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PAPER
Night eating and weight change in middle-aged men
and women
GS Andersen
1,2,3
, AJ Stunkard
4
, TIA Sørensen
2
, L Petersen
2
and BL Heitmann
1,2
*
1
Research Unit for Dietary Studies, Institute of Preventive Medicine, Copenhagen University Hospital, Copenhagen K,
Denmark;
2
Danish Epidemiology Science Centre, Institute of Preventive Medicine, Copenhagen University Hospital,
Copenhagen K, Denmark;
3
Research Centre for Prevention and Health, Glostrup University Hospital, Philadelphia, USA; and
4
Department of Psychiatry, University of Pennsylvania, Philadelphia, USA
OBJECTIVE: To examine the association between the habit of eating at night, and the 5-y preceding and 6-y subsequent weight
changes in a middle-aged population, with particular focus on the obese.
DESIGN: Prospective study with initial examination of the cohort in 1982–83, re-examination in 1987–88 and a third
examination in 1992–93.
SUBJECTS: The Danish MONICA cohort includes an age- and sex-stratified random sample of the population from the Western
part of the Copenhagen County. Out of 2987 subjects participating in 1987–88, a total of 1050 women and 1061 men had
been examined in 1982–83, and 1993–94 too. Subjects working night shifts were excluded.
MEASUREMENTS: Night eating in 1987–88, 5-y preceding and 6-y subsequent weight change.
RESULTS: In total, 9.0% women and 7.4% men reported ‘getting up at night to eat’. Obese women with night eating
experienced an average 6-y weight gain of 5.2 kg (P ¼ 0.004), whereas only 0.9 kg average weight gain was seen among obese
women who did not get up at night to eat. No significant associations were found among all women, or between night eating
and the 5-y preceding weight change for women. Night eating and weight change were not associated among men.
CONCLUSION: Night eating was not associated with later weight gain, except among already obese women, suggesting that
getting up at night to eat may be a contributor to further weight gain among the obese.
International Journal of Obesity (2004) 28, 1338–1343. doi:10.1038/sj.ijo.0802731
Published online 27 July 2004
Keywords: night eating; night-eating syndrome; weight change; eating disorder; energy regulation
Introduction
Several environmental factors, presumably in interaction with
genetic factors, seem to exert a constant pressure on the
human body to increase energy intake and decrease energy
expenditure, and the sensitivity to these factors may vary
between subgroups of the population.
1,2
One group of
behavioural traits that may generate imbalance in the energy
regulation by increasing energy intake, and hence possibly
relate to obesity and weight gain, are abnormal eating patterns
such as restrained eating, binge eating and night eating.
3–10
The night-eating syndrome was described in 1955 as a
condition characterised by morning anorexia (minimal or no
calorie intake at breakfast), evening hyperphagia (at least 50% of
daily calorie intake after the evening meal) and insomnia, and it
has later been broadened to include night time awakenings with
food intake.
11–14
Several studies have used this definition and
found frequencies of the night-eating syndrome ranging from 8
to 27% among obese patients.
3,13–17
Although the symptom of
night eating is a main component in the night-eating
syndrome, systematic studies of the relation of this symptom
to overweight, independent of the syndrome, are warranted.
18
We therefore hypothesised that night eating, that is,
getting up at night to eat, as reported in the general
population, could be related to later weight gain, and we
investigated whether night eating per se predicts weight gain,
or weight gain predicts night eating.
Methods
Population
In 1982, a total of 4807 Danish citizens born in 1922, 1932,
1942 or 1952 were invited to participate in the Danish
Received 30 June 2003; revised 4 April 2004; accepted 25 April 2004;
published online 27 July 2004
*Correspondence: Dr BL Heitmann, Research Unit for Dietary Studies,
Institute of Preventive Medicine, Kommunehospitalet, DK-1399 Copen-
hagen K, Denmark.
E-mail: BLH@ipm.hosp.dk
International Journal of Obesity (2004) 28, 1338–1343
&
2004 Nature Publishing Group All rights reserved 0307-0565/04
$
30.00
www.nature.com/ijo
MONICA project, which was carried out as part of the
Glostrup Population studies in the greater Copenhagen
County. The MONICA cohort includes an age- and sex-
stratified random sample of the population from the Western
part of the Copenhagen County, selected from the Central
Person Register. In all, 226 subjects of non-Danish origin
were excluded, thereby reducing the sample to 4581
subjects. A total of 3608 (79%) accepted the invitation,
forming the original baseline examination from 1982 to 83
(MONICA 1 (M-82)). This group was invited to a re-
examination 5 y later in 1987–88 (Gen-MONICA (M-87)),
and 2987 (83%) subjects participated. Finally, in 1993–94
(MONICA 10 (M-93)), the cohort was invited to a third
examination, and 2436 (68%) of the initial 3608 individuals
participated in all the three examinations.
The non-participants included 324 subjects who died in
the follow-up period between M-82 and M-93, but char-
acteristics of the non-participants have been described in
detail elsewhere.
19
Out of 2839 subjects who gave answers to
the night-eating question in 1987–88, 518 were excluded
due to non-participation in either M-82 or M-93. Further-
more, 210 night and shift workers were excluded from
further analysis, since night and shift workers may have
misinterpreted the questionnaire and hence reported night
eating despite actually working at night and therefore not
getting up at night to eat.
Anthropometrical data
Height was measured to the nearest 0.5 cm with subjects
standing without shoes, heels together and head in a
horizontal Frankfurter plane. Body weight was measured to
the nearest 0.1 kg using a SECA scale, with subjects wearing
only light clothes.
Follow-up and historical information on weight change
Preceding weight change was calculated by subtracting M-82
measurements of body weight from M-87 measurements of
body weight. Subsequent weight change was calculated by
subtracting M-87 measurements of body weight from M-93
measurements.
Questionnaire
An extensive questionnaire on sociodemographic variables
and lifestyle was filled in at all the three examinations. In M-
87, subjects were specifically asked: ‘Do you get up at night
to eat?’ to signify night eating. A total of 2839 out of the
2987 subjects gave answers to this question. Subjects
recorded their present smoking habits, and were subse-
quently classified as current, former, occasional or never-
smokers. Leisure-time activity was recorded on a four-point
scale ranging from almost completely inactive, some physi-
cal activity, regular activity and regular hard physical
training for competition. Education was recorded as the
number of years in school, and the subjects’ education was
classified as r7, 8–11 and Z12 y. Restrained eating at meals
was recorded by asking: ‘Do you refrain from eating your fill
at meals?’ and subjects classified on a four-point scale
ranging from never, occasionally, often and frequently.
Subjects with a body mass index (BMI) Z30 were classified
as obese.
Statistical analysis
The difference in proportions between night eaters and
others was tested using a w
2
test. Association between night
eating and the preceding weight change was analysed with
multiple logistic regression models, with night eating as the
response variable. Change in body weight from M-82 to
M-87 (kg) was included as the main explanatory continuous
variable. A first series of models included only night eating
and weight change. In a second series of models, age,
smoking habits (recoded as current smokers and others),
physical activity (recoded as inactive, some activity and
regular/hard activity), years in school, restrained eating at
meals and BMI in M-82 were included as explanatory
variables. To examine whether the association between
preceding weight change and night eating differed according
to obesity in M-82, a third series included the product of
night eating and obesity in the equation.
Multiple linear regression was used to estimate the effect of
night eating on subsequent weight change from M-87 to
M-93 as response variable, and night eating was included as
the main explanatory variable. In a first series of crude
models, only the response variable and the main explanatory
variable were included. A second series included the
explanatory variables age, smoking habits, years in school,
leisure time physical activity, restrained eating at meals,
baseline BMI and weight change from M-82 to M-87. To
examine whether the association between night eating and
subsequent weight change differed according to obesity in
M-87, a third series included the product of night eating and
obesity in the equation.
All data were analysed using the SAS 8.02 statistical
software package.
Results
Non-participation
The 518 subjects excluded due to non-participation in M-82
or M-93 were found to differ somewhat from the partici-
pants, in that they included slightly more older people,
and slightly more people with a BMI Z30 when examined
at M-87.
Descriptive analysis
In total, 95/1050 (9.1%) women and 78/1061 (7.4%) men
reported night eating. Table 1 gives the characteristics
among night eaters compared to others on selected variables.
Night eating and weight change
GS Andersen et al
1339
International Journal of Obesity
Among the women, a significantly greater fraction of night
eaters were older than 54 y of age, had r7 y of school, were
daily smokers and unemployed.
Night eating and preceding weight change
Night eating was not associated with weight changes
between M-82 and M-87 in the crude and adjusted analyses.
Obesity in M-82 did not modify the association between
preceding weight change and night eating (Table 2).
Night eating and subsequent weight change
For men, night eating was not associated with subsequent
weight change (M-87 to M-93). For women, obesity was
found to modify the association between night eating and
subsequent weight gain (P ¼ 0.01). Analyses revealed that
obese women with night eating experienced a greater
average 6-y weight gain (4.2 kg, 95% confidence interval
1.3–7.0) than the obese women without night eating
(Table 3). The total average 6-y weight gain for obese
night-eating women was 5.2 kg, whereas obese non-night-
eating women experienced only 0.9 kg average weight gain
(Figure 1).
Discussion
In the present study, we used a simple yes/no question to
assess the lifestyle of getting up at night to eat, and
examined its relation to weight change. Our findings
indicate that, when using this assessment of the night-
eating phenomenon, obesity and night eating had a joint
effect on 6-y weight change for women but not for men,
suggesting that night eating may be a significant contributor
to further weight gain among already obese women, but not
for others.
A newly published study on meal patterns and obesity in
Swedish women confirms that obese women have a meal
pattern that is distinct from normal weight women. They
found that obese women consumed more meals in the
evening and night and more between-meal snacking than
normal weight women.
20
It is possible that a feedback
regulation in the non-obese night eaters avoids excessive
energy intake by means of a lowered energy intake, or a rise
Table 1 Characteristics of night eaters and non-night eaters based on the M-87 examination
a
Men Women
Night eating % (n ¼ 78) Others % (n ¼ 983) P
b
Night eating % (n ¼ 95) Others % (n ¼ 955) P
Obesity (BMI Z30) 14 (11) 11 (109) 0.42 13 (12) 9 (84) 0.21
Age (+55 y) 45 (33) 48 (469) 0.63 63 (60) 45 (426) o0.01
School (r 7 in school) 38 (30) 31 (306) 0.18 51 (48) 32 (301) o0.01
Smoker (daily smoker) 59 (46) 48 (470) 0.06 54 (51) 39 (372) o0.01
Physical activity (inactive) 26 (20) 20 (193) 0.21 26 (25) 27 (254) 0.94
Restrained eating at meals (Zoften) 13 (10) 13 (128) 0.95 20 (19) 21 (202) 0.86
Unemployment 27 (21) 19 (191) 0.11 55 (52) 30 (286) o0.01
Weight change 1987–93 (45 kg) 19 (15) 20 (195) 0.90 24 (23) 23 (220) 0.80
Weight change 1982–87 (45 kg) 19 (15) 15 (148) 0.33 15 (14) 19 (186) 0.26
a
Results are given as differences in proportion of selected variables between night eaters and others. Proportions were compared using w
2
test.
b
w
2
test was used to
estimate all P-values in the present study.
Table 2 Night eating and preceding weight change
a
Odds ratio for night eating
Men Women
Preceding weight
change (M-82–M-87)
OR P OR P
Crude 1.02 (0.97; 1.08) 0.46 0.98 (0.94; 1.02) 0.35
Adjusted
b
1.03 (0.98; 1.09) 0.31 0.99 (0.95; 1.04) 0.72
Weight change
among the obese
b,c
0.94 (0.83; 1.06) 0.32 0.99 (0.90; 1.10) 0.90
a
Odds ratios with 95% confidence intervals for night eating vs no night eating
from the prospective analysis of 5-y preceding weight change. Crude data,
adjusted data and adjusted joint effects of weight change and obesity are
presented.
b
Adjusted for age, smoking, years in school, leisure time physical
activity, restrained eating and baseline BMI (M-82).
c
Obesity is defined as a
BMI430 in the M-82 examination.
Table 3 Night eating and subsequent weight change
a
Subsequent weight change in kg (M-87 to M-93)
Men Women
Night eating Estimate P Estimate P
Crude 0.25 (1.35; 0.85) 0.65 0.21 (0.82; 1.24) 0.69
Adjusted
b
0.15 (1.22; 0.92) 0.78 0.75 (0.27; 1.77) 0.15
Night eating among
the obese
b,c
0.10 (2.99; 2.79) 0.95 4.28 (1.42; 7.15) o0.01
a
Weight change (6-y) and corresponding 95% confidence intervals for night
eaters vs non-night eaters. Crude data, adjusted data and adjusted joint effects
of night eating and obesity are presented.
b
Adjusted for age, smoking, years in
school, leisure time physical activity, restrained eating, baseline BMI (M-87),
preceding weight changes (M-82–M-87) and the product of baseline BMI and
preceding weight changes.
c
Obesity is defined as a BMI430 in the M-87
examination.
Night eating and weight change
GS Andersen et al
1340
International Journal of Obesity
in physical activity the following day, whereas such a
feedback mechanism may not be operative in the obese or
the obesity-prone. Obstructive sleep apnoea may be perpe-
tuating night eating due to frequent awakenings, but since
sleep apnoea is twice as common among men as women it is
a less likely explanation.
The present study did not find differences in weight gain
among women with and without night eating in general.
However, the insignificant tendency to a greater weight gain
among the night-eating women, as presented in Figure 1,
could also be a simple consequence of lack of statistical
power.
21
Hence, a weak association between a relatively
seldom symptom of night eating and subsequent weight
gain among women may be difficult to detect if several
pathways to weight gain supervene. Indeed, when analyses
were focusing on the obesity-susceptible subgroups, associa-
tions became significant.
Additionally, it may be argued that the measurement
of night eating with a simple yes/no question with no
specified time frame may have reduced the sensitivity of the
analyses. However, the fact that we were indeed able to
detect interactions using this simple question suggests that
a more sophisticated instrument, specifying the time frame
for this phenomenon, should be able to discriminate even
better, since a random measurement error likely to be
introduced by the simple question would tend to attenuate
our results.
As regards the reported gender differences, it could be
argued that both eating at night and weight change are
related to childbearing and may potentially have influenced
the findings of differences between men and women, but in
our study the exclusion of fertile women (o45) (n ¼ 302) did
not alter the results (data not shown), making this possibility
less likely. Also, the restrained eating may relate to both
night eating and weight change specifically among women,
and may explain part of the found gender differences.
However, in the present study, restrained eating among
women did not confound the associations between night
eating on subsequent weight change. On the other hand,
sex-specific genetic effects on BMI and weight change have
been reported previously.
1,22,23
Studies of the night-eating
syndrome and related conditions have found these condi-
tions to be associated with psychopathology,
13,24–26
and the
difference in associations between men and women in the
present study may reflect sex-specific differences in the
psychopathology of the obese. It could be that night eating is
promoting weight gain because of a positive imbalance in
the energy regulation caused by excessive energy intake
during night. However, the gender and obesity differences in
the association suggest that night eating is not a uniform
phenomenon, but a condition that operates in combination
with obesity, and only among women. Another interpreta-
tion may be that some other mechanism than night eating
was operating and caused the weight change. If this is the
case, this simple assessment of the phenomenon may serve
as an indicator or an intermediate factor for an underlying
determinant. Finally, energy intake at night is likely to
constitute a lower fraction of daily caloric need for obese
men than for obese women, which would make it easier to
detect an association in women.
The lack of an association between preceding weight gain
and night eating is another finding that needs an explana-
tion. In view of the adverse consequences of night eating,
the women suffering from night eating may tend to cease
night eating when a certain level of weight gain is evident.
Since we do not have information on the night-eating status
from M-92, we are unable to perform a further examination
of this issue. On the other hand, this explanation would be
in congruence with the notion of night eating as a
psychopathological condition,
1
which may introduce irre-
gular eating patterns at certain periods of life, especially
among women.
The nature of the night-eating phenomenon is yet to be
established, but abnormal nocturnal levels of the hormones
leptin and ghrelin may provide a biologic mechanism
involved in night eating. For instance, Birketvedt et al
13
found reduced nocturnal levels of leptin among normal- and
overweight women with the night-eating syndrome com-
pared with controls, and hence indicated that attenuated
nocturnal levels of leptin may promote night eating, by
inhibiting sufficient suppression of appetite. Ghrelin is
believed to operate in the opposite direction of leptin by
stimulation of feeding and wakefulness.
27
Augmented levels
of plasma ghrelin were found both immediately before meals
and also at 0100 h, followed by an acute post-prandial
decline in ghrelin levels.
28–30
English et al
31
reported a lack of
this post-prandial decline specifically among the obese. We
speculate that insufficient post-prandial decrease in plasma
ghrelin levels could promote getting up at night to eat
Figure 1 Weight gain (6-y) for night eaters vs non-night eaters among
obese women and all women, respectively. The adjusted and modified effects
of night eating and non-night eating on 6-y subsequent weight change for
45-y-old non-smoking women with some leisure time physical activity,
without restrained eating at meals, 8–11 y of education, average BMI and
belonging to the middle fifth of the preceding weight change. P-values are
based on w
2
test for differences between night eating and non-night eating.
Night eating and weight change
GS Andersen et al
1341
International Journal of Obesity
especially in the obese. Blundell et al
1
offer an alternative
view, as they argue that particularly obese women may try to
exercise cognitive control over food intake which is largely
under physiological control, and hence this attempted self-
control may lead to disordered eating patterns.
In populations followed over a long time period, there is a
strong tendency for weight gain to be followed by weight
loss and vice versa,
33
and weight gain subsequent to night
eating in the present study could be a result of this tendency.
Also, night eating could be a consequence of previous weight
change and inadequate attempts to control weight gain.
However, analyses of night eating and subsequent weight
gain were adjusted for preceding weight gain, and preceding
weight gain was not related to night eating when analysed
separately. Therefore, it is not likely that weight change prior
to night eating can explain the subsequent weight gain in
the present study.
Possible differences of non-participation and dropout from
follow-up may also bias the findings. However, when
comparing the BMI for those who attended only the baseline
examination with those attending all three examinations,
such a bias was not apparent. Still, those who never turn up
for examination have been found to be more obese than
participants.
32
Such a bias may, however, have led to an
underestimation of BMI, and, hence attenuated, not
strengthened the associations between night eating and
weight change among the obese.
Other variables than those included may confound the
present findings. For instance, binge-eating disorders have
previously been associated both with weight gain and
various definitions of night eating, and inclusion of binge-
eating disorder could influence the findings.
18,34
Future
studies with information on diet and dieting pattern may
provide valuable information in the assessment of the
relation between night eating and weight gain.
In conclusion, this simple lifestyle phenomenon of night
eating defined as ‘getting up at night to eat’ did not seem to
be associated with subsequent weight gain, except in a
subgroup of obese women.
Acknowledgements
This study was supported by grants from The Danish Medical
Research Council (the FREJA programme), The Danish
National Research Foundation, The Augustinus Foundation,
and The Danish Ministry of Health.
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