ORIGINAL ARTICLE
Effects of Emotional Eating and Short Sleep Duration on Weight Gain in Female Employees Tatjana van Strien, PhD and Paul G. Koenders, PhD
Objective: To investigate whether there is an interaction between emotional eating and sleep duration on weight change and whether this effect is stronger in women. Design: One-year follow-up study. Setting: Banking environment. Participants: 553 women and 911 men. Measurements and Results: Selfreported emotional eating and body mass index (BMI) at T1 were measured in 2008, and sleep duration and BMI at follow-up (T2) were measured in 2009. A significant emotional eating–sleep duration interaction on BMI change was found in women, but not in men. Conclusions: The finding that the highest weight gain was found in women who combined short sleep duration with high emotional eating—both of them are markers of (chronic) distress– suggests a possible role of poor psychological health and (chronic) stress in this relationship.
T
here is growing evidence that short sleep duration is associated with weight gain and obesity.1,2 Nevertheless, people with short sleep duration show large interindividual differences in weight gain, and recent results suggest that the association of short sleep duration with weight gain may depend on a tendency toward disinhibition.3 Tendency toward disinhibition refers to overconsumption of food in response to food cues or to emotional cues. In people with a high tendency toward disinhibited eating, the association between short sleep duration and weight gain was stronger than in those with a low tendency toward disinhibited eating. Short-duration sleepers with a high tendency toward disinhibition also reported higher intakes of energy. In the study by Chaput et al,3 tendency toward disinhibition was measured with the disinhibition scale of the Three-Factor Eating Questionnaire (TFEQ4 ). The TFEQ is multifactorial5,6 including three items on emotional eating (eating when feeling anxious or blue), however, all loading on a separate factor. For this study, we were interested to find out whether the moderator effect of disinhibited eating on the relationship between short sleep duration and weight gain would also hold true for solely emotional eating. Emotional eating was earlier found to moderate the association between short sleep duration and elevated food consumption in women.7 Whether this increased food intake in the high emotional eaters with short sleep duration also caused weight gain over time was not investigated. This study is therefore the first to examine the possible moderator effect of emotional eating on the association between short sleep duration and weight gain. As a flip side of the same coin, it is also possible to conceive sleep duration as a moderator variable in a significant emotional eating–sleep duration interaction on weight change (dependent From the Institute for Gender Studies and Behavioural Science Institute (Dr van Strien), Radboud University, Nijmegen; Faculty of Earth and Life Sciences (Dr van Strien), Institute of Health Sciences, VU University Amsterdam; and Beter (Dr Koenders), Occupational Health Services, Amsterdam, the Netherlands. Dr Koenders has disclosed no financial interests related to this research. Dr van Strien received royalties for the Dutch Eating Behaviour Questionnaire, published by Boom test uitgevers. The authors declare no conflicts of interest. Address correspondence to: Paul G. Koenders, PhD, Beter, Hogehilweg 21, 1101 CB Amsterdam, the Netherlands ([email protected]). C 2014 by American College of Occupational and Environmental Copyright Medicine DOI: 10.1097/JOM.0000000000000172
variable). Considering that a moderator variable is the individual difference or contextual variable that strengthens or changes the direction of the relationship between an independent and the dependent variable,8 (p. 852) and that the association between emotional eating and weight gain can be expected to be stronger in people with short than in those with normal sleep duration, the association between emotional eating and weight gain may also depend on short sleep duration. Specifically, an earlier study of our research group on people working in a Dutch banking environment showed a significant main effect of emotional eating on change in body mass index (BMI) after 2 years.9 Considering that emotional eating is usually associated with prospective weight gain only in interaction with negative life events,10 this finding is quite remarkable, and can possibly be explained by the fact that the measurement of emotional eating took place in autumn 2008, coincidently the start of the worldwide credit crisis. Seeing their colleagues from Lehman Brothers being fired may have evoked precisely that sort of vague, unlabeled, and uncontrollable anxiety that may trigger emotional eating in the Dutch bankers.11,12 The study did not contain a measure of perceived stress, so the above hypotheses cannot be directly tested. The study did, however, contain a measure for sleep duration, which can be considered an indirect measure of perceived stress because short sleep duration was earlier found to be associated with psychological stress,13 with short sleep duration being a marker of psychological stress.14 This opens the possibility to examine the possible moderator effect of sleep duration on the association between emotional eating and weight gain in this earlier sample. Of further interest for this study is the examination of the possibility that the two-way emotional eating–sleep duration interaction on weight change is moderated by sex. Both emotional eating and sleep disturbances are more prevalent in women than in men.15,16 It can therefore be expected that the two-way emotional eating–sleep duration interaction on weight change is stronger in women than in men. Aim of this study was to assess the possible three-way interaction of sex–emotional eating–sleep duration on 1-year change in body mass (the dependent variable) in a sample of people working in a Dutch banking environment. As already stated, emotional eating was assessed in autumn 2008. Sleep duration was assessed in 2009 and tested against BMI in 2009 (T2) controlled for BMI in the year before (2008) (T1). We hypothesized that the two-way interaction of emotional eating with short sleep duration on weight gain would be stronger in women than in men. In case of a moderator effect of sex, we will proceed with analyses in one sex only. We first tested the hypothesis that emotional eating would act as a moderator variable in that the relationship between sleep duration and increases in BMI would be stronger in participants with high than in those with low degrees of emotional eating. We next tested the hypothesis that sleep duration would act as a moderator variable in that the relationship between emotional eating and increases in BMI would be stronger in participants with short than in those with normal sleep duration. Possible mechanisms underlying a two-way emotional eating–sleep duration interaction on change in BMI will be explored by conducting mediated moderation analyses, that is an analysis on the process through which the overall moderated effect is produced.8 (p. 853) The mediating variable in these analyses is the intake of fatty/sweet food. Earlier, it was found that
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stressed emotional eaters overate on sweet and fatty food15,17,18 and that short sleep duration was associated with higher consumption of energy19 and calories from snacks20 (see Chaput and Tremblay21 for review). We first tested whether the intake of fatty/sweet food mediated the moderator effect of emotional eating on the association of short sleep duration with weight gain. We next tested whether the intake of fatty/sweet food mediated the moderator effect of sleep duration on the association of emotional eating with weight gain.
Intake of Fatty/Sweet Food In addition, in 2009 with a scale consisting of three items, we measured the intake of fatty/sweet food. The items pertained to the intake of (1) cake, (2) candy bars, and (3) chocolate; for example, “What is the number of intakes of sweet pastry, cake, or gingerbread per day?” Response categories ranged from never or less than one to seven.
Possible Confounders MATERIALS AND METHODS Participants
In addition, in 2008 we also asked questions about healthrelated lifestyle because they may act as possible confounders on our model, in that they may obscure the effects of a variable or the relationship between variables. Specifically, in single items we measured the following:
All participants in this study work at a large banking corporation in the Netherlands. Once a year the company issues a webbased lifestyle questionnaire. On the basis of their answers to the lifestyle questions, employees are offered individual feedback and lifestyle improvement advice. For the study, 8066 employees were invited to fill out the questionnaire. The present analyses are based on participants with complete information on all relevant variables in 2007, 2008, and 2009. An additional inclusion criterion was being a non-long-duration sleeper (20 cigarettes per day), (2) moderate smoking ( 0.10). There was, however, a significant positive main effect for dietary restraint on BMI change (B = 0.138 [SE = 0.061]; B`eta = 0.029; P = 0.024; more dietary restraint being associated with increases in BMI). Similarly, no significant three-way interactions were obtained for external eating: the three-way sex–external eating–sleep duration interaction on 1-year change in BMI in the initial model (no confounders) was not significant (R2 change = 0.000; F(1,1455) = 0.708; P = 0.400), and this remained so for the other models (P’s > 0.10). This time there was no significant main effect for external eating on BMI change (B = 0.112 [SE = 0.086]; B`eta = 0.016; P = 0.193 [ns]).
Emotional Eating–Sleep Duration Interaction in the Women Further Explored As recommended by Holmbeck,35 post hoc analyses on model 2 (controlling for the confounders) were conducted to determine the nature of this significant two-way emotional eating–sleep duration
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TABLE 1. Pearson Correlations of the Model Variables Split by Sex (Women: Lower Half; Men: Upper Half) 1 1. BMI change 2. Sleep duration 3. Emotional eating 4. External eating 5. Restrained eating 6. Fatty/sweet food 7. Smoking 8. Sports 9. Physical activity 10. Age 11. Education 12. General healtha
− 0.10* 0.07 0.06 0.06 − 0.06 0.01 − 0.01 − 0.03 0.08 − 0.13* 0.06
2
3
− 0.06
0.02 − 0.06
0.04 − 0.03 0.03 0.04 − 0.10* 0.04 0.01 − 0.12* − 0.01 − 0.03
0.52* 0.23* 0.15* − 0.08 − 0.05 − 0.04 − 0.13* 0.01 0.20*
4 0.00 0.02 0.55* 0.04 0.19* − 0.02 − 0.07 − 0.13* − 0.20* 0.06 0.20*
5
6
7
8
9
10
11
12
0.03 − 0.03 0.19* 0.09*
0.05 0.00 0.20* 0.26* − 0.09
− 0.04 − 0.01 − 0.10* 0.02 − 0.08* − 0.05
− 0.01 0.03 − 0.09* − 0.07 0.05 − 0.07 − 0.07
− 0.03 0.01 − 0.08 − 0.11* 0.03 − 0.03 0.00 0.26*
0.05 − 0.14* − 0.06 − 0.16* 0.09* −007 − 0.02 − 0.09* 0.13*
0.00 0.11* − 0.02 − 0.01 0.12* − 0.03 − 0.06 − 0.10* − 0.03 − 0.01
0.05 − 0.01 0.18* 0.12* 0.03 0.09* 0.03 −0.26* − 0.16* 0.05 − 0.01
− 0.11* − 0.05 0.13* 0.02 0.06 0.10* 0.03
− 0.08 − 0.09 0.03 − 0.11* 0.02 0.01
− 0.12* − 0.01 0.06 − 0.17* 0.10*
0.31* 0.04 − 0.02 − 0.27*
0.09 0.00 − 0.20*
− 0.35* 0.03
− 0.07
*P < 0.01. a A high score means poor general health. BMI, body mass index.
TABLE 2. Sex–Emotional Eating–Sleep Duration Interactions on BMI in 2009 Controlling for BMI in 2008 (BMI Change), Controlling for (1) No Confounders, (2) Age, Level of Education, Smoking, Physical Activity, and Doing Sports, (3) These Confounders Plus the Other Eating Styles, (4) These Confounders Plus (Poor) General Health, and (5) the Full Model (Unstandardized Bs) Steps
(1) No Confounders
(2) Confounders
(3)+ Eating Styles
(4) + General Health
(5) Full Model
3.644* 0.857*
3.709* 0.849* 0.014** − 0.084 0.045 − 0.112 − 0.122
3.242* 0.842* 0.016*** − 0.090 0.042 − 0.106 − 0.115 0.130 0.086
3.328* 0.842* 0.015*** − 0.072 0.082 − 0.094 − 0.135
0.162**
2.931* 0.836* 0.016*** − 0.079 0.076 − 0.091 − 0.128 0.111 0.086 0.154**
1 Intercept BMI 2008 Age Educationa Doing sports Physical activity Smoking External eating Restrained eating General healthb 2 Emotional eating 2008 Sleep duration Sexc
0.126** − 0.002*** 0.257***
0.137** − 0.002*** 0.259***
0.085 − 0.002*** 0.301***
0.117 − 0.002*** 0.251**
0.295 − 0.002*** 0.295***
Interactiond Interactione Interactionf
− 0.001 − 0.184 0.001
− 0.001 − 0.200 0.001
− 0.001 − 0.205 0.001
− 0.001 − 0.202 0.001
− 0.001 − 0.206 0.001
3
4 Interactiong
0.004**
0.004**
0.003**
0.003**
0.003**
*P < 0.0001; **P < 0.05; ***P < 0.01. a Lower education (primary school, lower vocational education, or lower general secondary education) = 1; medium education (intermediate vocational education, higher general secondary education, or pre-university education) = 2; higher education (higher vocational education or academic training) 3. b A high score means a poor general health. c 1= women; 2 = men. d Interaction between emotional eating and sleep duration. e Interaction between emotional eating and sex. f Interaction between sleep duration and sex. g Interaction between emotional eating, sleep duration, and sex. BMI, body mass index.
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Emotional Eating and Sleep Duration on Weight Gain in Female Employees
interaction on weight change in women. We first report the results with emotional eating as a possible moderator variable. The results of the regression for high emotional eating indicated that the degree of sleep duration was significantly and negatively associated with weight gain (B = −0.005; P < 0.001). In contrast, results of the regression for low emotional eating indicated that sleep duration was not significantly associated with weight gain (B = 0.000; P = 0.747). In a similar manner, we also assessed the results with sleep duration as a possible moderator variable. The results of the regression for high sleep duration indicated that the degree of emotional eating was not significantly associated with weight gain (B = −0.033; P = 0.823). In contrast, results of the regression for low sleep duration indicated that emotional eating was significantly and positively associated with weight gain (B = 0.528; P < 0.001).
Mediated Moderation We next conducted a mediated moderation analysis according to the three equations proposed by Muller et al.8 (p. 856 and p. 858) Specifically, in an analysis with emotional eating as a moderator variable (see Table 3), in Equations 1 and 2, variable X (short sleep duration; slope parameter: b11), the moderator MO (emotional eating: b12), and the XMO (short sleep duration–emotional eating interaction: b13) are regressed on the outcome variable (BMI change) and then the mediator ME (intake of fatty/sweet food; slope parameters of X, MO, and XMO, respectively: b21, b22, and b23). In Equation 3, X (b31), MO (b32), XMO (b33), ME (b34), and MEMO (b35) are regressed on the outcome variable (BMI change). According to Muller et al, 8, (p. 856) “to demonstrate mediated moderation, in [equation] 1, [b13] would be expected to be significant (the overall moderator effect on BMI change). In [equation] 2 and 3, either one or both of two patterns should exist: one of the two [b23 and b34] are significant or both [b21 and b35] are significant. And, as a result, the moderation of the residual [XMO] effect, [b33] should be reduced in magnitude (and may be nonsignificant in case of what might be called ‘full’ mediated moderation) compared to the moderation of the overall treatment effect” (in brackets: adaptations to the present equations by TvS). We first tested a mediated moderation model with emotional eating as a possible moderator variable. Specifically, we tested whether the food intake variable fatty/sweet food mediated the moderator effect of emotional eating on the association of short sleep duration with increases in BMI in the women. For these analyses we used model 2 (controlling for the possible confounders). Table 3 presents the regression models that estimate Equations 1 through 3 with these variables. In correspondence with the tables in Muller et al,8 presented here are the unstandardized coefficients (B) and their associated t statistics. As already indicated, in Equation 1, b13 was significant (B = −0.003 [SE = 0.001]; P = 0.005) (R2 change = 0.003; F(1,541) = 7.916; P = 0.005). The moderator effect was not mediated by the intake of fatty/sweet food, as b23 was not significant (P > 0.10), and b34 was only borderline significant (P = 0.064). Also, both b21 and b35 were not significant and the moderation of the residual (XMO) effect (b33) was not reduced in magnitude. (The R2 change of the XMO—emotional eating remains 0.003 (F(1,541) = 8.376; P = 0.004)—when ME and MEMO—the intake of fatty/sweet food and the intake of fatty/sweet food–emotional eating interaction—are partialled out first.) We next tested a mediated moderation model with sleep duration as a possible moderator variable. Specifically, we tested whether the food intake variable fatty/sweet food mediated the moderator effect of sleep duration on the association of emotional eating with increases in BMI in the women. Again we used model 2 (controlling for the possible confounders). Table 4 presents the regression models that estimate Equations 1 through 3 with these variables. As already indicated, in model 2, b13 was significant (B = −0.003 [SE = 0.001]; P = 0.005). The moderator effect of sleep duration on the association of emotional eating with BMI change was partly mediated by the
intake of fatty/sweet food. Both b23 and b34 were not significant (P’s > 0.10). Nevertheless, b21 was significant (B = 0.147 [SE = 0.049]; P = 0.003) and also b35 was significant (B = −0.002 [SE = 0.001]; P = 0.037). In addition, the moderation of the residual (XMO) effect (b33) was, though still significant, also somewhat reduced in magnitude. (The R2 change of the XMO—emotional eating–sleep duration interaction—was reduced from 0.003 (F(1,543) = 7.916; P = 0.005) to 0.002 (F(1,541) = 4.396; P = .035) when ME and MEMO—the intake of fatty/sweet food and the intake of fatty/sweet food–sleep duration interaction—are partialled out first.)
DISCUSSION In this study, we tested the hypothesis that the two-way emotional eating–sleep duration interaction on BMI change would be stronger in women than in men. We also tested the hypothesis that the relationship between short sleep duration and increases in BMI would depend on emotional eating. We also tested the hypothesis that the relationship between emotional eating and increases in BMI would depend on short sleep duration. Al three hypotheses were supported. The two-way emotional eating–sleep duration interaction on BMI change was present only in women but not in men. Women with higher degrees of emotional eating showed a positive and significant association between short sleep duration and increases in BMI, whereas no such association was found in women with lower degrees of emotional eating. Furthermore, women with shorter sleep duration showed a positive and significant association between emotional eating and increases in BMI, whereas no such association was found in women with a more normal sleep duration. The three-way sex–emotional eating–sleep duration interaction on change in body weight was robust for the influences of possible confounders (age, level of education, physical activity, doing sports, smoking, external eating, restrained eating, and poor general health). It also was specific for emotional eating. So, the earlier significant effect of disinhibited eating behavior on the association between short sleep duration and change in BMI in the study of Chaput et al3 was replicated in this study for emotional eating in women. The present finding in women that the association of short sleep duration with increased BMI was dependent on emotional eating (and not on restrained eating or on external eating) would suggest that poor psychological health and inadequate emotion regulation may be a possible underlying factor in this relationship. Emotional eating was earlier found to be associated with inadequate coping styles,36 depressive feelings,37 worries,38 anxiety,39 and sleep-onset latency.43 This is supported by the present finding in women that the association of emotional eating with increased BMI was dependent on short sleep duration—in itself a possible marker of psychological distress.14 At this point it should be noted that the normal and dominant response to distress is eating less because distress is normally associated with physiological reactions that are designed to prepare the individual for a fight-or-flight, response thereby suppressing hunger.40–42 By eating the same or more during distress15,17,18 emotional eaters show an abnormal or atypical stress response. Accordingly, for weight gain to occur, both short sleep duration and high emotional eating seem required, as was also supported by the present results. A further finding in the study by Chaput et al3 was that disinhibited eating also moderated the association between short sleep duration and intake of energy: only short duration sleepers with a high tendency toward disinhibition showed higher intakes of energy, whereas no association between short sleep duration and energy intake was found in people with low tendencies toward disinhibition. In this study, the intake of energy was not measured directly, so we do not know whether the moderator effect of emotional eating on the short sleep duration increase in BMI association can be attributed to a higher food intake of high emotional eaters. Nevertheless, we
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TABLE 3. Mediated Moderation With Emotional Eating as Moderator Variablea Equation 1 Criterion: BMI Change
X sleep MO emo XMO sleepemo ME fatty/sweet food MEMO fatty/sweet food emo
Equation 2 Criterion: Fatty/Sweet Food
Equation 3 Criterion: BMI Change
B
t
B
t
B
t
−0.002 (b11) 0.248 (b12) −0.003 (b13)
−2.300* 2.381* −2.813**
0.000 (b21) 0.147 (b22) 0.001 (b23)
0.354 2.989** 0.906
−0.002 (b31) 0.267 (b32) −0.004 (b33) −0.166 (b34) 0.119 (b35)
−2.269* 2.546* −2.894** −1.855 (P = 0.064) 1.144
a
Effects of the confounders not shown. *P < 0.05; **P < 0.01. BMI, body mass index; emo, emotional eating; fatty/sweet food, intake of fatty/sweet food; fatty/sweet food mo, intake of fatty/sweet food × emotional eating; ME, mediator variable; MO, moderator variable; sleep, sleep duration; sleepemo, sleep duration × emotional eating.
TABLE 4. Mediated Moderation With Sleep Duration as Moderator Variablea Equation 1 Criterion: BMI Change
X emo MO sleep XMO emosleep ME fatty/sweet food MEMO fatty/sweet food sleep
Equation 2 Criterion: Fatty/Sweet Food (Cake)
Equation 3 Criterion: BMI Change
B
t
B
t
B
t
0.248 (b11) −0.002 (b12) −0.003 (b13)
2.381* −2.300* −2.813**
0.147 (b21) 0.000 (b22) 0.001 (b23)
2.989** 0.354 0.906
0.274 (b31) −0.002 (b32) −0.003 (b33) −0.123 (b34) −0.002 (b35)
2.616** −2.399* −2.097* −1.414 −2.090*
a Effects of the confounders not shown. *P < 0.05; **P < 0.01. BMI, body mass index; emo, emotional eating; fatty/sweet food, intake of fatty/sweet food; fatty/sweet food sleep, intake of fatty/sweet food × sleep duration; ME, mediator variable; MO, moderator variable; sleep, sleep duration; emosleep, emotional eating × sleep duration.
did measure the intake of fatty/sweet food (the number of intakes of (1) sweet pastry, cake, or gingerbread, (2) candy bars, and (3) pieces of chocolate per day). Although we found no significant emotional eating–sleep duration interaction effect for the intake of fatty/sweet food, we did find a significant main effect of emotional eating on the intake of fatty/sweet food. Furthermore, although the moderator effect of emotional eating on the association of sleep duration with BMI change did not seem to be mediated by the intake of fatty/sweet food, there was some support found that the moderator effect of sleep duration on the association of emotional eating with BMI change was partly mediated by the intake of fatty/sweet food. The possibility that the intake of fatty/sweet food is (partly) intervening/mediating the mechanism that produces the moderator effect of sleep duration on the association of emotional eating with BMI change is in line with earlier findings. It may be explained by an increased appetite for food as a possible outcome of an enhanced activation of the anterior cingulated cortex (ACC), associated with both short sleep duration and high emotional eating. In an fMRI study, acute sleep deprivation was found to be associated with an increased activation in the right ACC in response to food images.43 The ACC was earlier shown to play an important role in the reward value of various foods.44 A different fMRI study showed that high emotional eaters also showed higher activation of the ACC in response to the reception of a milkshake during a negative mood compared with emotional eaters in a neutral mood.45 Similarly, a disregulated hypothalamic pituitary adrenal axis by stress may also be a possible underlying factor of the increased intake of fatty/sweet food of the high emotional eaters. High emotional eaters with a blunted cortisol 664
stress response have earlier been found to eat more food after distress than those with an elevated stress response.46 Women with high chronic stress and low cortisol stress reactivity also ate significantly more calories from chocolate cake47 and had higher scores on emotional eating in addition to a greater abdominal fatty distribution.48 Poor sleep quality (and not short sleep duration) was found to be associated with reduced cortisol stress reactivity in healthy women,49 and in children and adolescents.50 Although sleep quality and sleep quantity may be entirely unrelated, further research in this respect is needed.
STRENGTHS AND LIMITATIONS A limitation of this study concerns the use of self-reports. Employees may have underestimated their body weight and overestimated their body length. Nevertheless, we controlled BMI in 2009 for BMI in 2008, so the problem of under- or overestimation of BMI as an outcome variable may have been partly ruled out. Moreover, self-reports of variables such as sleep duration and intake of cakes may have been subject to socially desirable responding (systematic under- or overreporting). Social desirability concerns are however not limited to studies that rely on self-report measures. Concerns about the impression that one is conveying may also affect behavior in a direct test of food intake.51 A further limitation is that in this study sleep duration and BMI at T2 were measured at the same time (2009), so it was not possible to prospectively measure effects of short sleep duration on BMI changes. Another limitation is that this study did not contain a direct measure of perceived stress, only an indirect measure (sleep
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Emotional Eating and Sleep Duration on Weight Gain in Female Employees
duration). Also, present findings are limited to the population of office workers and it is not certain that the conclusions are also applicable to the so-called blue-collar workers. A strength of the study is that, in contrast to sleep duration, BMI was prospectively measured in relation to emotional eating. A further strength is that the measurement of emotional eating took place in autumn 2008, coincidently the start of the worldwide credit crisis, which may have evoked in the employees of this bank precisely that sort of vague, unlabeled, and uncontrollable anxiety that may trigger emotional eating.11,12 The homogeneity of this sedentary population can also be regarded as a strength because it rules out individual differences in physical activity during work according to the findings.
CONCLUSIONS Only women, not men, showed a two-way emotional eating– sleep duration interaction on BMI change. Women with higher degrees of emotional eating showed a positive and significant association between short sleep duration and increases in BMI, whereas no such association was found in women with lower degrees of emotional eating. Similarly, women with shorter sleep duration showed a positive and significant association between emotional eating and increases in BMI, whereas no such association was found in women with a more normal sleep duration. The finding that the highest weight gain was found in women who combine short sleep duration with high emotional eating—both of them are a marker of (chronic) distress—would suggest that the problem of weight gain in women with short sleep duration may not be solved by simply telling them to sleep more hours.
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16. Krishnan V, Collop NA. Gender differences in sleep disorder. Curr Opin Pulm Med. 2006;12:383–389. 17. Oliver G, Wardle J, Gibson EL. Stress and food choice: a laboratory study. Psychosom Med. 2000;62:853–865. 18. Van Strien T, Cebolla A, Etchemendy E, et al. Emotional eating and food intake after sadness and joy. Appetite. 2013;66:20–25. 19. Galli G, Piaggi P, Mattingli MS, et al. Inverse relationship of food and alcohol intake to sleep measures in obesity. Nutr Diabetes. 2012;3:e58. 20. Nedeltchva AV, Kilkus JM, Imperial J, Kasza K, Schoeller DA, Penev PD. Sleep curtailemnt is accompanied by increased intake of calories from snacks. Am J Clin Nutr. 2009;89:126–133. 21. Chaput JP, Premblay A. Insufficient sleep as a contributor to weight gain. An update. Curr Obes Rep. 2011;1:245–246. 22. Van Strien T. Nederlandse Vragenlijst voor Eetgedrag. Herziene Handleiding 2013. [Dutch eating Behaviour Questionnaire. Updated manual] 2013. Amsterdam: Boom Test Publishers. 23. Van Strien T, Frijters JER, Bergers GPA, Defares PB. The Dutch Eating Behaviour Questionnaire (DEBQ) for assessment of restrained, emotional and external eating behaviour. Int J Eat Disord. 1986;5:295–315. 24. Van Strien T, Herman CP, Engels RCME, Larsen J, Van Leeuwe JF. Construct validation of the Restraint Scale in normal-weight and overweight females. Appetite. 2007;49:109–121. 25. Van Strien T, Herman CP, Anschutz DJ. The predictive validity of the DEBQexternal eating scale for eating in response to food commercials while watching television. Int J Eat Disord. 2012;45:257–262. 26. Van Strien T, Van de Laar F. Intake of energy is best predicted by overeating tendency and consumption of fat is best predicted by dietary restraint. A fouryear follow up of patients with newly diagnosed type-2 diabetes. Appetite. 2008;50:544–547. 27. Van Strien T, Herman CP, Anschutz D, Engels RCME, de Weerth C. Moderation of distress-induced eating by emotional eating scores. Appetite. 2012;58:277–284. 28. Haskell WL, Lee I-M, Pate RR, Powell KE, et al. Updated recommendation for adults from the American College of Sports Medicine and the American Heart Association. Circulation. 2007;116:1081–1093. 29. Pollock ML, Gaesser GA, Butcher JD, et al. American College of Sports Medicine Position Stand: the recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness in healthy adults. Med Sci Sports Exerc. 1990;22:265–274. 30. Aaronson NK, Muller PD, Cohen ML, et al. Translation, validation and norming of the Dutch language version of the SF-36 Health Survey in community and chronic disease populations. J Clin Epid. 1998;51:1055–1058. 31. Ware JE, Sherbourne CD. The MOS 36 item short form health survey (SF-36). I. Conceptual framework and item selection. Med Care. 1992;30: 473–483. 32. Ouwens MA, Van Strien T, Van Leeuwe JFJ, Van der Staak CPF. The dual pathway model of overeating: replication and extension with actual food consumption. Appetite. 2009;52:234–237. 33. Van Strien T, Koenders PG. How do life style factors relate to general health and overweight. Appetite. 2012;58:265–270. 34. Aiken LS, West SG. Multiple Regression: Testing and Interpreting Interactions. Thousand Oaks, CA: Sage Publications, Inc; 1991. 35. Holmbeck GN. Post-hoc probing of significant moderational and meditational effects in studies of pediatric populations. J Pediatric Psychol. 2002;27:87– 96. 36. Spoor STP, Bekker MJ, Van Strien T, Van Heck GL. Relations between negative affect, coping and emotional eating. Appetite. 2007;48:368–376. 37. Ouwens MA, Van Strien T, Van Leeuwe JFJ. Possible pathways between depression, emotional and external eating: a structural equation model. Appetite. 2009;53:245–248. 38. Belcher BR, Nguyen-Rodriguez ST, McClain AD, Hsu W, Unger JB, SpruijtMetz D. The influence of worries on emotional eating, weight concerns, and body mass index in Latina females youth. J Adolesc Health. 2011;48: 487–492. 39. Nguyen-Rodriguez ST, McClain AD, Spruijt-Metz D. Anxiety mediates the relationship between sleep onset latency and emotional eating in minority children. Eat Beh. 2010;11:297–300. 40. Gold PW, Chrousos GP. Organization of the stress system and its dysregulation in melancholic and atypical depression: high vs low CRH/NE states. Mol Psychiat. 2002;7:254–275. 41. Greeno CG, Wing RR. Stress-induced eating. Psychol Bull. 1994;115:444– 464. 42. Stone AA, Brownell KD. The stress eating paradox. Multiple measurements in adult males and females. Psychol Health. 1994;8:425–436.
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43. Benedikt C, Brooks SJ, O’Daley OG, et al. Acute sleep deprivation enhances the brain’s response to hedonic food stimuli: an fMRI study. J Clin Endocrinol Metab. 2012;97:E443–E447. 44. Grabenhorst T, Rolls ET, Parris BA, d’Souza AA. How the brain represents the reward value of fat in the mouth. Cereb Cortex. 2010;20:1082–1091. 45. Bohon C, Stice E, Spoor S. Female emotional eaters show abnormalities in consumatory and anticipatory food reward: a functional magnetic resonance imaging study. Int J Eat Disord. 2009;42:210–221. 46. Van Strien T, Roelofs K, de Weerth C. Cortisol reactivity and distress-induced emotional eating. Psychoneuroendocrinology. 2013;38: 677–684. 47. Tyron MS, DeCant R, Laugero RD. Having your cake and eating it too: a habit of comfort food may link chronic social stress exposure and
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Effects of Emotional Eating and Short Sleep Duration on Weight Gain in Female Employees Tatjana van Strien, PhD and Paul G. Koenders, PhD
Objective: To investigate whether there is an interaction between emotional eating and sleep duration on weight change and whether this effect is stronger in women. Design: One-year follow-up study. Setting: Banking environment. Participants: 553 women and 911 men. Measurements and Results: Selfreported emotional eating and body mass index (BMI) at T1 were measured in 2008, and sleep duration and BMI at follow-up (T2) were measured in 2009. A significant emotional eating–sleep duration interaction on BMI change was found in women, but not in men. Conclusions: The finding that the highest weight gain was found in women who combined short sleep duration with high emotional eating—both of them are markers of (chronic) distress– suggests a possible role of poor psychological health and (chronic) stress in this relationship.
T
here is growing evidence that short sleep duration is associated with weight gain and obesity.1,2 Nevertheless, people with short sleep duration show large interindividual differences in weight gain, and recent results suggest that the association of short sleep duration with weight gain may depend on a tendency toward disinhibition.3 Tendency toward disinhibition refers to overconsumption of food in response to food cues or to emotional cues. In people with a high tendency toward disinhibited eating, the association between short sleep duration and weight gain was stronger than in those with a low tendency toward disinhibited eating. Short-duration sleepers with a high tendency toward disinhibition also reported higher intakes of energy. In the study by Chaput et al,3 tendency toward disinhibition was measured with the disinhibition scale of the Three-Factor Eating Questionnaire (TFEQ4 ). The TFEQ is multifactorial5,6 including three items on emotional eating (eating when feeling anxious or blue), however, all loading on a separate factor. For this study, we were interested to find out whether the moderator effect of disinhibited eating on the relationship between short sleep duration and weight gain would also hold true for solely emotional eating. Emotional eating was earlier found to moderate the association between short sleep duration and elevated food consumption in women.7 Whether this increased food intake in the high emotional eaters with short sleep duration also caused weight gain over time was not investigated. This study is therefore the first to examine the possible moderator effect of emotional eating on the association between short sleep duration and weight gain. As a flip side of the same coin, it is also possible to conceive sleep duration as a moderator variable in a significant emotional eating–sleep duration interaction on weight change (dependent From the Institute for Gender Studies and Behavioural Science Institute (Dr van Strien), Radboud University, Nijmegen; Faculty of Earth and Life Sciences (Dr van Strien), Institute of Health Sciences, VU University Amsterdam; and Beter (Dr Koenders), Occupational Health Services, Amsterdam, the Netherlands. Dr Koenders has disclosed no financial interests related to this research. Dr van Strien received royalties for the Dutch Eating Behaviour Questionnaire, published by Boom test uitgevers. The authors declare no conflicts of interest. Address correspondence to: Paul G. Koenders, PhD, Beter, Hogehilweg 21, 1101 CB Amsterdam, the Netherlands ([email protected]). C 2014 by American College of Occupational and Environmental Copyright Medicine DOI: 10.1097/JOM.0000000000000172
variable). Considering that a moderator variable is the individual difference or contextual variable that strengthens or changes the direction of the relationship between an independent and the dependent variable,8 (p. 852) and that the association between emotional eating and weight gain can be expected to be stronger in people with short than in those with normal sleep duration, the association between emotional eating and weight gain may also depend on short sleep duration. Specifically, an earlier study of our research group on people working in a Dutch banking environment showed a significant main effect of emotional eating on change in body mass index (BMI) after 2 years.9 Considering that emotional eating is usually associated with prospective weight gain only in interaction with negative life events,10 this finding is quite remarkable, and can possibly be explained by the fact that the measurement of emotional eating took place in autumn 2008, coincidently the start of the worldwide credit crisis. Seeing their colleagues from Lehman Brothers being fired may have evoked precisely that sort of vague, unlabeled, and uncontrollable anxiety that may trigger emotional eating in the Dutch bankers.11,12 The study did not contain a measure of perceived stress, so the above hypotheses cannot be directly tested. The study did, however, contain a measure for sleep duration, which can be considered an indirect measure of perceived stress because short sleep duration was earlier found to be associated with psychological stress,13 with short sleep duration being a marker of psychological stress.14 This opens the possibility to examine the possible moderator effect of sleep duration on the association between emotional eating and weight gain in this earlier sample. Of further interest for this study is the examination of the possibility that the two-way emotional eating–sleep duration interaction on weight change is moderated by sex. Both emotional eating and sleep disturbances are more prevalent in women than in men.15,16 It can therefore be expected that the two-way emotional eating–sleep duration interaction on weight change is stronger in women than in men. Aim of this study was to assess the possible three-way interaction of sex–emotional eating–sleep duration on 1-year change in body mass (the dependent variable) in a sample of people working in a Dutch banking environment. As already stated, emotional eating was assessed in autumn 2008. Sleep duration was assessed in 2009 and tested against BMI in 2009 (T2) controlled for BMI in the year before (2008) (T1). We hypothesized that the two-way interaction of emotional eating with short sleep duration on weight gain would be stronger in women than in men. In case of a moderator effect of sex, we will proceed with analyses in one sex only. We first tested the hypothesis that emotional eating would act as a moderator variable in that the relationship between sleep duration and increases in BMI would be stronger in participants with high than in those with low degrees of emotional eating. We next tested the hypothesis that sleep duration would act as a moderator variable in that the relationship between emotional eating and increases in BMI would be stronger in participants with short than in those with normal sleep duration. Possible mechanisms underlying a two-way emotional eating–sleep duration interaction on change in BMI will be explored by conducting mediated moderation analyses, that is an analysis on the process through which the overall moderated effect is produced.8 (p. 853) The mediating variable in these analyses is the intake of fatty/sweet food. Earlier, it was found that
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stressed emotional eaters overate on sweet and fatty food15,17,18 and that short sleep duration was associated with higher consumption of energy19 and calories from snacks20 (see Chaput and Tremblay21 for review). We first tested whether the intake of fatty/sweet food mediated the moderator effect of emotional eating on the association of short sleep duration with weight gain. We next tested whether the intake of fatty/sweet food mediated the moderator effect of sleep duration on the association of emotional eating with weight gain.
Intake of Fatty/Sweet Food In addition, in 2009 with a scale consisting of three items, we measured the intake of fatty/sweet food. The items pertained to the intake of (1) cake, (2) candy bars, and (3) chocolate; for example, “What is the number of intakes of sweet pastry, cake, or gingerbread per day?” Response categories ranged from never or less than one to seven.
Possible Confounders MATERIALS AND METHODS Participants
In addition, in 2008 we also asked questions about healthrelated lifestyle because they may act as possible confounders on our model, in that they may obscure the effects of a variable or the relationship between variables. Specifically, in single items we measured the following:
All participants in this study work at a large banking corporation in the Netherlands. Once a year the company issues a webbased lifestyle questionnaire. On the basis of their answers to the lifestyle questions, employees are offered individual feedback and lifestyle improvement advice. For the study, 8066 employees were invited to fill out the questionnaire. The present analyses are based on participants with complete information on all relevant variables in 2007, 2008, and 2009. An additional inclusion criterion was being a non-long-duration sleeper (20 cigarettes per day), (2) moderate smoking ( 0.10). There was, however, a significant positive main effect for dietary restraint on BMI change (B = 0.138 [SE = 0.061]; B`eta = 0.029; P = 0.024; more dietary restraint being associated with increases in BMI). Similarly, no significant three-way interactions were obtained for external eating: the three-way sex–external eating–sleep duration interaction on 1-year change in BMI in the initial model (no confounders) was not significant (R2 change = 0.000; F(1,1455) = 0.708; P = 0.400), and this remained so for the other models (P’s > 0.10). This time there was no significant main effect for external eating on BMI change (B = 0.112 [SE = 0.086]; B`eta = 0.016; P = 0.193 [ns]).
Emotional Eating–Sleep Duration Interaction in the Women Further Explored As recommended by Holmbeck,35 post hoc analyses on model 2 (controlling for the confounders) were conducted to determine the nature of this significant two-way emotional eating–sleep duration
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TABLE 1. Pearson Correlations of the Model Variables Split by Sex (Women: Lower Half; Men: Upper Half) 1 1. BMI change 2. Sleep duration 3. Emotional eating 4. External eating 5. Restrained eating 6. Fatty/sweet food 7. Smoking 8. Sports 9. Physical activity 10. Age 11. Education 12. General healtha
− 0.10* 0.07 0.06 0.06 − 0.06 0.01 − 0.01 − 0.03 0.08 − 0.13* 0.06
2
3
− 0.06
0.02 − 0.06
0.04 − 0.03 0.03 0.04 − 0.10* 0.04 0.01 − 0.12* − 0.01 − 0.03
0.52* 0.23* 0.15* − 0.08 − 0.05 − 0.04 − 0.13* 0.01 0.20*
4 0.00 0.02 0.55* 0.04 0.19* − 0.02 − 0.07 − 0.13* − 0.20* 0.06 0.20*
5
6
7
8
9
10
11
12
0.03 − 0.03 0.19* 0.09*
0.05 0.00 0.20* 0.26* − 0.09
− 0.04 − 0.01 − 0.10* 0.02 − 0.08* − 0.05
− 0.01 0.03 − 0.09* − 0.07 0.05 − 0.07 − 0.07
− 0.03 0.01 − 0.08 − 0.11* 0.03 − 0.03 0.00 0.26*
0.05 − 0.14* − 0.06 − 0.16* 0.09* −007 − 0.02 − 0.09* 0.13*
0.00 0.11* − 0.02 − 0.01 0.12* − 0.03 − 0.06 − 0.10* − 0.03 − 0.01
0.05 − 0.01 0.18* 0.12* 0.03 0.09* 0.03 −0.26* − 0.16* 0.05 − 0.01
− 0.11* − 0.05 0.13* 0.02 0.06 0.10* 0.03
− 0.08 − 0.09 0.03 − 0.11* 0.02 0.01
− 0.12* − 0.01 0.06 − 0.17* 0.10*
0.31* 0.04 − 0.02 − 0.27*
0.09 0.00 − 0.20*
− 0.35* 0.03
− 0.07
*P < 0.01. a A high score means poor general health. BMI, body mass index.
TABLE 2. Sex–Emotional Eating–Sleep Duration Interactions on BMI in 2009 Controlling for BMI in 2008 (BMI Change), Controlling for (1) No Confounders, (2) Age, Level of Education, Smoking, Physical Activity, and Doing Sports, (3) These Confounders Plus the Other Eating Styles, (4) These Confounders Plus (Poor) General Health, and (5) the Full Model (Unstandardized Bs) Steps
(1) No Confounders
(2) Confounders
(3)+ Eating Styles
(4) + General Health
(5) Full Model
3.644* 0.857*
3.709* 0.849* 0.014** − 0.084 0.045 − 0.112 − 0.122
3.242* 0.842* 0.016*** − 0.090 0.042 − 0.106 − 0.115 0.130 0.086
3.328* 0.842* 0.015*** − 0.072 0.082 − 0.094 − 0.135
0.162**
2.931* 0.836* 0.016*** − 0.079 0.076 − 0.091 − 0.128 0.111 0.086 0.154**
1 Intercept BMI 2008 Age Educationa Doing sports Physical activity Smoking External eating Restrained eating General healthb 2 Emotional eating 2008 Sleep duration Sexc
0.126** − 0.002*** 0.257***
0.137** − 0.002*** 0.259***
0.085 − 0.002*** 0.301***
0.117 − 0.002*** 0.251**
0.295 − 0.002*** 0.295***
Interactiond Interactione Interactionf
− 0.001 − 0.184 0.001
− 0.001 − 0.200 0.001
− 0.001 − 0.205 0.001
− 0.001 − 0.202 0.001
− 0.001 − 0.206 0.001
3
4 Interactiong
0.004**
0.004**
0.003**
0.003**
0.003**
*P < 0.0001; **P < 0.05; ***P < 0.01. a Lower education (primary school, lower vocational education, or lower general secondary education) = 1; medium education (intermediate vocational education, higher general secondary education, or pre-university education) = 2; higher education (higher vocational education or academic training) 3. b A high score means a poor general health. c 1= women; 2 = men. d Interaction between emotional eating and sleep duration. e Interaction between emotional eating and sex. f Interaction between sleep duration and sex. g Interaction between emotional eating, sleep duration, and sex. BMI, body mass index.
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Emotional Eating and Sleep Duration on Weight Gain in Female Employees
interaction on weight change in women. We first report the results with emotional eating as a possible moderator variable. The results of the regression for high emotional eating indicated that the degree of sleep duration was significantly and negatively associated with weight gain (B = −0.005; P < 0.001). In contrast, results of the regression for low emotional eating indicated that sleep duration was not significantly associated with weight gain (B = 0.000; P = 0.747). In a similar manner, we also assessed the results with sleep duration as a possible moderator variable. The results of the regression for high sleep duration indicated that the degree of emotional eating was not significantly associated with weight gain (B = −0.033; P = 0.823). In contrast, results of the regression for low sleep duration indicated that emotional eating was significantly and positively associated with weight gain (B = 0.528; P < 0.001).
Mediated Moderation We next conducted a mediated moderation analysis according to the three equations proposed by Muller et al.8 (p. 856 and p. 858) Specifically, in an analysis with emotional eating as a moderator variable (see Table 3), in Equations 1 and 2, variable X (short sleep duration; slope parameter: b11), the moderator MO (emotional eating: b12), and the XMO (short sleep duration–emotional eating interaction: b13) are regressed on the outcome variable (BMI change) and then the mediator ME (intake of fatty/sweet food; slope parameters of X, MO, and XMO, respectively: b21, b22, and b23). In Equation 3, X (b31), MO (b32), XMO (b33), ME (b34), and MEMO (b35) are regressed on the outcome variable (BMI change). According to Muller et al, 8, (p. 856) “to demonstrate mediated moderation, in [equation] 1, [b13] would be expected to be significant (the overall moderator effect on BMI change). In [equation] 2 and 3, either one or both of two patterns should exist: one of the two [b23 and b34] are significant or both [b21 and b35] are significant. And, as a result, the moderation of the residual [XMO] effect, [b33] should be reduced in magnitude (and may be nonsignificant in case of what might be called ‘full’ mediated moderation) compared to the moderation of the overall treatment effect” (in brackets: adaptations to the present equations by TvS). We first tested a mediated moderation model with emotional eating as a possible moderator variable. Specifically, we tested whether the food intake variable fatty/sweet food mediated the moderator effect of emotional eating on the association of short sleep duration with increases in BMI in the women. For these analyses we used model 2 (controlling for the possible confounders). Table 3 presents the regression models that estimate Equations 1 through 3 with these variables. In correspondence with the tables in Muller et al,8 presented here are the unstandardized coefficients (B) and their associated t statistics. As already indicated, in Equation 1, b13 was significant (B = −0.003 [SE = 0.001]; P = 0.005) (R2 change = 0.003; F(1,541) = 7.916; P = 0.005). The moderator effect was not mediated by the intake of fatty/sweet food, as b23 was not significant (P > 0.10), and b34 was only borderline significant (P = 0.064). Also, both b21 and b35 were not significant and the moderation of the residual (XMO) effect (b33) was not reduced in magnitude. (The R2 change of the XMO—emotional eating remains 0.003 (F(1,541) = 8.376; P = 0.004)—when ME and MEMO—the intake of fatty/sweet food and the intake of fatty/sweet food–emotional eating interaction—are partialled out first.) We next tested a mediated moderation model with sleep duration as a possible moderator variable. Specifically, we tested whether the food intake variable fatty/sweet food mediated the moderator effect of sleep duration on the association of emotional eating with increases in BMI in the women. Again we used model 2 (controlling for the possible confounders). Table 4 presents the regression models that estimate Equations 1 through 3 with these variables. As already indicated, in model 2, b13 was significant (B = −0.003 [SE = 0.001]; P = 0.005). The moderator effect of sleep duration on the association of emotional eating with BMI change was partly mediated by the
intake of fatty/sweet food. Both b23 and b34 were not significant (P’s > 0.10). Nevertheless, b21 was significant (B = 0.147 [SE = 0.049]; P = 0.003) and also b35 was significant (B = −0.002 [SE = 0.001]; P = 0.037). In addition, the moderation of the residual (XMO) effect (b33) was, though still significant, also somewhat reduced in magnitude. (The R2 change of the XMO—emotional eating–sleep duration interaction—was reduced from 0.003 (F(1,543) = 7.916; P = 0.005) to 0.002 (F(1,541) = 4.396; P = .035) when ME and MEMO—the intake of fatty/sweet food and the intake of fatty/sweet food–sleep duration interaction—are partialled out first.)
DISCUSSION In this study, we tested the hypothesis that the two-way emotional eating–sleep duration interaction on BMI change would be stronger in women than in men. We also tested the hypothesis that the relationship between short sleep duration and increases in BMI would depend on emotional eating. We also tested the hypothesis that the relationship between emotional eating and increases in BMI would depend on short sleep duration. Al three hypotheses were supported. The two-way emotional eating–sleep duration interaction on BMI change was present only in women but not in men. Women with higher degrees of emotional eating showed a positive and significant association between short sleep duration and increases in BMI, whereas no such association was found in women with lower degrees of emotional eating. Furthermore, women with shorter sleep duration showed a positive and significant association between emotional eating and increases in BMI, whereas no such association was found in women with a more normal sleep duration. The three-way sex–emotional eating–sleep duration interaction on change in body weight was robust for the influences of possible confounders (age, level of education, physical activity, doing sports, smoking, external eating, restrained eating, and poor general health). It also was specific for emotional eating. So, the earlier significant effect of disinhibited eating behavior on the association between short sleep duration and change in BMI in the study of Chaput et al3 was replicated in this study for emotional eating in women. The present finding in women that the association of short sleep duration with increased BMI was dependent on emotional eating (and not on restrained eating or on external eating) would suggest that poor psychological health and inadequate emotion regulation may be a possible underlying factor in this relationship. Emotional eating was earlier found to be associated with inadequate coping styles,36 depressive feelings,37 worries,38 anxiety,39 and sleep-onset latency.43 This is supported by the present finding in women that the association of emotional eating with increased BMI was dependent on short sleep duration—in itself a possible marker of psychological distress.14 At this point it should be noted that the normal and dominant response to distress is eating less because distress is normally associated with physiological reactions that are designed to prepare the individual for a fight-or-flight, response thereby suppressing hunger.40–42 By eating the same or more during distress15,17,18 emotional eaters show an abnormal or atypical stress response. Accordingly, for weight gain to occur, both short sleep duration and high emotional eating seem required, as was also supported by the present results. A further finding in the study by Chaput et al3 was that disinhibited eating also moderated the association between short sleep duration and intake of energy: only short duration sleepers with a high tendency toward disinhibition showed higher intakes of energy, whereas no association between short sleep duration and energy intake was found in people with low tendencies toward disinhibition. In this study, the intake of energy was not measured directly, so we do not know whether the moderator effect of emotional eating on the short sleep duration increase in BMI association can be attributed to a higher food intake of high emotional eaters. Nevertheless, we
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TABLE 3. Mediated Moderation With Emotional Eating as Moderator Variablea Equation 1 Criterion: BMI Change
X sleep MO emo XMO sleepemo ME fatty/sweet food MEMO fatty/sweet food emo
Equation 2 Criterion: Fatty/Sweet Food
Equation 3 Criterion: BMI Change
B
t
B
t
B
t
−0.002 (b11) 0.248 (b12) −0.003 (b13)
−2.300* 2.381* −2.813**
0.000 (b21) 0.147 (b22) 0.001 (b23)
0.354 2.989** 0.906
−0.002 (b31) 0.267 (b32) −0.004 (b33) −0.166 (b34) 0.119 (b35)
−2.269* 2.546* −2.894** −1.855 (P = 0.064) 1.144
a
Effects of the confounders not shown. *P < 0.05; **P < 0.01. BMI, body mass index; emo, emotional eating; fatty/sweet food, intake of fatty/sweet food; fatty/sweet food mo, intake of fatty/sweet food × emotional eating; ME, mediator variable; MO, moderator variable; sleep, sleep duration; sleepemo, sleep duration × emotional eating.
TABLE 4. Mediated Moderation With Sleep Duration as Moderator Variablea Equation 1 Criterion: BMI Change
X emo MO sleep XMO emosleep ME fatty/sweet food MEMO fatty/sweet food sleep
Equation 2 Criterion: Fatty/Sweet Food (Cake)
Equation 3 Criterion: BMI Change
B
t
B
t
B
t
0.248 (b11) −0.002 (b12) −0.003 (b13)
2.381* −2.300* −2.813**
0.147 (b21) 0.000 (b22) 0.001 (b23)
2.989** 0.354 0.906
0.274 (b31) −0.002 (b32) −0.003 (b33) −0.123 (b34) −0.002 (b35)
2.616** −2.399* −2.097* −1.414 −2.090*
a Effects of the confounders not shown. *P < 0.05; **P < 0.01. BMI, body mass index; emo, emotional eating; fatty/sweet food, intake of fatty/sweet food; fatty/sweet food sleep, intake of fatty/sweet food × sleep duration; ME, mediator variable; MO, moderator variable; sleep, sleep duration; emosleep, emotional eating × sleep duration.
did measure the intake of fatty/sweet food (the number of intakes of (1) sweet pastry, cake, or gingerbread, (2) candy bars, and (3) pieces of chocolate per day). Although we found no significant emotional eating–sleep duration interaction effect for the intake of fatty/sweet food, we did find a significant main effect of emotional eating on the intake of fatty/sweet food. Furthermore, although the moderator effect of emotional eating on the association of sleep duration with BMI change did not seem to be mediated by the intake of fatty/sweet food, there was some support found that the moderator effect of sleep duration on the association of emotional eating with BMI change was partly mediated by the intake of fatty/sweet food. The possibility that the intake of fatty/sweet food is (partly) intervening/mediating the mechanism that produces the moderator effect of sleep duration on the association of emotional eating with BMI change is in line with earlier findings. It may be explained by an increased appetite for food as a possible outcome of an enhanced activation of the anterior cingulated cortex (ACC), associated with both short sleep duration and high emotional eating. In an fMRI study, acute sleep deprivation was found to be associated with an increased activation in the right ACC in response to food images.43 The ACC was earlier shown to play an important role in the reward value of various foods.44 A different fMRI study showed that high emotional eaters also showed higher activation of the ACC in response to the reception of a milkshake during a negative mood compared with emotional eaters in a neutral mood.45 Similarly, a disregulated hypothalamic pituitary adrenal axis by stress may also be a possible underlying factor of the increased intake of fatty/sweet food of the high emotional eaters. High emotional eaters with a blunted cortisol 664
stress response have earlier been found to eat more food after distress than those with an elevated stress response.46 Women with high chronic stress and low cortisol stress reactivity also ate significantly more calories from chocolate cake47 and had higher scores on emotional eating in addition to a greater abdominal fatty distribution.48 Poor sleep quality (and not short sleep duration) was found to be associated with reduced cortisol stress reactivity in healthy women,49 and in children and adolescents.50 Although sleep quality and sleep quantity may be entirely unrelated, further research in this respect is needed.
STRENGTHS AND LIMITATIONS A limitation of this study concerns the use of self-reports. Employees may have underestimated their body weight and overestimated their body length. Nevertheless, we controlled BMI in 2009 for BMI in 2008, so the problem of under- or overestimation of BMI as an outcome variable may have been partly ruled out. Moreover, self-reports of variables such as sleep duration and intake of cakes may have been subject to socially desirable responding (systematic under- or overreporting). Social desirability concerns are however not limited to studies that rely on self-report measures. Concerns about the impression that one is conveying may also affect behavior in a direct test of food intake.51 A further limitation is that in this study sleep duration and BMI at T2 were measured at the same time (2009), so it was not possible to prospectively measure effects of short sleep duration on BMI changes. Another limitation is that this study did not contain a direct measure of perceived stress, only an indirect measure (sleep
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JOEM r Volume 56, Number 6, June 2014
Emotional Eating and Sleep Duration on Weight Gain in Female Employees
duration). Also, present findings are limited to the population of office workers and it is not certain that the conclusions are also applicable to the so-called blue-collar workers. A strength of the study is that, in contrast to sleep duration, BMI was prospectively measured in relation to emotional eating. A further strength is that the measurement of emotional eating took place in autumn 2008, coincidently the start of the worldwide credit crisis, which may have evoked in the employees of this bank precisely that sort of vague, unlabeled, and uncontrollable anxiety that may trigger emotional eating.11,12 The homogeneity of this sedentary population can also be regarded as a strength because it rules out individual differences in physical activity during work according to the findings.
CONCLUSIONS Only women, not men, showed a two-way emotional eating– sleep duration interaction on BMI change. Women with higher degrees of emotional eating showed a positive and significant association between short sleep duration and increases in BMI, whereas no such association was found in women with lower degrees of emotional eating. Similarly, women with shorter sleep duration showed a positive and significant association between emotional eating and increases in BMI, whereas no such association was found in women with a more normal sleep duration. The finding that the highest weight gain was found in women who combine short sleep duration with high emotional eating—both of them are a marker of (chronic) distress—would suggest that the problem of weight gain in women with short sleep duration may not be solved by simply telling them to sleep more hours.
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