the International Classification of Sleep Disorders, night eating is given as synonymous with, and as a key word to, nocturnal eating.9
The fact that night eating is something the obese patients at our clinic rarely talk about, and the limited knowledge in the literature, made us realize that our knowledge about this problem is rather poor. Therefore our main aim in this study was to clarify whether or not night eating is a problem to consider in group treatment at our clinic, or if it very rarely occurs among our obese patients, and to clarify whether we have to deal with two different syndromes or just one. This task was achieved by identifying subjects with night eating syndrome as well as subjects with nocturnal eating syndrome among the patients at our obesity unit.
The second aim was to obtain further knowledge of the two syndromes as a base for future research, in particular with regard to potential clinical and therapeutical consequences.
In order not to exclude any kind of night eating behaviour at this early stage of our research we chose to construct a self-report questionnaire including questions about both the night eating syndrome and the nocturnal eating syndrome (Appendix, questions 1–13).
The definition of night eating used in this study is Stunkard's definition: morning anorexia, evening hyperphagia and insomnia.2 These criteria, however, do not seem to have been formally validated. We have defined morning anorexia as ‘no appetite in the morning’, evening hyperphagia as ‘the largest food intake occurring during a time period after 7 pm’ and insomnia as ‘trouble getting to sleep and/or staying asleep’. The criteria we used for the definition of nocturnal eating were ‘waking up at night and getting out of bed to eat’ and/or ‘after having gone to bed, getting out of bed to eat or eating in bed’.
One-hundred and ninety-four obese patients, referred to our obesity unit, answered the questionnaire. We excluded all patients working night shift/night time since it is known that shift work can cause a redistribution of food intake from day to night.15
In addition, patients participating in our day care hospital program during the period of April 1998 to March 1999 answered open questions about food choices as well as multiple choice questions about whether or not they considered themselves night eaters (n=104) (Appendix, questions 14–17). Since January 1998 our day hospital program evaluation has included several behavioural and psychological questionnaires. We have compared the results of the Binge Eating Scale16 (translation into Swedish: K Franson) with those defined as nocturnal eaters and the obese patients in the day care hospital program.
The information on frequency of sleeping problems and smoking habits among normal weight subjects has been taken from Statistic Sweden, a data base of 8935 subjects (Living conditions 96/97, Statistic Sweden, unpublished data).
We used SPSS and Statistica for statistical analysis. For patient data and differences between the groups, we used the chi-square test, Fisher's exact test, the Mann–Whitney U-test and the independent samples t-test. For correlation between night eating and morning anorexia we used Spearman's rank correlation coefficient. The study was approved by the Hospital Ethical Committee.
The subjects in this study had a BMI of 40±5 kg/m2 (mean±s.d.) and age 44±12 y. Seventy-six percent were women (n=147) and 24% were men (n=47).
Prevalence of night eating and nocturnal eating syndrome
Thirty-three percent of the patients at our obesity unit had morning anorexia, 31% had evening hyperphagia and 46% had insomnia (Figure 1). A combination of all three criteria, ie night eating syndrome was found in 6% (Night). Nocturnal eating syndrome (Nocturnal) was manifest in 10% of the subjects. When using both the definition of night eating and the definition of nocturnal eating syndrome we found that 14% met the criteria of one or both of the two syndromes. Among the group of the 19 Nocturnal, five subjects met the criterion ‘waking up at night and getting out of bed to eat’, six subjects met the criterion ‘after having gone to bed, getting out of bed to eat or eating in bed’ and eight subjects met both criteria.
When asking the question ‘Do you think that you have problems with night eating?’ we found that 67% of the whole group answered yes for the time period 7–10 pm and 14% answered yes for the time period after 10 pm (n=105). All Nocturnal and all Night but one, claimed that the night eating had contributed to their obesity.
Forty-six percent of the patients at our clinic stated that they had sleeping problems, which is significantly more than the 15% among normal-weight Swedish people (P<0.001) (Living conditions 96/97, Statistic Sweden, unpublished data).
The prevalence of insomnia was significantly higher among Nocturnal (n=19) compared with the other obese patients (Other; n=167, Table 2). More Nocturnal had trouble getting to sleep, 63% vs 29% (P<0.01) and more Nocturnal had trouble staying asleep, 74% vs 31% (P<0.001). Among Night (n=11) more patients had trouble getting to sleep, 100% vs 29% (P<0.001), but there was no difference in prevalence of trouble staying asleep.
The frequency of morning anorexia did not differ between Nocturnal and Other, and we did not find a statistically significant correlation between eating late at night (7 pm to 4 am) and morning anorexia.
Significantly more Nocturnal than Other were on long-term sick leave, 32% vs 8% (P<0.01), which was not the case for Night. We found no differences regarding occupation or civil status. Among Night as well as Nocturnal and Other, the majority were gainfully employed or students. The patients who were not gainfully employed or students were retired, unemployed, on parental leave or on a long-term sick leave. Among all patients (Night, Nocturnal, Other) about a third were single or a single parent (36/37/31%), while the majority lived with another adult (64/63/69%).
We found no difference in gender or BMI between the groups. There was no difference in age between the Nocturnal and Other. Night were younger than Nocturnal and Other, 36 vs 44 y (P=0.0293). Among both Nocturnal and Night, as well as among Other, smoking was as common as among Swedish people in general: smoking daily about 20%, smoking sometimes about 10%, nonsmokers about 70% (Living conditions, Statistic Sweden, unpublished data).
Critical time periods
The answers to the question ‘When during day and night is it usually hardest to refrain from something you feel like eating?’ show that the most difficult period to refrain from eating is from 7 to 10 pm (Figure 2 a and b). Over 60% of both Nocturnal, Night and Other had difficulties during this period. The majority of Nocturnal (58%), and of Night (55%) also had difficulty refraining from eating between 10 pm and 1 am, compared to only 18% among Other (P<0.001 and P=0.0101). There was also a significant difference between Nocturnal and Other, between 1 and 4 am, 26% vs 0.6% (P<0.001) and between 4 and 7 am, 11% vs 0.6% (P<0.05). No Night claimed to have any problem refraining during this time period.
In the morning and until the early afternoon, from 7 am to 4 pm, there was no difference between the groups. Until 4 pm the majority did not have great difficulty refraining from eating. Between 4 and 7 pm fewer patients among Night had problems refraining compared to Other, 9% vs 48% (P<0.05).
According to the results of the Binge Eating Scale, Night and Nocturnal had binge eating problems to the same extent as Other, median score 22 (range 13–31) vs median score 18 (range 1–37).
The most commonly selected food item at night was sandwiches, chosen by 50% of the subjects (Table 3). There was no difference between Night and Nocturnal and Other regarding food choices at night, but we did find a gender difference. More men than women chose alcoholic beverages at night, 29% vs 3% (P<0.001) and women tended to choose chocolate to a greater extent, 10% vs 0% (P=0.074).
This study is based on a rather short, self-report questionnaire that we constructed and which is not yet properly validated. This is an obvious weakness of the study. The questionnaire was first tested in a smaller group of patients (40 patients not included in the study) and thereafter reconstructed. A strength of the study is that all patients who were asked to answer the questionnaire did so. Answering the questionnaire was totally voluntary and did not in any way affect the patient's treatment. (The person asking the patients to answer the questionnaire was not a member of the treatment team.)
Compared to other studies (Table 1) we found a rather low frequency of night eating syndrome among our patients (6%). One reason for this might be a question of interpretation of Stunkard's definition of the syndrome. For example, evening hyperphagia, defined by us as ‘the largest food intake occurring during a time period after 7 pm’ was defined by Rand et al as ‘excessive evening eating’5 and by Kaldau et al as ‘eating on and off throughout the evening without enjoyment’.4 We also believe there is a cultural explanation. In Sweden, dinner is served earlier than in many other countries. For the majority of the Swedish people dinner time is around 6 pm (A Marmur, E Callmer, L-E Holm, G Wilsby, Applied Nutrition, unpublished data). This is probably why only 20% of the patients at our unit claimed that they had a food dish after 7 pm, when answering the question ‘What do you usually eat at night?’ A study by Adami et al showed that in Italy, a country with a Mediterranean eating style, 70% of the people had dinner after 8 30 pm.17
The nocturnal eating syndrome was found in 10% of the subjects. This is a sleep-related eating disorder, not related to any specific time of night. When both definitions were used together we found a total group of 27 patients (14%). Perhaps this number is closer to the true picture of the night eating problem among the obese patients. In addition, the answers to the question ‘Do you think that you have problems with night eating?’ support the idea that night/nocturnal eating is not uncommon (67% for the time period 7 to 10 pm and 14% for the time period after 10 pm). Thus even for Other, the time period between 7 and 10 pm is a period when it is difficult to refrain from eating. This is important to keep in mind when discussing changes of food habits with the patients.
Nearly 50% of the patients at our clinic had sleeping problems of some kind. Among the Night and Nocturnal the problem was even more common. This suggests that there is a need for greater awareness of the importance of sleeping problems in the design of the obesity unit's routines for diagnosing and managing obese patients.
In obesity treatment we find it important to note gender differences when discussing food choices with the patients. In this group, more men than women consumed alcoholic beverages in the evening, while women tended to choose chocolate to a higher extent. In a former study at our unit we also found gender differences in food preference; men chose alcoholic beverages more often than women did and women chose sweets more often than men did.18 We also found that sandwiches were perceived to have contributed to the development of obesity by 40% of the patients at our unit. In the present study sandwiches were the most commonly chosen food item at night among the obese patients. Sandwiches are common in Swedish diet19 and obese men were found to have a higher energy intake from sandwiches than normal-weight men.20 Our data on night eating supports the notion that sandwiches are a great problem to our patients, which has to be taken into consideration when giving advice on food choices. Only 30% of the subjects mentioned a drink when answering the question about what they consume at night. Our clinical experience is that patients tend to forget what they drink with the food, for example with the evening sandwiches.
Not more than 37% of Nocturnal in this study experienced morning anorexia. This implies that by using Stunkard's definition of night eating we exclude the majority of the nocturnal eaters in this group.
On the other hand, the definition of nocturnal eating used in this study includes some patients who may not have a very high energy intake at night. The nocturnal eating syndrome refers to an eating pattern rather than to the amount of food consumed. Therefore, in some cases, nocturnal eating might not be a main problem in the caloric balance.
Our results support earlier statements that night eating syndrome needs to be considered in treatment of obesity.21 Even though we found that many features, such as BMI and frequency of binge eating among the Night/Nocturnal did not differ from Other, we have reached the conclusion that, at our unit, there seems to be a need for special treatment for obese patients with night eating problems. To start a treatment program for obese patients with night/nocturnal eating problems, more research is needed both on how to diagnose patients with the syndrome(s) and more knowledge about the syndrome(s) itself. A correct diagnosis of night/nocturnal eating is a condition for specialized treatment. For diagnosing we believe it is important to develop a questionnaire or an interview format with a limited number of questions that can be managed in clinical routine.
Our clinical experience is that talking about nocturnal activity is a sensitive issue and that eating in the dark can be a very shameful activity, which is not easily admitted. To find out more about this behaviour and to find answers to the questions why?, when?, how? what?, we believe the open interview is an appropriate method, which will also be the next step in night eating research at our unit. There is also a need for futher research on observation of sleep and eating relationships in a laboratory setting with neuroendocrine measures, which so far has been performed only in one study.8
Night eating and nocturnal eating patterns have clear similarities, but also show differences in appearence. Our opinion is that there is more to unite the two syndromes than there are differences between them. The majority of these patients had sleeping problems; it was significantly harder for them to refrain from eating later at night and all but one claimed that their eating at night had contributed to their obesity. We believe that the differences between the groups found in this study are not wide enough to cause any trouble in a joint treatment program.
By including both night and nocturnal eating syndrome in one criterion, we believe that there would be improved chances of an effective treatment program by an increased cooperation between clinics specialized in obesity, eating disorders and sleeping disorders. We also believe that by using two separate criteria there would be a greater risk of some patients being excluded even though they may have night eating problems.
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This study was supported by grants from Resource Center for Eating Disorders.
Eating and Sleeping habit Questionnaire
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Cerú-Björk, C., Andersson, I. & Rössner, S. Night eating and nocturnal eating—two different or similar syndromes among obese patients?. Int J Obes 25, 365–372 (2001). https://doi.org/10.1038/sj.ijo.0801552
- food selection
- night eating
- nocturnal eating
- sleeping problem
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