Research reportEmotional eating and Pavlovian learning: Does negative mood facilitate appetitive conditioning?☆
Introduction
Emotional eating (i.e., eating in response to negative emotions) is a contributing factor in obesity and eating disorders (Hays, Roberts, 2008, Polivy, Herman, 2002). Several studies have shown overeating after the experience of negative emotions, such as stress, anxiety or sadness, in dieters (Cools et al, 1992, Heatherton et al, 1991, Loxton et al, 2011, Wallis, Hetherington, 2004), obese people (Patel, Schlundt, 2001, Schneider et al, 2010), and obese binge eaters (Agras, Telch, 1998, Chua et al, 2004). However, it is unknown how emotional eating originates or how it is maintained.
It has been suggested that emotional eating is a learned behaviour, as the natural response for most people in the face of adversity is to decrease food intake (Wardle, 1990). Specifically, classical or Pavlovian conditioning has been proposed to be the involved mechanism (Greeno, Wing, 1994, Jansen, 1998, Jansen et al, 2011, Wardle, 1990). In classical conditioning, food intake is regarded as an unconditioned stimulus (US), eliciting unconditioned physiological responses (URs), such as insulin release, blood sugar increase and salivation. Over time, stimuli that are systematically paired with food intake can start to predict intake, thereby becoming conditioned stimuli (CS). After learning that the CS predicts the occurrence of the US, CSs are capable of eliciting appetitive responses, such as a conditioned desire to eat (i.e., cue reactivity). Virtually any stimulus in the environment can become a food-signalling CS, including the sight or smell of food, a certain time of the day, the environment or context (Jansen, 1998, Wardle, 1990) and it is also suggested that emotions can become food-signalling CSs (Jansen et al., 2011).
Experimental studies indeed show that eating desires can be conditioned quite easily. Van Gucht and colleagues (Van Gucht et al, 2013, Van Gucht et al, 2010, Van Gucht et al, 2008, Van Gucht et al, 2008) and Papachristou, Nederkoorn, Beunen, and Jansen (2013) convincingly demonstrated appetitive conditioning to a neutral cue (i.e., a serving tray) in several studies, with participants reporting increased food expectancy, eating desire, and automatic approach tendencies when presented with the cue that predicted the intake of appetizing foods (CS+; a tray in one shape and colour) compared to the cue that did not predict the intake of appetizing foods (CS−; a tray in another shape and colour). Van den Akker, Jansen, Frentz, and Havermans (2013) extended these findings by showing appetitive conditioning in response to contexts (neutral environments in a virtual reality lab), indicating that besides specific cues, specific contexts can also come to elicit food expectancy and eating desire after the context becomes a predictor of intake. In addition to expectancy and desire, Van den Akker et al. (2013) also measured salivation and actual food intake. They found increased saliva production in participants presented with the CS+, but not the CS− context. Thus, after only 6 pairings of a neutral context with the intake of appetizing food, some evidence was found that participants salivated more in the context that predicted the intake compared to a context that did not predict intake. The authors also found that food intake increased in the CS+ compared with the CS− contexts, but only for participants high in impulsivity. This effect of impulsive people showing increased conditioned food intake is interesting, considering the wealth of research showing a positive association between impulsivity on the one hand and food consumption and obesity on the other hand (see Guerrieri, Nederkoorn, & Jansen, 2008 for an overview; Velázquez-Sánchez et al., 2014). Importantly, a role for impulsivity in appetitive conditioning was proposed by Gray (Corr, Pickering, & Gray, 1995) in his BIS/BAS theory, which predicted that high impulsivity (i.e., strong BAS; Behavioural Approach System) is related to increased associative appetitive learning, while high anxiety (i.e., strong BIS; Behavioural Inhibition System) is related to increased aversive learning. Research with regard to the facilitating role of impulsivity in appetitive learning has however yielded mixed results (Corr, 2004, Corr et al, 1995, Paisey, Mangan, 1988, Papachristou et al, 2013, Van den Akker et al, 2013, Zinbarg, Mohlman, 1998, Zinbarg, Revelle, 1989) and studies specifically on food as the appetitive stimulus are scarce (Papachristou et al, 2013, Van den Akker et al, 2013).
If emotional eating is, as we suggest, learned through classical conditioning, two pathways through which this could occur are most obvious. First, it is frequently reported by emotional eaters that they overeat when feeling bad. If a particular emotional state is frequently associated with the intake of appetizing high calorie foods, and the contingency between this emotion and eating is strong (i.e., the probability of the emotion leading to eating approaches one), this association will ultimately lead to the emotion becoming a reliable predictor of food intake, i.e., a CS. After conditioning, confrontation with the CS (emotion) will elicit cue reactivity, i.e., an eating desire or food craving, and ultimately food intake. An alternative pathway is negative mood facilitating the learning of associations between neutral stimuli and food intake. High-calorie foods have strong rewarding properties (see for example Coletta et al, 2009, Macht, Dettmer, 2006, Macht, Mueller, 2007, Small et al, 2001), which might be extra rewarding and thus relevant for people who find themselves in a negative emotional state (Baker et al, 2004, Hepworth et al, 2010). They would benefit from learning that certain cues predict food intake that might alleviate their bad mood. In this model, a neutral stimulus from the environment, or the environment itself, becomes the CS. The CS predicts food intake and as a consequence of the rewarding foods, a better mood. This pattern might be considered a specific form of state-dependent learning or context learning, in which the negative mood functions as a state or context. Furthermore, research in fear conditioning has brought forward some evidence that negative contexts (i.e., threat) facilitate conditioning (Karos, Meulders, & Vlaeyen, 2014). The latter pathway is the one under investigation in the current study.
In the present study, we tested the hypothesis that participants in a negative mood would show facilitated appetitive conditioning. We expected stronger differential responses to the CSs for the group that was conditioned in a negative mood compared to the group that was conditioned in a neutral mood: those in a negative mood would show a larger difference in expectancies to receive food, desires to eat food, saliva production, and food intake in response to the CS predicting the intake of high-caloric food (CS+) than to the CS not predicting food intake (CS−). Because impulsivity is strongly related to overeating and obesity and earlier research shows that highly impulsive participants in particular eat more after classical conditioning (Van den Akker et al., 2013), we investigated the possibility of a moderating effect of impulsivity on expectancy, desire, salivation and food intake, with higher levels of impulsivity facilitating conditioning.
Section snippets
Participants
A total of 127 female undergraduate students, aged between 17 and 30 years (M = 19.98, SD = 1.79), took part in the study. The students were told that the study concerned examining the relationship between music and taste. To be included, participants had to like chocolate mousse (the food of choice in the current study; scoring at least 3 on a 5-point Likert scale ranging from ‘I do not like chocolate mousse at all’ (1) to ‘I really like chocolate mousse’ (5)), which was assessed with a single
Group characteristics
As shown in Table 1, the participants in the four conditions did not differ on age, BMI, BIS-11 scores, DEBQ emotional eating, DEBQ dietary restraint, baseline mood (i.e., happiness and sadness), minutes since last eaten, or baseline hunger. However, a difference in hunger did emerge after the mood manipulation. Direct comparison between hunger and desire to eat in the negative and neutral mood conditions yielded significant differences, F(1, 119) = 14.10, p < .001 and F(1, 119) = 30.87, p
Discussion
In the current study we took a first step in shedding light on the origin of emotional eating by testing whether classical conditioning processes might be involved. More specifically, we investigated whether being in a negative mood facilitates appetitive conditioning, as measured by the expectancy to eat, desire to eat, saliva production and food intake. The results indicate that the conditioning procedure in itself was successful; that is, differential acquisition of eating expectancy was
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2018, Journal of Behavior Therapy and Experimental PsychiatryCitation Excerpt :Models of overeating state that food cue reactivity can be acquired through classical conditioning (A. Jansen, 1998): by associating food intake (unconditioned stimulus; US) with predictive cues (conditioned stimulus; CS), such as the smell and sight of food, presentations of merely the CS are capable of inducing cue reactivity (conditioned response). Results of human laboratory studies confirm that associations between food intake (US) and neutral stimuli (CS) are easily learned (Bongers, van den Akker, Havermans, & Jansen, 2015; van den Akker, Havermans, Bouton, & Jansen, 2014). If CS-US associations are acquired in daily life through classical conditioning, extinction of food cue reactivity, by repeated exposure to CSs without the US (eating), could be helpful to reduce overeating.
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Acknowledgements: This study is part of an ongoing project that is financed by the Netherlands Organisation for Scientific Research (NWO): Vici Grant 453.10.006, awarded to Anita Jansen.