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Induced dyadic stress and food intake: Examination of the moderating roles of body mass index and restraint
Eating Behaviors 23 (2016) 86–90
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Eating Behaviors
Induced dyadic stress and food intake: Examination of the moderating roles of body mass index and restraint Marilou Côté Ph.D. candidate a,⁎, Marie-Pierre Gagnon-Girouard Ph.D. a,1, Véronique Provencher Ph.D. b, Catherine Bégin Ph.D. a a b
School of Psychology, Pavillon F-A.-Savard, 2325, rue des Bibliothèques, local 1116, Laval University, Quebec, QC G1V 0A6, Canada Institute of Nutrition and Functional Foods, School of Nutrition, Pavillon des Services, 2440, boulevard Hochelaga, Laval University, Québec, QC G1V 0A6, Canada
a r t i c l e
i n f o
Article history: Received 14 March 2016 Received in revised form 20 July 2016 Accepted 23 August 2016 Available online 25 August 2016 Keywords: Induced dyadic stress Food intake Body mass index Restraint Moderated moderation Bogus taste test
a b s t r a c t Restrained eaters and overweight and obese people are prone to increase their food intake during stressful situations. This study examines the impact of a stressful couple discussion on food intake in both spouses, while simultaneously taking into account the effect of BMI and restraint on this association. For 15 min, 80 heterosexual couples discussed an aspect that they wanted their partner to change followed by an individual bogus taste test for the purpose of measuring his or her stress-induced food intake. Prior to and after the discussion, subjective mood state was assessed, as well as appetite perceptions, and the mood change before and after the discussion was calculated. Multiple regression analyses with a three-way interaction between mood change, BMI, and restraint were used to predict food intake for both men and women, while controlling for appetite perceptions. Only restrained women with a high BMI ate more when their mood worsened. For men, only appetite perceptions significantly predicted food intake. These results suggest that an induced negative mood in the form of a stressful couple discussion impacts food intake differently for men and women, and that particular attention should be given to the concomitant effect of both restraint and BMI when studying stress-induced eating among women. © 2016 Elsevier Ltd. All rights reserved.
1. Introduction The relationship between stress, negative affect and food intake is complex. A review of experimental studies examining the association between stress and eating among normal-eaters indicated that around 40% of these studies reported an increase in food intake when emotions/stress were induced, whereas 35% reported a decrease and 25% reported no change in food intake (Macht, 2008). To deepen our understanding of how emotions affect eating, Macht (2008) conceptualized a five-way model. According to this model, the relationship between emotion and eating varies according to individual characteristics (being a restrained eater or an emotional eater) as well as emotion characteristics (valence, arousal and intensity). More specifically, regarding emotion characteristics, Macht (2008) proposes that higharousal or intense emotions inhibit food intake since the physiological stress-response interferes with appetite and eating, while low-arousal ⁎ Corresponding author at: 2325, rue des Bibliothèques, local 1116, Québec, QC G1V 0A6, Canada. E-mail addresses: [email protected] (M. Côté), [email protected] (M.-P. Gagnon-Girouard), [email protected] (V. Provencher), [email protected] (C. Bégin). 1 Present address: Psychology Department, 3351 boulevard des Forges, C.P. 500, Pavillon Michel-Sarrazin, Université du Québec à Trois-Rivières, Trois-Rivières (Québec), Canada, G9A 5H7.
http://dx.doi.org/10.1016/j.eatbeh.2016.08.006 1471-0153/© 2016 Elsevier Ltd. All rights reserved.
emotions do not affect eating. However, moderate-arousal emotions can increase or decrease food intake depending on individual characteristics, one of them being restrained eating. Restrained eaters are defined as individuals who apply self-imposed rules to control food intake in order to lose or to maintain weight (Herman & Polivy, 2005). Usually identified by the Restraint Scale (Herman & Polivy, 1980), restrained eaters increase their food intake in response to stress and negative affect compared to unrestrained eaters, both in laboratory (Cools, Schotte, & McNally, 1992; Schotte, Cools, & McNally, 1990; Polivy, Herman, & Mcfarlane, 1994) and reallife settings (Wardle, Steptoe, Oliver, & Lipsey, 2000). Many hypotheses have been formulated to explain those findings. One of them, the limited capacity hypothesis, stipulates that, when facing stress or negative affect, restrained eaters are no longer able to control their food intake since coping with these negative affects requires a significant amount of cognitive resources which deplete those usually used to maintain dietary restraint (Boon, Stroebe, Schut, & Ijntema, 2002). This assumption is supported by experimental studies where restrained eaters significantly increased their food intake when exposed to a high cognitive load/distraction as compared to unrestrained eaters (Lattimore & Caswell, 2004; Ward & Mann, 2000), especially when the cognitive load involves an ego-threat (Lattimore & Maxwell, 2004). The impact of weight on the relationship between stress and food intake has also been studied extensively. A 9-year longitudinal study
M. Côté et al. / Eating Behaviors 23 (2016) 86–90
showed that psychosocial stress is associated with greater weight gain among individuals with a higher baseline body mass index (BMI) as compared with individuals with a lower baseline BMI (Ayanian, Block, He, Zaslavsky, & Ding, 2009). Some laboratory studies also indicated that overweight and obese individuals eat more in response to stress and negative affect compared to normal-weight individuals (Slochower, Kaplan, & Mann, 1981; McKenna, 1972). Recently, Lemmens, Rutters, Born, and Westerterp-Plantenga (2011) showed that participants with abdominal obesity increased their food intake by approximately 6% in a stress condition compared to a rest condition and in contrast to normal-weight participants whose food intake was not affected by stress. Spouses' interactions are an important source of stress. A discussion between spouses can lead to an increase in emotional arousal and negative affect as well as physiological arousal (Nealey-Moore, Smith, Uchino, Hawkins, & Olson-Cerny, 2007; Verhofstadt, Buysse, De Clercq, & Goodwin, 2005). Laboratory research has demonstrated that, following a negative marital discussion, men and women experience an increase in systolic blood pressure and heart rate, as well as a greater cortisol response (Kiecolt-Glaser et al., 1993; Nealey-Moore et al., 2007; Saxbe & Repetti, 2010). Therefore, couple interactions could act as an interpersonal stressor that could trigger disinhibited eating. However, to our knowledge, no study has examined the relationship between experimentally induced dyadic stress through a negative couple discussion and food intake in a laboratory setting. Hence, the aim of the present study was to investigate the impact of an experimentally induced stressful couple discussion on food intake in both spouses, while simultaneously taking into account the possible moderating effects of BMI and restraint. It was hypothesized that the relationship between mood change following the couple discussion and food intake would be moderated by BMI and restraint, with higher BMI and restraint having a greater disinhibiting effect on food intake. 2. Methods 2.1. Participants Eighty heterosexual couples were recruited through email lists from Laval University as well as from a research volunteer list from the general community of Quebec City. Inclusion criteria were: 1) being 18 years or older, and 2) cohabiting for at least six months. People suffering from food allergies related to the items presented during the taste test as well as those with diabetes were excluded from the study. Women's age ranged from 18 to 73 years (M = 31.35, SD = 13.69) and men's age ranged from 19 to 74 years (M = 33.78, SD = 14.14). Relationship duration ranged from nine months to 53 years (M = 7.48, SD = 10.15). Women's BMI ranged from 17.3 to 43.9 (M = 24.26, SD = 4.31) and men's BMI ranged from 15.9 to 38.6 (M = 25, SD = 4.12). Demographic characteristics of the sample are described in Table 1. 2.2. Procedure Participants were invited to take part in a study examining the impact of stress experienced during a couple discussion on food taste. In order to accommodate the largest number of couples, appointments were scheduled at different times of the day (18% morning, 36% afternoon and 46% evening).2 Participants were instructed to abstain from eating 2 h prior the experiment. At their arrival, partners were separated and each partner was asked to rate their mood using a visual analogue scale (VAS). Afterwards, they were instructed to write a list of at least one aspect of their partner's behavior or attitude that they would like him or her to change. It was 2 A one-way ANOVA revealed no significant difference on total food intake according to the moment of the experiment (p N 0.05).
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Table 1 Demographic characteristics by sex.
Marital status Married Free union First language French English Other Ethnicity Caucasian (White) African American (Black) Native Asian Latin Other Occupation* Full-time student Part-time student Full-time worker Part-time worker Seasonal worker Self-employed Unemployed At home parent Retired Education High-school College University Annual household income 0–19,999$ 20,000–39,999$ 40,000–59,999$ 60,000–79,999$ 80,000–99,999$ 100,000 and higher Would rather not answer
Women (n = 80)
Men (n = 80)
% (n)
% (n)
25 (20) 75 (60)
25 (20) 75 (60)
92.4 (74) 1.3 (1) 6.3 (5)
92.4 (74) 1.3 (1) 6.3 (5)
91.3 (73) 1.3 (1) 1.3 (1) 1.3 (1) 1.3 (1) 3.8 (3)
92.5 (74) 2.5 (2) 0 (0) 0 (0) 2.5 (2) 2.5 (2)
55 (44) 10 (8) 26.3 (21) 20 (16) 0 (0) 3.8 (3) 1.3 (1) 1.3 (1) 8.8 (7)
42.5 (34) 2.5 (2) 40 (32) 6.3 (5) 6.3 (5) 5 (4) 5 (4) 0 (0) 8.8 (7)
0 (0) 42.5 (34) 57.5 (46)
17.5 (14) 30 (24) 52.5 (42)
38.8 (31) 21.3 (17) 7.5 (6) 7.5 (6) 8.8 (7) 8.8 (7) 7.5 (6)
28.7 (23) 27.5 (22) 11.3 (9) 13.8 (11) 10 (8) 7.5 (6) 1.3 (1)
⁎ Participants were allowed to endorse more than one occupation.
specified that the issues should be specific and framed respectfully (inspired from Van den Broucke, Vandereycken, & Vertommen, 1995). Partners were then brought into the same room and instructed to discuss these issues for 15 min. They were told that both of them must address at least one point on their list, and to continue discussing even if they talked about every point; they were free to generate new ideas as long as they remained within the suggested theme. To reproduce as much as possible a real-life couple discussion, no other rule was given for the discussion, each partner was free to talk as much points and as much long as he or she wanted. Discussions were videotaped to ensure that all participants adhered to the instructions. After the discussion, the partners were separated and asked to rate their mood again. They were also asked to assess their appetite perceptions. Next, a bogus taste test was introduced. As participants were recruited to take part in a study examining the impact of stress on food taste, they ignored that the amount of food eaten would be measured. Pre-weighed food was presented uniformly to participants and they were told to taste at least one bite of each food item in order to complete the taste test (see Section 2.3.4. Bogus taste test). They were told to eat as much as they wanted since the food was prepared just for them. Participants were alone in the room while completing the 10-min taste test. Afterwards, the leftover food was weighed using the same calibrated scale. Participants were then instructed to complete the questionnaires. Finally, both partners were brought together for the debriefing session. They were probed for suspicions about the true purpose of the experiment; none guessed that the amount of food eaten was measured. A second informed consent was signed. Objective measures of height and weight were taken.
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2.3. Measures 2.3.1. Mood Participants' mood was assessed before and after the discussion with the following statement: “Altogether my mood at the moment is…” on a 150 mm VAS on which the end points were labeled “very good” and “very bad” (based on Dingemans, Martijn, Jansen, & van Furth, 2009). Mood change was calculated by subtracting the mood evaluation before the discussion from the mood evaluation after the discussion. 2.3.2. Appetite perceptions Appetite was evaluated with four 150 mm VAS: desire to eat, hunger, fullness, and prospective food consumption (Hill & Blundell, 1986). For example, hunger was evaluated with the question: “How hungry do you feel?” The end points were labeled “Not hungry at all” and “Very hungry”. A total appetite perceptions score was obtained by calculating the mean of four items (reversed score for fullness). 2.3.3. Restrained eating Restrained eating was measured by the Revised Restraint Scale (Herman & Polivy, 1980). This 10-item scale measures restrained eating and has two subscales: concern for dieting and weight fluctuation. It has good psychometric properties (Laessle, Tuschl, Kotthaus, & Pirke, 1989). The Cronbach's alpha in the present study was 0.78, which is sufficient. 2.3.4. Bogus taste test All participants were presented with four bowls containing 200 g of milk chocolate M&M, 60 g of classic Lay's chips, 120 g of Teddy Graham vanilla cookies, and 100 g of house brand salted pretzels. All food items were removed from their original packaging, and uniformly presented in four separate clear bowls placed on a plastic tray. Participants were asked to taste and rate each food using VAS (e.g., To what extent is it salty?). Total food intake in grams was determined by subtracting the weight of the leftover food from the pre-weighed food for each food item and then calculating the sum of those differences.3 2.3.5. BMI Participants' height and weight were measured and BMI (kg/m2) was calculated. 2.4. Statistical analysis Analyses were carried out using SPSS version 20.0. A manipulation check for mood change was performed using a 2 (time) × 2 (sex) repeated-measures analysis of variance. A multivariate analysis of variance (MANOVA) was performed to examine mean differences among women and men with respect to food intake, restraint score (RS), BMI, and appetite. In order to test the moderating effect of BMI and RS on the relationship between food intake and mood change, multiple regression analyses with three-way interactions were performed separately for men and women using model three of the PROCESS macro developed by Hayes (2013). PROCESS calculates all the necessary products, estimates the best-fitting ordinary least squares regression model, and tests the three-way interaction (Hayes, 2013). A significant moderated moderation effect would be demonstrated by a significant three-way interaction, regardless if there was or was not a main effect for the independent variable (mood change) or the moderator variables (BMI and RS). In the case of a significant interaction, PROCESS would produce the simple slopes at −1, 0, and 1 standard deviation (SD) of the moderators (BMI and RS) when estimating the conditional effect (CE) of the 3 Total caloric intake was also calculated, and was highly correlated with intake in grams (r = 0.997; n = 160). Thereby, food intake was reported in grams in the following analyses.
independent variable (mood change) on dependent variable (food intake). Prior to analyses, variables were z-standardized, and correlations between food intake and potential covariates (appetite perceptions and relationship duration) were tested. Furthermore, the dependent variable (food intake) was inspected for outliers. All values located above the 97th percentile of the distribution (n = 4) were winsorized to bring them to the 97th percentile. All independent variables were screened for potential multivariate outliers. Two cases among women and three among men were identified through Mahalanobis distance as multivariate outliers (p b 0.001). Since there was no difference in the pattern of results among men when the three outliers were included, the analyses will include the outliers to maximize statistical power. In contrast, the two outliers changed the pattern of results for women and thus were not included in the analyses. Also, two additional participants were dropped from analyses because of missing data. The analysed sample consisted of 79 men and 77 women. 3. Results 3.1. Manipulation check of mood The manipulation check yielded a significant time by sex interaction, F(1, 78) = 6.46, p = 0.013, η2 = 0.076. Although men experienced a worsening of mood (before the discussion: M = 3.25, SD = 2.92; after the discussion: M = 3.46, SD = 2.89), post-hoc pairwise comparisons indicated that the effect of time, i.e., mood change, was significant only among women, F(1, 78) = 15.92, p b 0.001 (before the discussion: M = 2.71, SD = 2.52; after the discussion: M = 3.84, SD = 2.99). 3.2. Sex differences Results of the MANOVA revealed a significant multivariate effect indicating a significant sex difference, Wilks' λ = 0.662, F(5, 150) = 15.31, p b 0.001. Given the significance of the overall test, the univariate main effects were examined. They yielded a significant sex difference for food intake, F(1, 150) = 16.48, p b 0.001, and RS F(1, 150) = 16.07, p b 0.001. Men ate significantly more than women (respectively, M = 83.78, SD = 36.39; M = 61.86, SD = 30.72), while women reported significantly higher RS than men (respectively, M = 13.06, SD = 5.07; M = 9.68, SD = 5.45). No difference was noted for BMI and appetite perceptions. 3.3. Relationship between mood change and food intake Since appetite perceptions was significantly correlated with food intake among men and women (respectively, r = 0.461, p b 0.001; r = 0.283, p = 0.012), it was entered in the equation as a covariate. Relationship duration was not correlated with women's food intake, but was significantly correlated with men's food intake. It was not included as a covariate in the final model since it did not significantly add to the model. Among women, the overall multiple linear regression model was significant and accounted for 30% of the variance in food intake, R2 = 0.30, F(8, 68) = 3.61, p = 0.002. Table 2 shows that the three-way interaction between mood change, BMI and RS was a significant predictor of food intake. That is, BMI moderated the effect of mood change on food intake while RS moderated the moderating effect of BMI. Fig. 1 illustrates the three-way interaction. Examination of the interaction indicated that women who presented both high RS and high BMI (one SD above the mean) ate significantly more when their mood worsened (CE = 0.4348, p = 0.02). For all other women, there was no significant effect of mood change on food intake, with non-significant CEs of BMI and RS (all p N 0.05). The Johnson-Neyman technique (Johnson & Neyman, 1936) was used to determine the value of RS at which the interaction became significant. At
M. Côté et al. / Eating Behaviors 23 (2016) 86–90 Table 2 Multiple regression models predicting the effect of mood change on food intake in women and men.
Women
Men
Predictors
β
t VALUE
p
Mood BMI RS Mood × BMI Mood × RS BMI × RS Mood × BMI × RS Appetite† Mood BMI RS Mood × BMI Mood × RS BMI × RS Mood × BMI × RS Appetite†
−0.0597 −0.0191 0.2181 0.2833 −0.0318 0.1947 0.3643 0.3305 0.1567 0.0068 0.1690 −0.0494 −0.0240 0.1168 0.0047 0.1408
−0.3997 −0.1047 1.5166 1.1600 −0.1818 1.6844 2.1399 3.0948 1.4300 0.0540 1.2418 −0.2592 −0.1406 1.0332 0.0289 4.8507
0.6907 0.9169 0.1340 0.2501 0.8563 0.0967 0.0360⁎ 0.0029⁎⁎ 0.1572 0.9571 0.2184 0.7963 0.8886 0.3051 0.9770 0.0000⁎⁎⁎
Note: Women: n = 77; Men: n = 79. ⁎ p b 0.05 ⁎⁎ p b 0.01 ⁎⁎⁎ p b 0.001. † Covariate.
the 0.05 alpha level, women with a RS of 15.51 or higher ate significantly more as their mood worsened, which is consistent with the existing literature which propose a cut-off score of 15 or more to classify restrained eaters (Goldman, Herman, & Polivy, 1991; Polivy, Herman, & Deo, 2010). Among men, the overall multiple linear regression model was also significant and accounted for 31% of the variance in food intake, R2 = 0.31, F(8, 70) = 3.99, p = 0.001. There was no significant main effect of mood change on food intake, nor any significant interaction (Table 2). Only appetite perceptions was found to be a significant predictor of food intake in men (p b 0.001). 4. Discussion The aim of the present study was to investigate the impact of an experimental negative mood induction, in the form of a stressful couple discussion, on food intake in both partners, while taking into account the possible moderating effects of BMI and restraint. The initial hypothesis concerning the simultaneous moderating effects of BMI and restraint on the relationship between mood change and food intake was confirmed among women. More specifically, the mood worsening induced by the stressful couple discussion led to an increase in food intake 1.5
RS=-1, BMI=-1 RS=1, BMI=-1
RS=-1, BMI=1 RS=1, BMI=1
1 y = 0,4349x + 0,3723*
Food intake
0.5 y = 0.0375x - 0.0182 0 y = -0.0856x - 0.3786
-0.5
y = -0.708x + 0.0561 -1 -1.5 -2
Low mood change
High mood change
Fig. 1. Interaction plot showing associations between subjective mood change and food intake for women at different values of restraint as measured by the Restraint Scale score and body mass index (BMI). All variables are z-standardized. 1: One standard deviation above the mean; −1: One standard deviation under the mean.
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only among restrained women with a high BMI. The observation of the simultaneous effect of BMI and restraint on measured food intake following an induced negative mood is an important contribution of the present study. To our knowledge, no other study on stress-induced eating has examined their concomitant effect on food intake. Results support previous studies showing that overweight women (Lemmens et al., 2011; Slochower et al., 1981) and women with high scores on the Restraint Scale (Cools et al., 1992; Schotte et al., 1990; Tanofsky-Kraff, Wilfley, & Spurrell, 2000) are more prone to disinhibited eating when facing stress and negative emotion. However, in the present study, neither restrained eating nor BMI alone accounted for the association between mood and food intake. It was rather the interaction between both high restraint and high BMI that predicted women's greater food intake following their negative mood change. One possible explanation for the complex relationship observed herein is the inclusion of women from the general population. Indeed, about the half of our sample consisted of people from the general population (the other half consisted of student), whereas most stress-induced eating studies use samples comprised uniquely of female college students (e.g., Cools et al., 1992; Schotte et al., 1990; Tanofsky-Kraff et al., 2000). In fact, the relationship between weight and restrained eating observed among the general population differs from what is observed among college students. For example, in our sample, 67% of overweight/obese women were restrained eaters compared to 18% of normal-weight women. In female college students, only 33% of overweight/obese students were identified as restrained eaters compared to 50% of normalweight students (Rand & Kuldau, 1991). It might be that as women get older, restraint is more tightly linked to overweight and obesity, explaining the observed interaction effect. Longitudinal studies have shown that, in the long term, unsuccessful restrained eating is associated with an increase in BMI, especially among women (Drapeau et al., 2003; van Strien, Herman, & Verheijden, 2014). It is possible that overtime it becomes increasingly difficult for women to maintain strict dietary restraint, making them more prone to transgress their dietary rules, which could lead to weight gain (Polivy, 1996; van Strien et al., 2014). Sex comparisons showed that men and women react quite differently when facing a dyadic stressor. First, the mood of the women was more affected by the stressful couple discussion. These results are not surprising since women tend to show a greater physiological reaction to a stressful couple discussion than men (Kiecolt-Glaser & Newton, 2001). Second, food intake was not explained by the same variables for men and women. Indeed, even though men ate significantly more than women, the moderating effect of restraint and BMI on the relationship between mood change and food intake was not found among men. In fact, men ate mostly based on their appetite perceptions. These results are coherent with evidence showing that men have greater caloric needs (Kiefer, Rathmanner, & Kunze, 2005), and eat more intuitively, i.e., in response to hunger and satiety cues, than women (Denny, Loth, Eisenberg, & Neumark-Sztainer, 2013; Smith & Hawks, 2006). This specific sex difference can also be explained by the fact that men had significantly lower levels of restraint than women, as usually observed in other studies (Kiefer et al., 2005; Rand & Kuldau, 1991). Since men are known to be less preoccupied with their weight than women (Forrester-Knauss & Zemp Stutz, 2012; Rolls, Fedoroff, & Guthrie, 1991), it is not surprising that their food intake was determined by their appetite perceptions rather than by mood, especially since their mood did not significantly worsen following the stressful discussion. Although the findings of the present study propose significant contributions to the stress-induced eating literature, their limitations should be stated. First, in order to reproduce as close as possible the realism of a real-life couple discussion, no rule was given to participants about speaking turns during the discussion. The only aspect mentioned was that both partners had to address at least one aspect they would like their partner to change. Although this may contribute positively to the external validity of the study, it could be hypothesized that unequal talking turns could have influenced partners' mood (e.g., being
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mostly on the receiving end of the discussion could have been more stressful), which could explain the difference found between men and women regarding mood change following the discussion. Furthermore, for reasons of cost and achievability, self-reported mood VAS was used to measure stress. Physiological measures such as cortisol rates, blood pressure and heart rate would have been more objective ways to measure stress. Because physiological measures generally fall outside the scope of consciousness and are not impacted by social desirability, they may be more accurate to assess stress (Rutledge & Linden, 1998). 5. Conclusions To conclude, the findings of the present study support the complex relationship between stress and eating and provide a better understanding of the effect of gender, restraint and BMI on this relationship. A stressful couple discussion led restrained women with a high BMI to greater food intake. Considering that dyadic stress is part of everyday life for many couples, the results of the present study suggest that it is relevant to sensitize women struggling with weight issues about the potentially deleterious effect of a discrete episode of dyadic stress on their eating behaviors. Contributors All authors contributed to the design of the study. Author Côté wrote the protocol, conducted literature searches and statistical analysis, and wrote the first draft of the manuscript. All authors contributed to and have approved the final manuscript. Conflict of interest All authors declare that they have no conflicts of interest. Acknowledgments We thank Hélène Paradis for statistical analysis guidance, as well as Annette Gallant for language editing. We also thank the Centre de recherche interdisciplinaire sur les problèmes conjugaux et les agressions sexuelles (CRIPCAS) for funding support.
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Differential effects of active and passive stress on food intake in restrained and unrestrained eaters. Appetite, 42(2), 167–173. http://dx.doi. org/10.1016/j.appet.2003.09.002. Lattimore, P., & Maxwell, L. (2004). Cognitive load, stress, and disinhibited eating. Eating Behaviors, 5(4), 315–324. http://dx.doi.org/10.1016/j.eatbeh.2004.04.009. Lemmens, S. G., Rutters, F., Born, J. M., & Westerterp-Plantenga, M. S. (2011). Stress augments food “wanting” and energy intake in visceral overweight subjects in the absence of hunger. Physiology & Behavior, 103(2), 157–163. http://dx.doi.org/10.1016/ j.physbeh.2011.01.009. Macht, M. (2008). How emotions affect eating: A five-way model. Appetite, 50(1), 1–11. http://dx.doi.org/10.1016/j.appet.2007.07.002. McKenna, R. J. (1972). Some effects of anxiety level and food cues on the eating behavior of obese and normal subjects: A comparison of the Schachterian and psychosomatic conceptions. Journal of Personality and Social Psychology, 22(3), 311–319 (Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/5047384). Nealey-Moore, J. B., Smith, T. W., Uchino, B. N., Hawkins, M. W., & Olson-Cerny, C. (2007). Cardiovascular reactivity during positive and negative marital interactions. Journal of Behavioral Medicine, 30(6), 505–519. http://dx.doi.org/10.1007/s10865-007-9124-5. Polivy, J. (1996). Psychological consequences of food restriction. Journal of the American Dietetic Association, 96(6), 589–592. http://dx.doi.org/10.1016/S0002-8223(96)00161-7. Polivy, J., Herman, C. P., & Deo, R. (2010). Getting a bigger slice of the pie. Effects on eating and emotion in restrained and unrestrained eaters. Appetite, 55(3), 426–430. http:// dx.doi.org/10.1016/j.appet.2010.07.015. Polivy, J., Herman, C. P., & Mcfarlane, T. (1994). Effects of anxiety on eating: Does palatability moderate distress-induced overeating in dieters? Journal of Abnormal Psychology, 103(3), 505–510. http://dx.doi.org/10.1037/0021-843X.103.3.505. Rand, C. S. W., & Kuldau, J. M. (1991). Restrained eating (weight concerns) in the general population and among students. International Journal of Eating Disorders, 11(6), 699–708. http://dx.doi.org/10.1002/1098-108X(199111)10: 6b699::AID-EAT2260100608N3.0.CO;2-0. Rolls, B. J., Fedoroff, I. C., & Guthrie, J. F. (1991). Gender differences in eating behavior and body weight regulation. Health Psychology, 10(2), 133–142. http://dx.doi.org/10. 1037/0278-6133.10.2.133. Rutledge, T., & Linden, W. (1998). To eat or not to eat: Affective and physiological mechanisms in the stress-eating relationship. Journal of Behavioral Medicine, 21(3), 221–240. http://dx.doi.org/10.1023/A:1018784015771. Saxbe, D., & Repetti, R. L. (2010). For better or worse? Coregulation of couples' cortisol levels and mood states. Journal of Personality and Social Psychology, 98(1), 92–103. http://dx.doi.org/10.1037/a0016959. Schotte, D. E., Cools, J., & McNally, R. J. (1990). Film-induced negative affect triggers overeating in restrained eaters. Journal of Abnormal Psychology, 99(3), 317–320. http://dx. doi.org/10.1037/0021-843X.99.3.317. Slochower, J., Kaplan, S. P., & Mann, L. (1981). The effects of life stress and weight on mood and eating. Appetite, 2(2), 115–125. http://dx.doi.org/10.1016/S01956663(81)80005-0. Smith, T., & Hawks, S. R. (2006). Intuitive eating, diet composition, and the meaning of food in healthy weight promotion. American Journal of Health Education, 37(3), 130–136. http://dx.doi.org/10.1080/19325037.2006.10598892. Tanofsky-Kraff, M., Wilfley, D. E., & Spurrell, E. (2000). Impact of interpersonal and egorelated stress on restrained eaters. The International Journal of Eating Disorders, 27(4), 411–418. http://dx.doi.org/10.1002/(SICI)1098-108X(200005)27:4b411:: AID-EAT5N3.0.CO;2-P. Van den Broucke, S., Vandereycken, W., & Vertommen, H. (1995). Marital communication in eating disorder patients: A controlled observational study. The International Journal of Eating Disorders, 17(1), 1–21. http://dx.doi.org/10.1002/1098-108X(199501)17: 1b1::AID-EAT2260170102N3.0.CO;2-3. Van Strien, T., Herman, C. P., & Verheijden, M. W. (2014). Dietary restraint and body mass change. A 3-year follow up study in a representative Dutch sample. Appetite, 76, 44–49. http://dx.doi.org/10.1016/j.appet.2014.01.015. Verhofstadt, L. L., Buysse, A., De Clercq, A., & Goodwin, R. (2005). Emotional arousal and negative affect in marital conflict: The influence of gender, conflict structure, and demand-withdrawal. European Journal of Social Psychology, 467(December 2004), 449–467. http://dx.doi.org/10.1002/ejsp.262. Ward, A., & Mann, T. (2000). Don't mind if I do: Disinhibited eating under cognitive load. Journal of Personality and Social Psychology, 78(4), 753–763. http://dx.doi.org/10. 1037/0022-3514.78.4.753. Wardle, J., Steptoe, A., Oliver, G., & Lipsey, Z. (2000). Stress, dietary restraint and food intake. Journal of Psychosomatic Research, 48(2), 195–202. http://dx.doi.org/10.1016/ S0022-3999(00)00076-3.
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Eating Behaviors
Induced dyadic stress and food intake: Examination of the moderating roles of body mass index and restraint Marilou Côté Ph.D. candidate a,⁎, Marie-Pierre Gagnon-Girouard Ph.D. a,1, Véronique Provencher Ph.D. b, Catherine Bégin Ph.D. a a b
School of Psychology, Pavillon F-A.-Savard, 2325, rue des Bibliothèques, local 1116, Laval University, Quebec, QC G1V 0A6, Canada Institute of Nutrition and Functional Foods, School of Nutrition, Pavillon des Services, 2440, boulevard Hochelaga, Laval University, Québec, QC G1V 0A6, Canada
a r t i c l e
i n f o
Article history: Received 14 March 2016 Received in revised form 20 July 2016 Accepted 23 August 2016 Available online 25 August 2016 Keywords: Induced dyadic stress Food intake Body mass index Restraint Moderated moderation Bogus taste test
a b s t r a c t Restrained eaters and overweight and obese people are prone to increase their food intake during stressful situations. This study examines the impact of a stressful couple discussion on food intake in both spouses, while simultaneously taking into account the effect of BMI and restraint on this association. For 15 min, 80 heterosexual couples discussed an aspect that they wanted their partner to change followed by an individual bogus taste test for the purpose of measuring his or her stress-induced food intake. Prior to and after the discussion, subjective mood state was assessed, as well as appetite perceptions, and the mood change before and after the discussion was calculated. Multiple regression analyses with a three-way interaction between mood change, BMI, and restraint were used to predict food intake for both men and women, while controlling for appetite perceptions. Only restrained women with a high BMI ate more when their mood worsened. For men, only appetite perceptions significantly predicted food intake. These results suggest that an induced negative mood in the form of a stressful couple discussion impacts food intake differently for men and women, and that particular attention should be given to the concomitant effect of both restraint and BMI when studying stress-induced eating among women. © 2016 Elsevier Ltd. All rights reserved.
1. Introduction The relationship between stress, negative affect and food intake is complex. A review of experimental studies examining the association between stress and eating among normal-eaters indicated that around 40% of these studies reported an increase in food intake when emotions/stress were induced, whereas 35% reported a decrease and 25% reported no change in food intake (Macht, 2008). To deepen our understanding of how emotions affect eating, Macht (2008) conceptualized a five-way model. According to this model, the relationship between emotion and eating varies according to individual characteristics (being a restrained eater or an emotional eater) as well as emotion characteristics (valence, arousal and intensity). More specifically, regarding emotion characteristics, Macht (2008) proposes that higharousal or intense emotions inhibit food intake since the physiological stress-response interferes with appetite and eating, while low-arousal ⁎ Corresponding author at: 2325, rue des Bibliothèques, local 1116, Québec, QC G1V 0A6, Canada. E-mail addresses: [email protected] (M. Côté), [email protected] (M.-P. Gagnon-Girouard), [email protected] (V. Provencher), [email protected] (C. Bégin). 1 Present address: Psychology Department, 3351 boulevard des Forges, C.P. 500, Pavillon Michel-Sarrazin, Université du Québec à Trois-Rivières, Trois-Rivières (Québec), Canada, G9A 5H7.
http://dx.doi.org/10.1016/j.eatbeh.2016.08.006 1471-0153/© 2016 Elsevier Ltd. All rights reserved.
emotions do not affect eating. However, moderate-arousal emotions can increase or decrease food intake depending on individual characteristics, one of them being restrained eating. Restrained eaters are defined as individuals who apply self-imposed rules to control food intake in order to lose or to maintain weight (Herman & Polivy, 2005). Usually identified by the Restraint Scale (Herman & Polivy, 1980), restrained eaters increase their food intake in response to stress and negative affect compared to unrestrained eaters, both in laboratory (Cools, Schotte, & McNally, 1992; Schotte, Cools, & McNally, 1990; Polivy, Herman, & Mcfarlane, 1994) and reallife settings (Wardle, Steptoe, Oliver, & Lipsey, 2000). Many hypotheses have been formulated to explain those findings. One of them, the limited capacity hypothesis, stipulates that, when facing stress or negative affect, restrained eaters are no longer able to control their food intake since coping with these negative affects requires a significant amount of cognitive resources which deplete those usually used to maintain dietary restraint (Boon, Stroebe, Schut, & Ijntema, 2002). This assumption is supported by experimental studies where restrained eaters significantly increased their food intake when exposed to a high cognitive load/distraction as compared to unrestrained eaters (Lattimore & Caswell, 2004; Ward & Mann, 2000), especially when the cognitive load involves an ego-threat (Lattimore & Maxwell, 2004). The impact of weight on the relationship between stress and food intake has also been studied extensively. A 9-year longitudinal study
M. Côté et al. / Eating Behaviors 23 (2016) 86–90
showed that psychosocial stress is associated with greater weight gain among individuals with a higher baseline body mass index (BMI) as compared with individuals with a lower baseline BMI (Ayanian, Block, He, Zaslavsky, & Ding, 2009). Some laboratory studies also indicated that overweight and obese individuals eat more in response to stress and negative affect compared to normal-weight individuals (Slochower, Kaplan, & Mann, 1981; McKenna, 1972). Recently, Lemmens, Rutters, Born, and Westerterp-Plantenga (2011) showed that participants with abdominal obesity increased their food intake by approximately 6% in a stress condition compared to a rest condition and in contrast to normal-weight participants whose food intake was not affected by stress. Spouses' interactions are an important source of stress. A discussion between spouses can lead to an increase in emotional arousal and negative affect as well as physiological arousal (Nealey-Moore, Smith, Uchino, Hawkins, & Olson-Cerny, 2007; Verhofstadt, Buysse, De Clercq, & Goodwin, 2005). Laboratory research has demonstrated that, following a negative marital discussion, men and women experience an increase in systolic blood pressure and heart rate, as well as a greater cortisol response (Kiecolt-Glaser et al., 1993; Nealey-Moore et al., 2007; Saxbe & Repetti, 2010). Therefore, couple interactions could act as an interpersonal stressor that could trigger disinhibited eating. However, to our knowledge, no study has examined the relationship between experimentally induced dyadic stress through a negative couple discussion and food intake in a laboratory setting. Hence, the aim of the present study was to investigate the impact of an experimentally induced stressful couple discussion on food intake in both spouses, while simultaneously taking into account the possible moderating effects of BMI and restraint. It was hypothesized that the relationship between mood change following the couple discussion and food intake would be moderated by BMI and restraint, with higher BMI and restraint having a greater disinhibiting effect on food intake. 2. Methods 2.1. Participants Eighty heterosexual couples were recruited through email lists from Laval University as well as from a research volunteer list from the general community of Quebec City. Inclusion criteria were: 1) being 18 years or older, and 2) cohabiting for at least six months. People suffering from food allergies related to the items presented during the taste test as well as those with diabetes were excluded from the study. Women's age ranged from 18 to 73 years (M = 31.35, SD = 13.69) and men's age ranged from 19 to 74 years (M = 33.78, SD = 14.14). Relationship duration ranged from nine months to 53 years (M = 7.48, SD = 10.15). Women's BMI ranged from 17.3 to 43.9 (M = 24.26, SD = 4.31) and men's BMI ranged from 15.9 to 38.6 (M = 25, SD = 4.12). Demographic characteristics of the sample are described in Table 1. 2.2. Procedure Participants were invited to take part in a study examining the impact of stress experienced during a couple discussion on food taste. In order to accommodate the largest number of couples, appointments were scheduled at different times of the day (18% morning, 36% afternoon and 46% evening).2 Participants were instructed to abstain from eating 2 h prior the experiment. At their arrival, partners were separated and each partner was asked to rate their mood using a visual analogue scale (VAS). Afterwards, they were instructed to write a list of at least one aspect of their partner's behavior or attitude that they would like him or her to change. It was 2 A one-way ANOVA revealed no significant difference on total food intake according to the moment of the experiment (p N 0.05).
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Table 1 Demographic characteristics by sex.
Marital status Married Free union First language French English Other Ethnicity Caucasian (White) African American (Black) Native Asian Latin Other Occupation* Full-time student Part-time student Full-time worker Part-time worker Seasonal worker Self-employed Unemployed At home parent Retired Education High-school College University Annual household income 0–19,999$ 20,000–39,999$ 40,000–59,999$ 60,000–79,999$ 80,000–99,999$ 100,000 and higher Would rather not answer
Women (n = 80)
Men (n = 80)
% (n)
% (n)
25 (20) 75 (60)
25 (20) 75 (60)
92.4 (74) 1.3 (1) 6.3 (5)
92.4 (74) 1.3 (1) 6.3 (5)
91.3 (73) 1.3 (1) 1.3 (1) 1.3 (1) 1.3 (1) 3.8 (3)
92.5 (74) 2.5 (2) 0 (0) 0 (0) 2.5 (2) 2.5 (2)
55 (44) 10 (8) 26.3 (21) 20 (16) 0 (0) 3.8 (3) 1.3 (1) 1.3 (1) 8.8 (7)
42.5 (34) 2.5 (2) 40 (32) 6.3 (5) 6.3 (5) 5 (4) 5 (4) 0 (0) 8.8 (7)
0 (0) 42.5 (34) 57.5 (46)
17.5 (14) 30 (24) 52.5 (42)
38.8 (31) 21.3 (17) 7.5 (6) 7.5 (6) 8.8 (7) 8.8 (7) 7.5 (6)
28.7 (23) 27.5 (22) 11.3 (9) 13.8 (11) 10 (8) 7.5 (6) 1.3 (1)
⁎ Participants were allowed to endorse more than one occupation.
specified that the issues should be specific and framed respectfully (inspired from Van den Broucke, Vandereycken, & Vertommen, 1995). Partners were then brought into the same room and instructed to discuss these issues for 15 min. They were told that both of them must address at least one point on their list, and to continue discussing even if they talked about every point; they were free to generate new ideas as long as they remained within the suggested theme. To reproduce as much as possible a real-life couple discussion, no other rule was given for the discussion, each partner was free to talk as much points and as much long as he or she wanted. Discussions were videotaped to ensure that all participants adhered to the instructions. After the discussion, the partners were separated and asked to rate their mood again. They were also asked to assess their appetite perceptions. Next, a bogus taste test was introduced. As participants were recruited to take part in a study examining the impact of stress on food taste, they ignored that the amount of food eaten would be measured. Pre-weighed food was presented uniformly to participants and they were told to taste at least one bite of each food item in order to complete the taste test (see Section 2.3.4. Bogus taste test). They were told to eat as much as they wanted since the food was prepared just for them. Participants were alone in the room while completing the 10-min taste test. Afterwards, the leftover food was weighed using the same calibrated scale. Participants were then instructed to complete the questionnaires. Finally, both partners were brought together for the debriefing session. They were probed for suspicions about the true purpose of the experiment; none guessed that the amount of food eaten was measured. A second informed consent was signed. Objective measures of height and weight were taken.
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2.3. Measures 2.3.1. Mood Participants' mood was assessed before and after the discussion with the following statement: “Altogether my mood at the moment is…” on a 150 mm VAS on which the end points were labeled “very good” and “very bad” (based on Dingemans, Martijn, Jansen, & van Furth, 2009). Mood change was calculated by subtracting the mood evaluation before the discussion from the mood evaluation after the discussion. 2.3.2. Appetite perceptions Appetite was evaluated with four 150 mm VAS: desire to eat, hunger, fullness, and prospective food consumption (Hill & Blundell, 1986). For example, hunger was evaluated with the question: “How hungry do you feel?” The end points were labeled “Not hungry at all” and “Very hungry”. A total appetite perceptions score was obtained by calculating the mean of four items (reversed score for fullness). 2.3.3. Restrained eating Restrained eating was measured by the Revised Restraint Scale (Herman & Polivy, 1980). This 10-item scale measures restrained eating and has two subscales: concern for dieting and weight fluctuation. It has good psychometric properties (Laessle, Tuschl, Kotthaus, & Pirke, 1989). The Cronbach's alpha in the present study was 0.78, which is sufficient. 2.3.4. Bogus taste test All participants were presented with four bowls containing 200 g of milk chocolate M&M, 60 g of classic Lay's chips, 120 g of Teddy Graham vanilla cookies, and 100 g of house brand salted pretzels. All food items were removed from their original packaging, and uniformly presented in four separate clear bowls placed on a plastic tray. Participants were asked to taste and rate each food using VAS (e.g., To what extent is it salty?). Total food intake in grams was determined by subtracting the weight of the leftover food from the pre-weighed food for each food item and then calculating the sum of those differences.3 2.3.5. BMI Participants' height and weight were measured and BMI (kg/m2) was calculated. 2.4. Statistical analysis Analyses were carried out using SPSS version 20.0. A manipulation check for mood change was performed using a 2 (time) × 2 (sex) repeated-measures analysis of variance. A multivariate analysis of variance (MANOVA) was performed to examine mean differences among women and men with respect to food intake, restraint score (RS), BMI, and appetite. In order to test the moderating effect of BMI and RS on the relationship between food intake and mood change, multiple regression analyses with three-way interactions were performed separately for men and women using model three of the PROCESS macro developed by Hayes (2013). PROCESS calculates all the necessary products, estimates the best-fitting ordinary least squares regression model, and tests the three-way interaction (Hayes, 2013). A significant moderated moderation effect would be demonstrated by a significant three-way interaction, regardless if there was or was not a main effect for the independent variable (mood change) or the moderator variables (BMI and RS). In the case of a significant interaction, PROCESS would produce the simple slopes at −1, 0, and 1 standard deviation (SD) of the moderators (BMI and RS) when estimating the conditional effect (CE) of the 3 Total caloric intake was also calculated, and was highly correlated with intake in grams (r = 0.997; n = 160). Thereby, food intake was reported in grams in the following analyses.
independent variable (mood change) on dependent variable (food intake). Prior to analyses, variables were z-standardized, and correlations between food intake and potential covariates (appetite perceptions and relationship duration) were tested. Furthermore, the dependent variable (food intake) was inspected for outliers. All values located above the 97th percentile of the distribution (n = 4) were winsorized to bring them to the 97th percentile. All independent variables were screened for potential multivariate outliers. Two cases among women and three among men were identified through Mahalanobis distance as multivariate outliers (p b 0.001). Since there was no difference in the pattern of results among men when the three outliers were included, the analyses will include the outliers to maximize statistical power. In contrast, the two outliers changed the pattern of results for women and thus were not included in the analyses. Also, two additional participants were dropped from analyses because of missing data. The analysed sample consisted of 79 men and 77 women. 3. Results 3.1. Manipulation check of mood The manipulation check yielded a significant time by sex interaction, F(1, 78) = 6.46, p = 0.013, η2 = 0.076. Although men experienced a worsening of mood (before the discussion: M = 3.25, SD = 2.92; after the discussion: M = 3.46, SD = 2.89), post-hoc pairwise comparisons indicated that the effect of time, i.e., mood change, was significant only among women, F(1, 78) = 15.92, p b 0.001 (before the discussion: M = 2.71, SD = 2.52; after the discussion: M = 3.84, SD = 2.99). 3.2. Sex differences Results of the MANOVA revealed a significant multivariate effect indicating a significant sex difference, Wilks' λ = 0.662, F(5, 150) = 15.31, p b 0.001. Given the significance of the overall test, the univariate main effects were examined. They yielded a significant sex difference for food intake, F(1, 150) = 16.48, p b 0.001, and RS F(1, 150) = 16.07, p b 0.001. Men ate significantly more than women (respectively, M = 83.78, SD = 36.39; M = 61.86, SD = 30.72), while women reported significantly higher RS than men (respectively, M = 13.06, SD = 5.07; M = 9.68, SD = 5.45). No difference was noted for BMI and appetite perceptions. 3.3. Relationship between mood change and food intake Since appetite perceptions was significantly correlated with food intake among men and women (respectively, r = 0.461, p b 0.001; r = 0.283, p = 0.012), it was entered in the equation as a covariate. Relationship duration was not correlated with women's food intake, but was significantly correlated with men's food intake. It was not included as a covariate in the final model since it did not significantly add to the model. Among women, the overall multiple linear regression model was significant and accounted for 30% of the variance in food intake, R2 = 0.30, F(8, 68) = 3.61, p = 0.002. Table 2 shows that the three-way interaction between mood change, BMI and RS was a significant predictor of food intake. That is, BMI moderated the effect of mood change on food intake while RS moderated the moderating effect of BMI. Fig. 1 illustrates the three-way interaction. Examination of the interaction indicated that women who presented both high RS and high BMI (one SD above the mean) ate significantly more when their mood worsened (CE = 0.4348, p = 0.02). For all other women, there was no significant effect of mood change on food intake, with non-significant CEs of BMI and RS (all p N 0.05). The Johnson-Neyman technique (Johnson & Neyman, 1936) was used to determine the value of RS at which the interaction became significant. At
M. Côté et al. / Eating Behaviors 23 (2016) 86–90 Table 2 Multiple regression models predicting the effect of mood change on food intake in women and men.
Women
Men
Predictors
β
t VALUE
p
Mood BMI RS Mood × BMI Mood × RS BMI × RS Mood × BMI × RS Appetite† Mood BMI RS Mood × BMI Mood × RS BMI × RS Mood × BMI × RS Appetite†
−0.0597 −0.0191 0.2181 0.2833 −0.0318 0.1947 0.3643 0.3305 0.1567 0.0068 0.1690 −0.0494 −0.0240 0.1168 0.0047 0.1408
−0.3997 −0.1047 1.5166 1.1600 −0.1818 1.6844 2.1399 3.0948 1.4300 0.0540 1.2418 −0.2592 −0.1406 1.0332 0.0289 4.8507
0.6907 0.9169 0.1340 0.2501 0.8563 0.0967 0.0360⁎ 0.0029⁎⁎ 0.1572 0.9571 0.2184 0.7963 0.8886 0.3051 0.9770 0.0000⁎⁎⁎
Note: Women: n = 77; Men: n = 79. ⁎ p b 0.05 ⁎⁎ p b 0.01 ⁎⁎⁎ p b 0.001. † Covariate.
the 0.05 alpha level, women with a RS of 15.51 or higher ate significantly more as their mood worsened, which is consistent with the existing literature which propose a cut-off score of 15 or more to classify restrained eaters (Goldman, Herman, & Polivy, 1991; Polivy, Herman, & Deo, 2010). Among men, the overall multiple linear regression model was also significant and accounted for 31% of the variance in food intake, R2 = 0.31, F(8, 70) = 3.99, p = 0.001. There was no significant main effect of mood change on food intake, nor any significant interaction (Table 2). Only appetite perceptions was found to be a significant predictor of food intake in men (p b 0.001). 4. Discussion The aim of the present study was to investigate the impact of an experimental negative mood induction, in the form of a stressful couple discussion, on food intake in both partners, while taking into account the possible moderating effects of BMI and restraint. The initial hypothesis concerning the simultaneous moderating effects of BMI and restraint on the relationship between mood change and food intake was confirmed among women. More specifically, the mood worsening induced by the stressful couple discussion led to an increase in food intake 1.5
RS=-1, BMI=-1 RS=1, BMI=-1
RS=-1, BMI=1 RS=1, BMI=1
1 y = 0,4349x + 0,3723*
Food intake
0.5 y = 0.0375x - 0.0182 0 y = -0.0856x - 0.3786
-0.5
y = -0.708x + 0.0561 -1 -1.5 -2
Low mood change
High mood change
Fig. 1. Interaction plot showing associations between subjective mood change and food intake for women at different values of restraint as measured by the Restraint Scale score and body mass index (BMI). All variables are z-standardized. 1: One standard deviation above the mean; −1: One standard deviation under the mean.
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only among restrained women with a high BMI. The observation of the simultaneous effect of BMI and restraint on measured food intake following an induced negative mood is an important contribution of the present study. To our knowledge, no other study on stress-induced eating has examined their concomitant effect on food intake. Results support previous studies showing that overweight women (Lemmens et al., 2011; Slochower et al., 1981) and women with high scores on the Restraint Scale (Cools et al., 1992; Schotte et al., 1990; Tanofsky-Kraff, Wilfley, & Spurrell, 2000) are more prone to disinhibited eating when facing stress and negative emotion. However, in the present study, neither restrained eating nor BMI alone accounted for the association between mood and food intake. It was rather the interaction between both high restraint and high BMI that predicted women's greater food intake following their negative mood change. One possible explanation for the complex relationship observed herein is the inclusion of women from the general population. Indeed, about the half of our sample consisted of people from the general population (the other half consisted of student), whereas most stress-induced eating studies use samples comprised uniquely of female college students (e.g., Cools et al., 1992; Schotte et al., 1990; Tanofsky-Kraff et al., 2000). In fact, the relationship between weight and restrained eating observed among the general population differs from what is observed among college students. For example, in our sample, 67% of overweight/obese women were restrained eaters compared to 18% of normal-weight women. In female college students, only 33% of overweight/obese students were identified as restrained eaters compared to 50% of normalweight students (Rand & Kuldau, 1991). It might be that as women get older, restraint is more tightly linked to overweight and obesity, explaining the observed interaction effect. Longitudinal studies have shown that, in the long term, unsuccessful restrained eating is associated with an increase in BMI, especially among women (Drapeau et al., 2003; van Strien, Herman, & Verheijden, 2014). It is possible that overtime it becomes increasingly difficult for women to maintain strict dietary restraint, making them more prone to transgress their dietary rules, which could lead to weight gain (Polivy, 1996; van Strien et al., 2014). Sex comparisons showed that men and women react quite differently when facing a dyadic stressor. First, the mood of the women was more affected by the stressful couple discussion. These results are not surprising since women tend to show a greater physiological reaction to a stressful couple discussion than men (Kiecolt-Glaser & Newton, 2001). Second, food intake was not explained by the same variables for men and women. Indeed, even though men ate significantly more than women, the moderating effect of restraint and BMI on the relationship between mood change and food intake was not found among men. In fact, men ate mostly based on their appetite perceptions. These results are coherent with evidence showing that men have greater caloric needs (Kiefer, Rathmanner, & Kunze, 2005), and eat more intuitively, i.e., in response to hunger and satiety cues, than women (Denny, Loth, Eisenberg, & Neumark-Sztainer, 2013; Smith & Hawks, 2006). This specific sex difference can also be explained by the fact that men had significantly lower levels of restraint than women, as usually observed in other studies (Kiefer et al., 2005; Rand & Kuldau, 1991). Since men are known to be less preoccupied with their weight than women (Forrester-Knauss & Zemp Stutz, 2012; Rolls, Fedoroff, & Guthrie, 1991), it is not surprising that their food intake was determined by their appetite perceptions rather than by mood, especially since their mood did not significantly worsen following the stressful discussion. Although the findings of the present study propose significant contributions to the stress-induced eating literature, their limitations should be stated. First, in order to reproduce as close as possible the realism of a real-life couple discussion, no rule was given to participants about speaking turns during the discussion. The only aspect mentioned was that both partners had to address at least one aspect they would like their partner to change. Although this may contribute positively to the external validity of the study, it could be hypothesized that unequal talking turns could have influenced partners' mood (e.g., being
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mostly on the receiving end of the discussion could have been more stressful), which could explain the difference found between men and women regarding mood change following the discussion. Furthermore, for reasons of cost and achievability, self-reported mood VAS was used to measure stress. Physiological measures such as cortisol rates, blood pressure and heart rate would have been more objective ways to measure stress. Because physiological measures generally fall outside the scope of consciousness and are not impacted by social desirability, they may be more accurate to assess stress (Rutledge & Linden, 1998). 5. Conclusions To conclude, the findings of the present study support the complex relationship between stress and eating and provide a better understanding of the effect of gender, restraint and BMI on this relationship. A stressful couple discussion led restrained women with a high BMI to greater food intake. Considering that dyadic stress is part of everyday life for many couples, the results of the present study suggest that it is relevant to sensitize women struggling with weight issues about the potentially deleterious effect of a discrete episode of dyadic stress on their eating behaviors. Contributors All authors contributed to the design of the study. Author Côté wrote the protocol, conducted literature searches and statistical analysis, and wrote the first draft of the manuscript. All authors contributed to and have approved the final manuscript. Conflict of interest All authors declare that they have no conflicts of interest. Acknowledgments We thank Hélène Paradis for statistical analysis guidance, as well as Annette Gallant for language editing. We also thank the Centre de recherche interdisciplinaire sur les problèmes conjugaux et les agressions sexuelles (CRIPCAS) for funding support.
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