Definitions of Night Eating in Adolescent Girls

Transcription

1 Definitions of Night Eating in Adolescent Girls Ruth H. Striegel-Moore,* Douglas Thompson, Debra L. Franko, Bruce Barton, Sandra Affenito, George B. Schreiber, and Stephen R. Daniels** Abstract STRIEGEL-MOORE, RUTH H., DOUGLAS THOMPSON, DEBRA L. FRANKO, BRUCE BARTON, SANDRA AFFENITO, GEORGE B. SCHREIBER, AND STEPHEN R. DANIELS. Definitions of night eating in adolescent girls. Obes Res. 2004;12: Objective: To describe the prevalence of night eating in a community cohort of black and white girls, using different definitions of night eating as described in the literature. Research Methods and Procedures: Three-day food diaries collected as part of the National Growth and Health Study were examined to identify episodes of night eating, which was defined in five different ways: eating 25% of daily caloric intake after the last evening meal, eating 25% of daily caloric intake after 7 PM, eating 50% of daily caloric intake after the last evening meal, eating 50% of daily caloric intake after 7 PM, or eating between 11 PM and 4:59 AM. Results: Frequency of night eating varied tremendously depending on how the behavior was defined. For the least restrictive definition ( 25% of total intake after last meal), 50% to 70% of girls reported one night eating event; for the most restrictive ( 50% of total intake after last meal), only 1.5% of 11-year-old girls diaries and 3.5% of 19-year-old girls diaries contained a night eating event. The frequency of night eating decreased dramatically (typically by a factor of 10) if the inclusion criteria required multiple night eating events in a given week. Discussion: A standard definition of night eating behavior is needed to advance the field. An agreed-on operationalized Received for review October 28, Accepted in final form June 8, According to U.S. code, all journals requesting payment of author page charges in order to defray the cost of publication are required to publish a disclaimer. This article must, therefore, be marked advertisement in compliance with U.S.C. Section 1734 solely to indicate this fact. *Department of Psychology, Wesleyan University, Middletown, Connecticut; Maryland Medical Research Institute, Baltimore, Maryland; Department of Counseling and Applied Educational Psychology, Northeastern University, Boston, Massachusetts; St. Joseph s College, West Hartford, Connecticut; Westat, Inc., Rockville, Maryland; and **Department of Cardiology, Cincinnati Children s Hospital, Cincinnati, Ohio. Address correspondence to Ruth H. Striegel-Moore, Department of Psychology, Wesleyan University, 207 High Street, Middletown, CT rstriegel@wesleyan.edu Copyright 2004 NAASO definition that includes time of day, amount of calories consumed, and a frequency criterion would enable crossstudy comparisons and encourage the examination of developmental and clinical considerations of night eating behavior. Key words: night eating, eating disorder Introduction The night eating syndrome (NES) 1 was introduced into the medical literature in 1955 by Stunkard et al. (1), based on their clinical observations of eating disturbances in a group of morbidly obese patients seeking treatment for weight control. Stunkard and colleagues (1) distinguished two distinct eating patterns, night eating and binge eating, which they believed could contribute to an understanding of the etiology of obesity. Although binge eating has been studied extensively, little research has focused on night eating. Research is now beginning to examine the possibility that, like binge eating, night eating may contribute to obesity (2). As discussed in a comprehensive review of the literature by de Zwaan et al. (3), to date, no uniform definition of NES has been adopted. Indeed, neither the behavioral components (morning anorexia and evening hyperphagia) nor the sleep or mood disturbance criteria (1,4) have been operationalized consistently across studies. The definitional variations may explain, in part, why the literature has produced inconsistent findings regarding the prevalence of NES and its demographic (e.g., gender) and clinical (e.g., obesity) correlates (3). Evening hyperphagia originally was considered to be the main criterion for, and now is common to all definitions of, NES. Basically, evening hyperphagia implies that the amount of food consumed is excessive given the time of day when the eating episode occurs. However, definitions vary in terms of the amount of food consumed, the time frame 1 Nonstandard abbreviations: NES, night eating syndrome; NHLBI, National Heart, Lung, and Blood Institute; NHGS, National Growth and Health Study; NCC, Nutrition Coordinating Center; GEEs, generalized estimating equations. OBESITY RESEARCH Vol. 12 No. 8 August

2 involved, and whether the evening meal ( dinner ) is included when defining the amount of food consumed after the specified time of day (3). The criteria for amount of food consumed vary from a low of 25% of daily caloric intake (1) to a high of 50% or more (5). In some studies, these amounts include the food consumed as part of dinner (5), whereas in other studies, the food consumed as part of the last meal of the day is not counted toward the caloric intake criterion (6,7). Because of the concern about the validity of dietary intake data, some investigators have proposed a definition that does not rely on a particular percentage of daily caloric intake but requires that the largest food intake occur after 7 PM (8,9). In some studies, evening time is defined as after 7 PM (10); in other studies, to accommodate the considerable cultural variations regarding the timing of dinner, no specific time is defined, and instead, the definitions simply focus on caloric consumption after dinner (11). Not surprisingly, each of these definitional decisions has a major impact on how many individuals meet criteria for evening hyperphagia and the calories consumed during evening hyperphagia episodes. For example, one study reported that calories consumed after 6 PM including dinner averaged 63% of daily caloric intake; in contrast, when excluding dinner, the average caloric intake was only 33.5% (12). We further note that the definition of last evening meal is ambiguous in that it relies on the respondent s assessment of whether an eating episode was a meal. Finally, although it is implied that the behavioral pattern occurs with some regularity, few studies describe a frequency criterion of evening hyperphagia. Thus, it is unclear what minimum average frequency of evening hyperphagia is needed for a diagnosis of NES. Given the central role of this behavior to the definition of NES, we believe that the scientific study of NES will be advanced by considering the methodological issues involved in the measurement of evening hyperphagia and offering basic epidemiological data for the four most commonly used definitions of evening hyperphagia and for a simple, objective definition introduced in this study. Similar to research of binge eating, where experts have moved from initially fairly general definitions to operationalized criteria that make explicit reference to statistical norms, research of NES will benefit from a clearer specification of night eating that is informed by the distribution of the behavior in the population. Specifically, the overeating part of the current definition of binge eating invokes an explicit reference to normative behavior: eating an amount that is larger than what most people would consume under similar circumstances (13). For night eating, one might invoke an explicit reference to time of day when the eating occurred that should be later than when most people would eat under similar circumstances. One might also add a calorie criterion, as has been advanced by others (1,5), and adopt a uniform use of these criteria to permit comparisons across studies. Such norm-based definitions would require population-based data regarding the behavior of interest. We are not aware of any community-based studies of night eating. To advance the knowledge of night eating, we took advantage of the availability of data that were collected as part of a large epidemiological study of risk factors for cardiovascular disease, the National Heart, Lung, and Blood Institute (NHLBI) Growth and Health Study (NGHS) (14). A major aim of the present report was to provide detailed descriptive information on night eating in girls 9 to 19 years old. Because of the exploratory nature of this study, multiple definitions of night eating were used, including four that were based on operationalized definitions advanced in previous studies of NES and a fifth that was introduced for the purpose of this study because of its relatively simple and, therefore, possibly more reliable, measurement (see Research Methods and Procedures ). For each definition, we examined the frequency of night eating in our sample by age group. We hypothesized that, regardless of the particular definition specified, night eating would be more common as the girls got older. We also expected that the more restrictive definitions (e.g., consuming 50% or more of daily caloric intake after dinner or eating after 11 PM) would be least common, and the most inclusive definition (i.e., eating 25% after 7 PM) would be most common. We further sought to characterize night eating in terms of the total caloric content and the percentage of total daily caloric intake of night eating episodes, the macronutrient content of night eating episodes, and the average number of episodes per night. Finally, we examined demographic correlates of night eating and explored the relationship between night eating and childhood overweight. Given conflicting findings in the literature, we did not specify a hypothesis regarding the association of night eating with childhood overweight. Research Methods and Procedures Participants and Recruitment As previously reported (14), the NGHS recruited 2379 black and white girls who were 9 or 10 years old at study entry at three clinical centers: University of California at Berkeley, University of Cincinnati/Cincinnati Children s Hospital Medical Center, and Westat, Inc./Group Health (Rockville, MD). The Berkeley site recruited participants from public and parochial schools in the Richmond Unified School District. The area was chosen based on census tract data showing approximately equal percentages of black and white children with the least degree of income disparity between the ethnic groups. Cincinnati recruited girls from all public and parochial schools in greater Cincinnati to have ethnic and socioeconomic representation for Hamilton County (which includes inner city, urban, residential, and suburban areas). The Westat cohort was randomly drawn 1312 OBESITY RESEARCH Vol. 12 No. 8 August 2004

3 from a membership listing of families who were enrolled in a large Washington, DC area health maintenance organization and, because the membership did not include a sufficient number of white families with age-eligible girls, from several local Girl Scout troops in the same geographic area. Eligible participants identified themselves (using census categories for race/ethnicity) as black or white, non- Hispanic, and with ethnically concordant parents or guardians. All girls who entered the NGHS had assented, and their parents had consented to their participation. On average, the black households had lower family incomes and lower educational levels than the white households. Nevertheless, in each ethnic group, wide ranges of income ( $10,000 to $75,000) and educational levels (less than high school diploma to graduate degree) were represented. Due to variable annual participation rates, sample sizes varied from visit to visit. Retention rates were very high at visits 2 to 4 (96%, 94%, 91%), declined to a low of 82% at visit 7, and increased to 89% at visit 10. Diaries covering fewer than 3 days (3.9%) were excluded to ensure that every diary had the same number of days to observe night eating. Instruments and Procedure A complete description of NGHS procedures and measures has been reported (14). Briefly, data were collected annually at participating sites or, if the girl was unable to attend the site, at her home. Only instruments of relevance to the present report are described below. Demographic Information. Ethnicity (black or white) was defined by the participants self-report at baseline. For the present report, parental education was categorized as 4 or more years of (1) vs. less than 4 years of (0). Education was chosen over income as a proxy of socioeconomic status, in part, because NGHS data were collected at three distinct geographic locations in the United States with different average household income and different price indices (i.e., the same amount of income has different purchasing power in Cincinnati compared with Washington, DC). Also, previous studies have shown that education is a better predictor of health-related outcomes than income (15 17). Participants age was recorded as age at last birthday. Height and Weight. Annually, research staff measured the girls height and weighed the girls (all visits). Childhood overweight was determined by calculating BMI [weight in kilograms divided by height in meters squared (2)] and using age-specific cutoff points from National Health and Nutrition Examination Survey III (18), defining overweight as at or above the age-specific 95th percentile of BMI for women (0, not overweight; 1, overweight). Dietary Assessments. Three-day food records that had been previously validated compared with observed intakes during school lunch (19) were collected annually for visits 1 to 5 and then again at visits 7, 8, and 10. For each year that the diet records were collected, dietitians used age-appropriate materials (ruler, measuring cups and spoons, and a booklet with pictorial instructions and food record pages) to instruct girls to record all food and drink, type of meal (breakfast, snack, lunch, etc.), and time of intake for 3 consecutive days that included 2 weekdays and 1 weekend day. Dietitians, trained and certified by the University of Minnesota Nutrition Coordinating Center (NCC), reviewed the completed food records individually with the girls. Supplementary information was not sought from parents because confidentiality was given a higher priority than additional details on foods or food preparation. Standard probes were used to respond to girls questions and to clarify incomplete responses. Default values adapted from NCC were used for missing information on food amounts, types, and preparation methods. To minimize the use of defaults, NGHS dietary staff had a notebook of labels and label pictures to help girls describe foods. Beginning in year 3, dietitians rated the eating episodes as meals or snacks. Food records were coded and analyzed for nutrients using Food Table Version 19 of the NCC nutrient database (20). For girls exhibiting recurrent night eating, the average total calories consumed at night and the percentage of total daily calories consumed at night were calculated. The percentage of calories consumed at night from protein, carbohydrates, and fats was also calculated. Basic concepts related to night eating were operationalized as follows. The food diaries covered 3 calendar days (from midnight to 11:59 PM). When examining night eating, it seems appropriate to group the late evening hours of 1 calendar day with the early morning hours of the next calendar day (i.e., a girl who eats at 11 PM on 1 calendar day and then again at 1 AM of the next calendar day has both of these eating episodes on the same day ). Therefore, day was operationalized as the 24-hour continuous period beginning at 5 AM and ending at 4:59 AM of the next calendar day. Only 2 such complete days were covered in a 3-day food diary: 5:00 AM on the 1st food diary day until 4:59 AM on the 2nd food-diary day, and 5:00 AM on the 2nd diary day until 4:59 AM on the 3rd diary day. Only the information from these 2 days was used in the analyses reported in this paper. For definitions based on consumption after 7 PM, night was the period beginning at 7:01 PM and ending at 4:59 AM on the following calendar day. For definitions involving consumption after dinner, night began immediately after dinner and lasted until 4:59 AM of the next calendar day. For definitions involving consumption after 11 PM, night began at 11:01 PM and ended on 4:59 AM on the following calendar day. Five definitions of night eating were considered: eating 25% or more of the daily caloric intake at night, after dinner; eating 50% or more of the daily caloric intake at OBESITY RESEARCH Vol. 12 No. 8 August

4 Table 1. Sample sizes and the percentage of girls exhibiting night eating on 1 or 2 days, for five definitions of night eating Definitions involving dinner Definitions based on time 25% kcal after dinner (%) 50% kcal after dinner (%) 25% kcal after 7 PM (%) 50% kcal after 7 PM (%) Any eating after 11 PM (%) n 1 day 2 days 1 day 2 days* n 1 day 2 days 1 day 2 days 1 day 2 days 9 NA NA NA NA NA NA NA NA NA NA At study entry, one-half of the girls were 9 or 10 years of age, respectively. Ratings of eating episodes as dinner were not available in the first 2 years. NA, not applicable. * Insufficient sample size for statistical tests. Not statistically significant. Main effect of age, p Main effect of age, p night, after dinner; eating 25% or more of the daily caloric intake at night, after 7 PM; eating 50% or more of the daily caloric intake at night, after 7 PM; and any eating at night of any amount after 11 PM and before 5 AM on the following day. In the analyses describing various characteristics of night eating (e.g., caloric intake), the behavior needed to be present in both days captured in the food diary. Dinner. Some definitions of night eating refer to the evening meal or dinner. Beginning in visit 3, each eating episode in the food diaries was rated as a meal or snack by NCC dietitians. Dinner was defined as the last dietitianrated meal occurring between 5 and 8:59 PM on a given day. After dinner was defined to include any eating that occurred after dinner but before 5:00 AM on the following day. For the first and second visits, it was not possible to categorize night eating when meal was involved in the definition. Data Analysis Because the analyses involved repeated measures within girls, statistical tests were conducted with generalized estimating equations (GEEs), which appropriately account for the nonindependence of observations at different times within girls. The GEE analyses were conducted with PROC GENMOD in (SAS Institute, Inc., Cary, NC). Because multiple significance tests were performed, a conservative significance level of p 0.01 was adopted. Results Prevalence of Night Eating Table 1 shows the percentage of girls at each age who reported night eating during none, 1, or 2 days, using the five different definitions of night eating. The sample sizes were smaller for the definitions involving dinner because meal classifications were not available for the first two visits (when most girls were 9 to 11 years old). For all definitions, the sample sizes also varied because food diaries were not collected in visits 6 and 9 (when most girls were 14 to 15 and 16 to 17 years old, respectively) or due to missing data. As expected, eating 25% of total daily caloric intake after 7 PM (the least restrictive definition of night eating) was quite common, with just over 50% of 9-year-old girls and 70% of 19-year-olds reporting at least one night eating episode in their food diaries. When keeping the same time criterion but adopting the more restrictive caloric requirement of 50% or more of daily intake, rates of night eating 1314 OBESITY RESEARCH Vol. 12 No. 8 August 2004

5 Table 2. Mean (SD) and selected deciles (10th percentile/50th percentile/90th percentile) of number of night eating episodes per day in which night eating occurred, by definition of night eating Definition of recurrent night eating: eating on 2 days 25% of total kcal in day 50% of total kcal in day Any eating after 11:00 PM* (1.0), 1.0/1.5/3.0, n (1.2), 1.0/1.5/4.0, n (0.0), 1.0/1.0/1.0, n (1.1), 1.0/1.5/3.0, n (0.7), 1.0/1.5/2.5, n (1.2), 1.0/1.3/4.0, n (0.9), 1.0/1.5/2.5, n (1.1), 1.0/2.0/3.0, n (0.6), 1.0/1.0/2.0, n (0.9), 1.0/1.5/2.5, n (0.9), 1.0/1.5/3.0, n (0.3), 1.0/1.0/2.0, n (0.6), 1.0/1.5/2.5, n (0.5), 1.0/1.5/2.5, n (0.4), 1.0/1.0/2.0, n (0.7), 1.0/1.5/2.5, n (0.7), 1.0/1.0/2.5, n (0.3), 1.0/1.0/1.5, n (0.7), 1.0/1.5/2.5, n (0.6), 1.0/1.5/2.5, n (0.4), 1.0/1.0/2.0, n (0.6), 1.0/1.5/2.5, n (0.8), 1.0/1.5/3.0, n (0.4), 1.0/1.0/2.0, n (0.7), 1.0/1.5/2.5, n (0.8), 1.0/1.5/2.5, n (0.3), 1.0/1.0/1.5, n (0.7), 1.0/1.5/2.5, n (0.9), 1.0/1.5/3.0, n (0.4), 1.0/1.0/1.5, n (0.7), 1.0/1.5/2.5, n (0.8), 1.0/1.8/3.0, n (0.4), 1.0/1.0/2.0, n 48 At study entry, one-half of the girls were 9 or 10 years of age, respectively. * Main effect of age not statistically significant. dropped to 20% and 30%, respectively, among 9- to 19-year-olds. For definitions based on eating after 11 PM, night eating was somewhat less common: fewer than 7% of 9-year-olds and just over 25% of 19-year-olds exhibited one or two episodes of night eating by this definition. Definitions specifying the amount of food consumed after dinner resulted in even smaller numbers of girls that met night eating criteria. Specifically, 8% and 22% of 9- or 19-yearolds, respectively, reported at least one night eating episode when an intake of 25% of daily calories after dinner was required, and even fewer girls, 3% of 9-year-olds and 4% of 19-year-olds, met the criterion of 50% or greater total daily intake after dinner. For the most inclusive definition (25% after 7 PM), there was a proportional decrease in prevalence when requiring presence of night eating on 2 days vs. 1. At each age level, about twice as many girls reported night eating on 1 day than on 2 days. For all other definitions, night eating on 2 days was by far less common than night eating on 1 day. Across the different age groups and definitions, those meeting criteria on 1 day typically outnumbered those meeting criteria on 2 days by a factor of 10. As predicted, night eating was significantly more common with increasing age, and this age effect was significant for each of the definitions when requiring night eating on 1 day (the main effect of age in GEE models: z, 2.59 to 15.76; p 0.01) except for the definition involving eating 25% of the daily calories after dinner (z 2.14; p 0.03). For the more inclusive definitions of eating 25% and 50% after 7 PM and eating after 11 PM, a significant age effect was found also for night eating on 2 days (z, 6.53 to 11.85; p ). The effects of age were not tested for the definition involving eating 50% of the daily calories after dinner on 2 days because only one girl (a 13-year-old) exhibited 2 days of night eating by this definition. Because very few girls reported eating 25% (3 to 13 girls, depending on age) or 50% (one girl) of their daily calories after dinner on 2 days, these definitions were dropped from further analyses. Estimates based on such small samples are unlikely to be reliable. Characteristics of Recurrent Night Eating: Caloric and Macronutrient Intake during Night Eating To further describe recurrent night eating, food intake data from girls who exhibited the behavior on 2 days were examined. As shown in Table 2, among recurrent night eaters, the mean number (per day) of distinct eating episodes during the night was lowest for the definition involving eating after 11 PM and was quite similar for the definitions involving eating 25% or 50% of total calories after 7 PM. There were no significant age differences in mean number of eating episodes, regardless of definition of night eating. Table 3 shows the average daily calories consumed during night eating, by each of the three remaining definitions. As one would expect, night eaters who consumed 50% of their total daily calories after 7 PM ate the most total calories at night. The smallest amounts of caloric consump- OBESITY RESEARCH Vol. 12 No. 8 August

6 Table 3. Daily mean (SD) of total number and percentage of kilocalories consumed at night on days when night eating occurred, by definition of night eating Definition of recurrent night eating: eating on 2 days 25% of total after 7:00 PM 50% of total after 7:00 PM Any eating after 11:00 PM Total number of at night Percentage of at night Total number of at night* Percentage of at night Total number of at night* Percentage of at night* (336.4) 44.4 (10.2) (360.2) 61.7 (7.6) (134.8) 19.9 (2.7) (417.2) 44.3 (11.6) (462.8) 65.4 (9.5) (393.9) 15.9 (7.5) (403.2) 46.0 (11.1) (493.8) 63.4 (8.3) (386.5) 18.8 (13.0) (461.3) 47.0 (11.2) (680.4) 63.2 (10.2) (486.7) 17.5 (15.3) (378.0) 48.5 (12.4) (486.6) 66.7 (11.9) (219.6) 18.1 (12.4) (360.4) 48.4 (11.9) (356.0) 65.2 (8.8) (110.6) 10.2 (3.4) (399.3) 46.5 (11.8) (352.3) 64.7 (11.9) (485.8) 18.5 (14.1) (410.5) 47.4 (11.6) (443.8) 65.8 (10.5) (384.9) 19.8 (13.9) (441.0) 47.9 (13.5) (610.2) 67.8 (12.1) (441.7) 20.5 (16.2) (358.4) 48.0 (13.0) (374.3) 68.3 (12.3) (283.6) 22.1 (10.8) (428.5) 48.6 (14.2) (484.8) 68.3 (12.3) (386.7) 22.3 (16.4) Only days where night eating occurred were included in the analysis. At study entry, one-half of the girls were 9 or 10 years of age, respectively. * No Significant main effect of age. Main effect of age, p Main effect of age, p tion during night eating were observed when night eating was defined as any eating after 11 PM. Total caloric intake at night increased significantly with age only for the definition based on consumption of 25% of the daily calories after 7 PM (z 3.94; p ). Table 3 also shows caloric consumption during night eating as the percentage of total daily calories. Two of our definitions specified a minimum percentage daily intake (25% and 50% after 7 PM), and, not surprisingly, girls who ate 50% of their calories at night consumed the greatest percentage of their calories at night. Among those who reported eating after 11 PM, typically 20% of their daily intake occurred at night. There were significant age-related increases for the definitions involving consumption of 25% and 50% after 7 PM (z 4.72 and 3.07; p 0.01, respectively). The age differences in percentage daily intake did not reach statistical significance for the definition involving consumption after 11 PM. Macronutrient intake from night eating was examined by coding percentage of calories consumed at night from protein, fats, and carbohydrates. As shown in Table 4, protein intake from night eating was fairly similar across the two definitions involving eating after 7 PM, ranging from 14% to 18%, and was lower when night eating was defined restrictively as any eating after 11 PM. Percentage intake from protein during night eating did not vary significantly with age for the definitions of consuming 50% of total calories after 7 PM or any eating after 11 PM. For the definition involving eating 25% of total calories after 7 PM, caloric intake from protein tended to decrease with age (z 3.31; p 0.001). Percentage caloric intake from fats (Table 5) during night eating was quite high, ranging from 32% to 41% when night eating was defined based on eating 25% or 50% of total calories after 7 PM, and decreased significantly with age (z 9.37 and 5.84, respectively). As shown in Table 6, for the definitions based on eating 25% or 50% of total calories after 7 PM, atall ages, 45% or more of the calories consumed at night were from carbohydrates, although the percentage of calories from carbohydrates increased with age (z 7.34 and 4.14, respectively; p ). Percentage intake from fats during night eating did not vary significantly with age when using the eating after 11 PM definition, and inspection of Table 5 suggests that recurrent night eating after 11 PM involves food that contains less fat than the night eating episodes captured with the two other definitions. For the 1316 OBESITY RESEARCH Vol. 12 No. 8 August 2004

7 Table 4. Mean (SD) of percentage of calories consumed at night from protein, by definition of night eating Definition of recurrent night eating: eating on 2 days 25% of total 50% of total after 7:00 PM Any eating after 11:00 PM (5.6) 14.2 (6.1) 5.0 (2.7) (5.4) 16.0 (6.3) 9.4 (4.1) (5.4) 14.1 (5.6) 8.5 (6.0) (5.9) 15.7 (5.1) 9.9 (6.6) (6.6) 17.8 (7.2) 10.1 (8.5) (6.0) 17.2 (7.4) 8.5 (2.2) (6.0) 14.6 (7.4) 10.0 (12.3) (6.1) 15.4 (6.6) 9.4 (8.7) (6.1) 16.1 (5.9) 9.5 (8.0) (6.0) 13.9 (4.8) 13.1 (16.3) (6.1) 14.3 (5.6) 9.7 (6.4) At study entry, one-half of the girls were 9 or 10 years of age, respectively. * Main effect of age, p Main effect of age not statistically significant. definition involving eating after 11 PM, carbohydrates contributed a uniformly high percentage of calories to intake at night (53.8% to 68.8% for ages 10 to 19; the highest percentage, 83.9% at age 9, should be regarded with caution because the data were from only two girls). Table 5. Mean (SD) of percentage of calories consumed at night from fats, by definition of night eating Definition of recurrent night eating: eating on 2 days 25% of total 50% of total Any eating after 11:00 PM (8.8) 39.5 (8.1) 11.0 (8.3) (9.3) 41.4 (8.6) 35.5 (14.6) (9.1) 39.4 (7.7) 22.6 (11.7) (9.1) 38.2 (9.6) 25.0 (17.7) (10.1) 38.7 (9.7) 28.4 (13.9) (9.1) 37.2 (8.8) 27.6 (3.8) (10.3) 36.0 (12.9) 27.6 (16.8) (10.4) 35.1 (8.1) 21.9 (14.0) (10.5) 36.9 (9.5) 24.3 (16.8) (10.8) 33.2 (9.9) 26.1 (15.1) (10.0) 33.9 (7.4) 26.5 (15.7) At study entry, one-half of the girls were 9 or 10 years of age, respectively. * Main effect of age, p Main effect of age not statistically significant. Demographic Characteristics of Recurrent Night Eating Demographic characteristics were predictive of recurrent night eating. As shown in Table 7, a significantly greater percentage of black girls exhibited night eating for all definitions (z 3.39 to 8.38; p 0.001). Depending on the definition of night eating, black girls were between 6 and 14 times more likely to be night eaters than white girls were. Regarding parental education (Table 8), girls with less educated parents were more likely to exhibit night eating when it was defined as involving consumption of 25% and 50% after 7 PM (z 3.24 and 2.99, respectively; p 0.005). For these two definitions, girls with less educated parents were between 2 and 5 times more likely to be night eaters than girls with more educated parents. To examine the possibility that the ethnic differences in night eating prevalences were at least partly a function of ethnic differences in socioeconomic status, parental education was added to the models examining the relation between ethnicity and night eating. This resulted in only a minimal change in the model estimates for ethnicity. The main effect of ethnicity was still significant for all definitions of night eating (z 3.79 to 7.70; p ), with odds ratios ranging from 5 to 14. Recurrent Night Eating and Childhood Overweight Table 9 shows the number of girls exhibiting recurrent night eating by overweight status. No significant main or interaction effects involving obesity were found for any definition of night eating (z 0.01 to 1.93; p 0.05) in models that were adjusted for the potentially confounding variables of ethnicity and parental education as control variables and included interaction terms of ethnicity-byobesity and education-by-obesity. Hence, recurrent night eating was not found to be significantly associated with obesity, nor did age, ethnicity, or parental education moderate this relationship. Finally, there were no significant differences in total caloric intake between recurrent night eaters and girls who did not report recurrent night eating (data not shown). Discussion Night eating is considered the core behavioral feature in contemporary definitions of NES. To our knowledge, the OBESITY RESEARCH Vol. 12 No. 8 August

8 Table 6. Mean (SD) of percentage of calories consumed at night from carbohydrates, by definition of night eating Definition of recurrent night eating: eating on 2 days 25% of total 50% of total Any eating after 11:00 PM (11.4) 46.3 (13.0) 83.9 (5.6) (11.1) 42.6 (10.7) 55.2 (16.1) (11.3) 46.5 (10.3) 68.8 (13.5) (11.2) 46.1 (10.8) 65.1 (21.9) (12.3) 43.4 (12.2) 61.5 (17.0) (11.2) 45.6 (11.9) 63.9 (5.0) (11.6) 47.3 (14.1) 62.3 (18.0) (12.5) 49.3 (10.3) 68.2 (18.4) (11.9) 46.5 (9.2) 61.7 (18.5) (11.7) 51.5 (10.0) 53.8 (20.9) (11.7) 49.7 (9.5) 62.9 (19.1) At study entry, one-half of the girls were 9 or 10 years of age, respectively. * Main effect of age, p Main effect of age not statistically significant. present study represents the first attempt to study night eating in a community sample of adolescent girls. Proposing operationalized criteria for the four most commonly used definitions and adding our own, simple definition of night eating, we sought to offer basic descriptive information about this behavior. Three major findings are of note. One, our results illustrate that rates of night eating varied widely depending on the restrictiveness of the criteria. Two, significant age effects were found, indicating that, in general, night eating was more common among older girls than among younger girls. Further, for definitions involving eating 25% or 50% of total daily calories after 7 PM, the percentage of total calories and the percentage of calories from carbohydrates consumed during night eating increased with increasing age. Three, recurrent night eating was found to be associated significantly with ethnicity and parental education (this study s proxy for socio-economic status), but not with obesity. Three elements of the definition of night eating were considered in the current report: time of day, percentage of daily calories consumed, and frequency of night eating events. The literature discusses the cultural relativity of time of day regarding the evening meal (10). Our data clearly show that eating after 7 PM, even eating a considerable percentage of daily caloric intake (50%) after 7 PM, is quite common. Not surprisingly, recent studies of NES have moved away from the most inclusive definition (25% kcal after 7 PM), a definition that captured 40% to 50% of the girls at any one time. Defining time of day relatively late in the evening (after 11 PM) resulted in a substantial decrease in the number of girls meeting criteria for night eating, although the percentage of girls in this category is still considerable (from 6.5% in 9-year-olds to 21% in 19-yearolds). When a strict caloric definition was used (50% kcal), the frequency of night eating decreased dramatically. Imposing the additional requirement that the eating occur after dinner reduced prevalence rates by a factor of 10 or greater compared with definitions that were based solely on time of day. Finally, our data also show that when requiring that the behavior occur with some regularity (defined here as two 24-hour periods), in addition to the strict caloric definition, the frequency of night eating was reduced again typically by a factor of 10. Clearly, recurrent night eating involving a high caloric intake after 7 PM or involving eating late in the evening (after 11 PM) is not normative. Instead, the frequency estimates range from 1% to 3% in the younger girls to 3% to 5% in the older girls. We note that when specifying that over 50% of daily caloric intake is consumed after dinner, in the multiple years with data available for such a classification, only one girl in 2000 was found to meet these criteria. Given the profound effect of varying definitions used in the literature on prevalence rates, published results about prevalence of night eating cannot be easily interpreted. The field needs to move toward a commonly accepted definition, or, minimally, studies need to define specifically how night eating was operationalized, to permit comparison of findings across studies. Our results support the hypothesis that night eating becomes increasingly more common as girls get older. Furthermore, the amount or percentage of total calories consumed during night eating tended to increase with increasing age. The macronutrient content of foods consumed during night eating suggests a relatively high intake of calories from carbohydrates and fats and relatively lower intake from protein. Indeed, among girls with recurrent night eating who met the strict time-based definition of eating after 11 PM, on average 60% of calories consumed from night eating were derived from carbohydrates. For all three definitions used in the analysis exploring macronutrient intake in recurrent night eaters, percentage caloric intake from fat also was quite high. The literature, to date, is silent on developmental considerations when defining night eating. Likely, this increase in both frequency and caloric content reflects lifestyle changes, such as girls being permitted to stay up later, having greater autonomy over where or what to eat, and having greater access to food. These findings raise questions as to the clinical significance of 1318 OBESITY RESEARCH Vol. 12 No. 8 August 2004

9 Table 7. Percentage (number) of girls meeting definition of night eating, by definition of night eating and girls ethnicity (white vs. black) Definition of recurrent night eating: eating on 2 days 25% of total 50% of total Any eating after 11:00 PM White Black White Black White Black 9 9.6% (58) 16.5% (72) 1.0% (6) 2.3% (10) 0.0% (0) 0.5% (2) % (98) 22.0% (226) 0.9% (10) 3.0% (31) 0.2% (2) 0.8% (8) % (127) 23.9% (230) 1.6% (15) 3.2% (31) 0.2% (2) 1.6% (15) % (115) 24.1% (230) 1.4% (13) 3.8% (36) 0.5% (5) 1.5% (14) % (97) 25.1% (231) 1.4% (12) 4.6% (42) 0.8% (7) 1.1% (10) % (54) 24.6% (118) 2.0% (8) 4.8% (23) 0.7% (3) 0.4% (2) % (73) 24.1% (95) 2.4% (11) 3.6% (14) 2.0% (9) 2.0% (8) % (134) 25.9% (206) 2.6% (19) 4.2% (33) 1.6% (12) 3.5% (28) % (75) 23.2% (101) 3.0% (11) 4.8% (21) 0.8% (3) 4.6% (20) % (113) 28.9% (119) 2.6% (12) 6.6% (27) 4.5% (21) 4.9% (20) % (99) 27.5% (152) 5.3% (22) 5.4% (30) 4.5% (19) 5.2% (29) At study entry, one-half of the girls were 9 or 10 years of age, respectively. * Main effect of ethnicity, p Main effect of ethnicity not statistically significant. Table 8. Percentage (number) of girls meeting definition of night eating, by definition of night eating and parental education Definition of recurrent night eating: eating on 2 days 25% of total 50% of total Any eating after 11:00 PM <4 years of 4 years of <4 years of 4 years of <4 years of 4 years of % (85) 11.0% (45) 2.2% (14) 0.5% (2) 0.3% (2) 0% (0) % (225) 12.8% (99) 2.2% (29) 1.6% (12) 0.5% (6) 0.5% (4) % (245) 16.0% (112) 2.8% (34) 1.7% (12) 1.1% (13) 0.6% (4) % (232) 16.0% (111) 2.9% (34) 2.2% (15) 1.1% (13) 0.7% (5) % (233) 14.5% (95) 4.1% (45) 1.4% (9) 1.1% (12) 0.8% (5) % (121) 16.7% (51) 4.2% (24) 2.3% (7) 0.5% (3) 0.7% (2) % (107) 17.4% (57) 3.7% (19) 1.5% (5) 1.6% (8) 2.8% (9) % (226) 19.6% (105) 3.4% (33) 3.5% (19) 2.9% (28) 1.9% (10) % (104) 22.6% (67) 4.3% (21) 3.7% (11) 3.3% (16) 2.4% (7) % (141) 26.7% (90) 4.3% (23) 4.5% (15) 4.8% (26) 4.5% (15) % (174) 25.0% (77) 5.2% (34) 5.8% (18) 4.6% (30) 5.5% (17) At study entry, one-half of the girls were 9 or 10 years of age, respectively. * Main effect of parental education, p Main effect of parental education not statistically significant. OBESITY RESEARCH Vol. 12 No. 8 August

10 Table 9. Percentage (number) of girls meeting definition of night eating, by definition of night eating and girls overweight status (overweight vs. not overweight) Definition of recurrent night eating: eating on 2 days 25% of total after 7:00 PM* 50% of total after 7:00 PM Any eating after 11:00 PM Not overweight Overweight Not overweight Overweight Not overweight Overweight % (124) 14.3% (6) 1.6% (16) 0.0% (0) 0.2% (2) 0.0% (0) % (284) 16.0% (39) 1.9% (34) 2.5% (6) 0.5% (10) 0.0% (0) % (306) 25.3% (49) 2.3% (40) 3.1% (6) 0.9% (15) 1.0% (2) % (290) 20.0% (51) 2.6% (42) 2.7% (7) 1.1% (17) 0.0% (0) % (284) 21.6% (44) 2.9% (45) 4.4% (9) 0.9% (14) 1.5% (3) % (147) 19.0% (23) 3.7% (28) 2.5% (3) 0.7% (5) 0.0% (0) % (124) 21.7% (38) 2.9% (19) 2.9% (5) 2.2% (14) 1.1% (2) % (272) 22.8% (52) 3.1% (39) 3.9% (9) 2.9% (36) 0.9% (2) % (139) 26.5% (26) 3.7% (25) 6.1% (6) 2.7% (18) 4.1% (4) % (188) 29.1% (41) 4.0% (29) 6.4% (9) 4.4% (32) 6.4% (9) % (171) 30.2% (80) 5.3% (37) 5.7% (15) 4.6% (32) 5.7% (15) At study entry, one-half of the girls were 9 or 10 years of age, respectively. * Main effect of age, p Main effect of age not statistically significant. these developmental increases in night eating. In regard to obesity, our results do not suggest that night eating, as defined in the present study, is associated with obesity. The literature has produced conflicting results about the relationship between NES (involving the additional symptoms of morning anorexia and, in some studies, mood disturbance) and obesity (3). It is possible that the behavior of night eating by itself does not confer increased risk for the development of obesity in adolescents. We found that recurrent night eating was significantly more common among black girls than among white girls when definitions focused on eating after 7 PM. Recurrent night eating late in the evening (after 11 PM) also was more common in black girls, but the total number of girls reporting late night eating was small, and the ethnic group differences did not reach statistical significance. Socioeconomic status was also correlated significantly and inversely with recurrent night eating. Girls whose parents had less than 4 years of education were more likely to report recurrent night eating (after 7 PM) than girls who had at least one parent with 4 or more years of. It should be noted that the effect of ethnicity remained even when parental education (a proxy for SES) was considered, suggesting that ethnic differences were not a function of income or education level. Future studies need to explore the mediating variables that account for these demographic differences. For example, black families may eat later in the day than white families due to different cultural norms or employment patterns (e.g., working later shifts). We found relatively little variation in the number of episodes of night eating across three definitions, which raises the conceptual issue of whether night eating should, indeed, be characterized as episodic. Unlike binge eating, which is defined by the amount of eating during a discrete period of time and loss of control over the distinct eating episode (13), night eating is defined by time of day and amount of food consumed during that time (1,3). For night eating, the clinically relevant issue would seem to be that an individual consumes a large amount of food that is eaten at a time when most others would not be eating, rather than a focus on the number of episodes that occur during the night. Several additional questions warrant further exploration. For example, future research might explore whether adolescent girls who engage in night eating are more likely to report disordered eating, such as binge eating or restrictive dieting during the day. Also unclear is whether recurrent night eating is associated with more general psychopathology (e.g., depression). Indeed, full syndrome definitions of NES often require presence of mood disturbance (3), and epidemiological studies are needed that examine the relationship between the behavior of night eating and mood disturbances. In other words, although our data highlight the developmental increases in night eating behavior for black and white adolescent girls, we do not yet know whether 1320 OBESITY RESEARCH Vol. 12 No. 8 August 2004

11 such eating is problematic and should be of concern or, instead, is simply a response to normal adolescent changes in schedule and independence (e.g., later bedtimes, more food choice). Examination of caloric intake data showed that these late evening eating episodes varied considerably as reflected in the sizable SDs. Future studies might explore definitions that combine late time of day (11 PM or later) and a minimum caloric amount. Several limitations need to be acknowledged. Our dietary assessment was based on a 3-day food diary, making it impossible to determine frequency of night eating across a longer time period. Studies are needed where night eating is measured across an observation period that is consistent with time frames used for diagnostic purposes (e.g., 3 months). Night eating was based on self-report information regarding the time of the event and, in some definitions, the actual foods consumed. As with any classification scheme, small inconsistencies (e.g., noting in the food record that the eating occurred at 10:55 PM when it occurred at 11:05 PM) can have a major effect (i.e., in the former instance, the event would not have been captured by our definition of eating after 11 PM). These limitations are off-set by several strengths, including quite detailed information as obtained by the 3-day food diaries, the availability of data from a large and diverse community sample, and the delineation of operationalized criteria for night eating. The present study represents only a first (but necessary) step in describing night eating. We propose, based on our data, that the night eating criterion of NES should include, minimally, these three elements: time of day, a caloric amount, and a frequency criterion. More heterogeneous samples that include a broader age range and both patient and community populations need to be studied to further clarify the specific cutpoint for each of these criteria (e.g., the percentage of daily caloric intake, the time of day). The adoption of multicomponent criteria by researchers would allow for cross-study comparisons that could result in refinement of diagnostic criteria for NES and additional study of its clinical correlates with samples that are diverse in gender, ethnicity, and clinical presentation. Acknowledgments This research was supported by NHLBI Grant HL- DK71122 and by the National Institute of Mental Health and the National Institute of Diabetes, Digestive and Kidney Diseases Grants R01-MH and R01-MH This research was also supported by Contracts HC and Cooperative Agreements U01-HL from NHLBI of NIH. Program Office: NHLBI (Eva Obarzanek, Project Office 1992 to present; and Gerald H. Payne, Project Officer 1985 to 1991). References 1. 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