Effects of food preparation on liking

Running head: Does self-prepared food taste better?

Does self-prepared food taste better? Effects of food preparation on liking

Simone Dohle Social Cognition Center Cologne, University of Cologne

Sina Rall and Michael Siegrist ETH Zurich

Author Note E-mail addresses: [email protected] (S. Dohle); [email protected] (S. Rall); [email protected] (M. Siegrist). Correspondence concerning this article should be addressed to: Simone Dohle, Social Cognition Center Cologne, University of Cologne, University of Cologne, Richard-Strauss-Str. 2, 50931 Cologne, Germany. E-mail: [email protected].

Abstract Objective: The aim was to examine whether self-preparation of food increases the liking of healthy and unhealthy foods. Method: The study used a 2 (preparation: self-prepared vs. otherprepared) × 2 (healthiness: healthy vs. unhealthy) between-subject design. Female participants (N = 120) tasted food that was either self-prepared or other-prepared, and that either contained markedly healthy or unhealthy ingredients. Interindividual differences in dietary restraint were also assessed. Liking and perceived healthiness of the food served as the main dependent variables. Results: A significant interaction effect of food preparation and healthiness of the food on liking was revealed: Self-preparation increased the liking of the healthy but not of the unhealthy food. This effect was particularly strong for individuals with high levels of dietary restraint. Moreover, the combined effect of food preparation and healthiness of the food on liking was mediated by perceived healthiness of the food. Conclusion: The results bolster public health programs trying to encourage people to eat less prepared, ready-to-eat foods and more selfprepared food. Because time available for home food preparation is often limited, programmatic efforts to encourage food preparation could be extended to schools and workplaces.

Keywords: food preparation; cooking; IKEA effect; liking; fast food; obesity

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Does self-prepared food taste better? Effects of food preparation on liking In many countries, the overall amount of time spent in food preparation has decreased over the past decades. Between 1975 and 2006, the time American women typically spent in food preparation declined from 92 to 51 minutes per day; for men, time spent in these activities remained stable and at less than 20 min per day (Zick & Stevens, 2010). Alongside with this development, an increase in the consumption of prepared, ready-to-eat meals and awayfrom-home-foods, particularly fast foods, has been documented (Monsivais, Aggarwal, & Drewnowski, 2014; Smith, Ng, & Popkin, 2013). Numerous studies have linked these changes in food preparation patterns to an increased risk of weight gain, overweight, and obesity (Appelhans et al., 2012; Bowman, Gortmaker, Ebbeling, Pereira, & Ludwig, 2004; Bowman & Vinyard, 2004; Chan & Sobal, 2011; Larson, Neumark-Sztainer, Laska, & Story, 2011; Paeratakul, Ferdinand, Champagne, Ryan, & Bray, 2003). Frequent use of fast-food restaurants is related to higher intake of total energy, sugarsweetened beverages, and fat (Appelhans et al., 2012; Bowman et al., 2004; Bowman & Vinyard, 2004; Larson et al., 2011; Paeratakul et al., 2003). In addition, fast food consumption and awayfrom-home eating is directly associated with higher body weight and risk of obesity (Bowman & Vinyard, 2004; Chan & Sobal, 2011; Larson et al., 2011). In contrast, involvement in the preparation of food and higher cooking skills are related to increased intakes of fruits, vegetables, and whole grains (Chu, Storey, & Veugelers, 2014; Hartmann, Dohle, & Siegrist, 2013; Larson, Perry, Story, & Neumark-Sztainer, 2006; McLaughlin, Tarasuk, & Kreiger, 2003; Monsivais et al., 2014), and frequent meal planning and cooking are important for successful weight loss maintenance (Kruger, Blanck, & Gillespie, 2006).

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As a consequence of these findings, health authorities in many Western countries have invested in public health programs to reduce fast food consumption and to promote food preparation and cooking at home (Kumanyika et al., 2002; Lichtenstein & Ludwig, 2010; Nestle, 2010; Smith et al., 2013). However, most of these recommendation are based on correlational, cross-sectional studies or on overall evaluations of multicomponent interventions (Reicks, Trofholz, Stang, & Laska, 2014; van der Horst, Ferrage, & Rytz, 2014), but to give evidencebased recommendations concerning food preparation, experimental studies are needed. Until now, experimental research on food preparation has been surprisingly limited (Dohle, Rall, & Siegrist, 2014; van der Horst et al., 2014), although such studies could also shed more light on the question why and under what conditions food preparation might lead to increase liking of foods or better food-related choices. One of the few studies that used an experimental approach to food preparation focused on the mere act of preparing foods (Dohle et al., 2014). In this study, participants tasted a 444 kcal raspberry milkshake that was either selfprepared or other-prepared, i.e., prepared by the experimenter shortly before the participants arrived in the experimental room. In both experimental conditions, participants read the recipe that consisted of an ingredient list and the steps of preparation. In a subsequent taste test, the self-prepared milkshake received higher liking ratings than the other-prepared milkshake. In addition, participants who prepared the milkshake themselves consumed a larger quantity of the shake. Results of this study are in line with the so-called “IKEA effect”, i.e. the finding that people like and overvalue objects that they have created themselves, like IKEA boxes, folded

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origami, or built sets of Legos (Norton, Mochon, & Ariely, 2012)1. The IKEA effect might be best explained —in terms of cognitive dissonance—as effort justification (Aronson & Mills, 1959; Festinger, 1957). According to this, people like self-made objects more than objects that were created by someone else because they have put more effort in these self-made objects. In addition, these efforts feel rewarding, because self-created products also signal competence to the self and others (Mochon, Norton, & Ariely, 2012). The same principle might apply in the case of self-prepared food: Because people put time and effort in food preparation, they like self-made foods more than those foods that are ready-to-eat (Dohle et al., 2014). In the case of food preparation, however, self-preparation might also lead to the effect that people become more aware about the ingredients that constitute a food, because they look at, handle, and often measure the ingredients. Thus, food preparation may increase the ‘health salience’ of a food, which can be defined as a higher awareness that the ingredients of a food are healthy or unhealthy. Higher health salience may affect the liking of the food as well, especially if a person cares about healthy eating. This additional health-salience effect of food preparation is probably masked in Dohle et al.’s (2014) study, because the milkshake that had to be prepared contained ingredients that could be considered as unhealthy (e.g. cream) and healthy (e.g. raspberries). Thus, the milkshake was neither prototypically healthy nor unhealthy. It remains unclear if an increase in liking for self-prepared foods will still

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The IKEA effect is similar but not identical to the well-researched endowment effect (Kahneman, Knetsch, &

Thaler, 1990; Thaler, 1980). While research related to the endowment effect shows that that mere ownership of a product increases its value, the IKEA effect is demonstrated when invested labor leads to increased product valuation (Norton et al., 2012). The two effects, however, might work side by side and reinforce each other in real life situation (Hattie & Yates, 2014).

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be found for different types of foods that differ more distinctly in regard their healthiness. For markedly unhealthy foods, a higher health salience due to food preparation may decrease the liking of the food, and thus, may countervail the increases in liking that occur because of effort justification. The aim of the present study was to examine if self-preparation leads to an increase in liking for different types of foods. From a public health perspective, it is important to explore if food-preparation can increase the liking of healthy and unhealthy foods. Fruit and vegetable liking and consumption are usually low in children and adults (Bucher, Siegrist, & van der Horst, 2014; Cooke & Wardle, 2005), although a diet rich in fruit and vegetables has been shown to reduce the risk of cancer and cardiovascular diseases (Bazzano et al., 2002; Block, Patterson, & Subar, 1992) and may reduce long-term risk of obesity and weight gain (He et al., 2004). Finding ways to increase fruit and vegetable consumption would therefore be important for public health; on the other hand, an intervention that increases the liking of healthy foods and unhealthy foods at the same time might be critical and jeopardize positive health outcomes. In this study, we hypothesized that for healthy foods, food preparation will lead to an increase in liking. This increase in liking should occur because of effort justification, but also because of an increase in health salience (higher awareness that the ingredients are healthy). For unhealthy foods, however, no increase of liking should occur: Although people also need to justify the effort for preparing an unhealthy food, higher health salience (in this case, higher awareness of the unhealthy ingredients) should countervail the effect of effort justification. Based on the previous line of reasoning regarding the underlying process of this effect, we also assumed that the combination of food preparation and the confrontation with healthy (unhealthy) foods will increase (decrease) the perceived healthiness of the food, which in turn 6

will lead to higher (lower) liking; thus, the combined effect of food-preparation and healthiness of food on liking will be mediated by the perceived healthiness of the shake. Beyond doubt, however, healthy eating and low-calorie diets are more important for some people than for others. Especially people high in dietary restraint, i.e., individuals who intentionally restrict their caloric intake for the purpose of weight loss or weight maintenance (Herman & Mack, 1975), might be more concerned about foods and their ingredients (de Ridder, Adriaanse, Evers, & Verhoeven, 2014; de Witt Huberts, Evers, & de Ridder, 2013), and recent research also suggests that restrained eating is not only driven by weight concerns, but also by health considerations (Keller & van der Horst, 2013). Because it is likely that high-restrained eaters care more about the healthiness of a food, we also tested the hypothesis that the combined effect of food-preparation and healthiness of food on liking is more pronounced among (or only holds for) people with higher degrees of dietary restraint. Thus, we employ what Spencer, Zanna, and Fong (2005) have termed a moderation-of-process design, which can provide compelling— and in this case, additional—evidence of a proposed psychological process.

Method Participants and design Participants were 120 female volunteers who were recruited via a web-based online recruitment system at the University of Zurich. Mean age of the sample was M = 26.07 (SD = 5.74), and most of them (93%) were students2. Participants received financial compensation for

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According of the Swiss Federal Statistical Office (BFS), the average age of students in Switzerland is M = 26.49

years (BFS, 2013); thus, our sample was not older that the average student population in Switzerland.

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participation (CHF 10). Sample size was determined a priori using G*Power 3 (Faul, Erdfelder, Lang, & Buchner, 2007) based on an effect size of f = 0.26 (Dohle et al., 2014) resulting in a required total sample size of 119 participants to detect main and interaction effects with α = .05 and power = .80. The study included females only in order to maximize variability in dietary restraint. The study employed a 2 (preparation: self-prepared vs. other-prepared) x 2 (healthiness: healthy vs. unhealthy) between-subject design. Liking and perceived healthiness of the milkshake served as the main dependent variables. Additional analyses also examined if food preparation also influenced estimations of the caloric content of the shake and the amount consumed.

Material and Procedure All participants were tested individually in the same experimental room. Upon arrival, participants were greeted by the experimenter and were told that they were participating in a taste test. Written informed consent was obtained from all participants. They were randomly assigned to the experimental conditions. Preparation manipulation. In the self-prepared condition, participants were first presented the recipe for the milkshake, which consisted of an ingredient list and the steps of preparation (note that no nutritional or caloric information was given). All ingredients and kitchen utensils, including a hand-held blender, a scale, and a measuring cup, were provided at a table. Participants were asked to prepare the milkshake according to the recipe; they measured the ingredients, blended them, and filled the prepared shake into a transparent cup. Unbeknownst to the participants, the experimenter also weighed the cup. Participants were then seated at another table, where they proceeded with the ostensible taste test. In the other-prepared 8

condition, the experimenter prepared and weighed the milkshake shortly before participants’ arrival. Participants were seated at a table and confronted with the ready-to-drink milkshake and the recipe. The recipe was presented for one minute; then, the ostensible taste test started. Healthiness manipulation. Healthiness was manipulated by presenting participants either a (low-calorie) raspberry milkshake or a (high-calorie) chocolate milkshake. The raspberry milkshake contained 100g of raspberries, 150ml of milk (2.5% fat), and 10g of sugar (in sum, 189 kcal). The chocolate milkshake contained 200ml of chocolate ice cream, 50ml of milk (3.5% fat), and 50ml of cream (in sum, 499 kcal). Selection of ingredients was based on prior research showing a tendency for people to dichotomize foods into those good for one's health and those bad for one's health (Rozin, Ashmore, & Markwith, 1996). According to this, healthy foods are thought to be inherently low in calories and complete in nutrients, while unhealthy foods are thought to be high in calories and low in nutrients (Rozin et al., 1996). In particular, many people regard fruits as healthy and chocolate as unhealthy (Bucher, van der Horst, & Siegrist, 2013; Chernev, 2011; Rozin et al., 1996). In addition, a sweet (instead of a savory) shake in the healthy condition was chosen to minimize the confounding effect of basic taste. A shake was deemed ideal to measure consumption, which was easier to realize with a liquid food. In all conditions, participants were informed that they could taste as much from the shake as they wanted, but that they were not allowed to take the milkshake with them when the study was completed. During the taste test, participants were asked to fill in a questionnaire; they indicated how much they liked the milkshake, how healthy and calorie-rich they perceived the shake to be, filled in some filler questions that were related to the ostensible taste test, indicated how hungry they were when they tried the shake, completed the dietary restraint scale, and were asked about their height and weight. The dietary restraint scale was administered at the end of 9

the taste test in order not to sensitize participants to their eating behavior by presenting the restraint scale beforehand (Hofmann, Rauch, & Gawronski, 2007; Polivy & Herman, 1976). At the end of the study, the cups were removed and weighed. All participants were informed about the study’s aim subsequent to the study’s completion.

Measures Liking. The first question in the questionnaire asked for liking of the milkshake. Ratings for liking were given on a 100-mm visual analogue scale (VAS) that was anchored with the statements do not like at all and like very much. Perceived healthiness. Participants rated the perceived healthiness of the shake on a 100mm VAS that was anchored with the statements not at all healthy and very healthy. Calorie Content. In line with Dohle et al.’s (2014) study, in which participants were asked for calorie estimations but not about perceived healthiness, we also measured the estimated calorie content of the shake. To measure participants’ estimates of the milkshake’s energy content, they were asked to judge the shake on a 9-point Likert-scale ranging from no calories (1) to many calories (9). Hunger. Participants rated how hungry they were at the moment when they tried the milkshake; answers were given on a 9-point Likert-scale ranging from not at all hungry (1) to very hungry (9). Dietary restraint. The Revised Restraint Scale (Herman & Polivy, 1980) consists of two subscales: concern for dieting (RS-CD) and weight fluctuations (RS-WF; Dinkel, Berth, Exner, Rief, & Balck, 2005). However, it has been suggested to disregard RS-WF due to confounding with BMI and overweight and its lower internal consistency (Meule, Lutz, Vögele, & Kübler, 10

2012; Stroebe, 2008). Therefore, we only used RS-CD. For each person, a sum score based on the six items was calculated (M = 6.99, SD = 3.12; range: 1-16; α = .72); higher values indicate higher dietary restraint. The sum score of the RS-CD was slightly higher compared to those of female students of a German university in a validation study conducted by Dinkel and colleagues (2005). Body Mass Index (BMI). BMI was calculated by dividing weight (kg) by height2 (m2). Mean BMI in this sample was 21.65 (SD = 3.31). Consumption. Milkshake consumption was determined by subtracting the amount left of the preconsumption weight (measured in grams).

Results First, a 2 (preparation: self-prepared vs. other-prepared) x 2 (healthiness: healthy vs. unhealthy) analysis of variance (ANOVA) on liking was carried out. The main effect for preparation and the main effect for healthiness were not statistically significant, both p > .250. However, as predicted, the analysis yielded a significant interaction effect between preparation and healthiness, F(1, 116) = 6.93, p = .010, ηp2 = .06. A test of the simple effects revealed that in the healthy condition, participants liked the self-prepared milkshake more (M = 86.30, SD = 12.26) than the other-prepared milkshake (M = 76.80, SD = 20.84; F(1, 116) = 4.07, p = .046, ηp2 = .03). This pattern of results was reversed in the unhealthy condition: as a tendency, participants liked the other-prepared milkshake more (M = 83.83, SD = 16.52) than the selfprepared milkshake (M = 75.80, SD = 21.94); however, the simple effect was only marginally significant, F(1, 116) = 2.91, p = .091, ηp2 = .02. The interaction effect of preparation and healthiness on liking is depicted in Figure 1. 11

—Insert Figure 1 here— As expected, a 2 (preparation: self-prepared vs. other-prepared) x 2 (healthiness: healthy vs. unhealthy) ANOVA on perceived healthiness of the shake indicated a main effect of healthiness, indicating that the experimental manipulation was successful, F(1, 116) = 113.33, p < .001, ηp2 = .49. No main effect for preparation was found, p > .250. Moreover, there was also a significant interaction between preparation and healthiness, F(1, 116) = 11.33, p = .001, ηp2 = .09. In the healthy condition, participants perceived the self-prepared milkshake as healthier (M = 74.10, SD = 17.32) than the other-prepared milkshake (M = 59.57, SD = 19.51; F(1, 116) = 8.17, p = .005, ηp2 = .07). In the unhealthy condition, however, participants tended to perceive the other-prepared milkshake as healthier (M = 33.40, SD = 23.28) than the self-prepared milkshake (M = 23.73, SD = 18.11); however, the simple effect only approached significance, F(1, 116) = 3.62, p = .060, ηp2 = .03. The interaction effect of preparation and healthiness on perceived healthiness is also shown in Figure 1. To analyze in more detail whether perceived healthiness mediates the relationship between the interaction of food-preparation and healthiness of the food on liking, we conducted a mediated moderation multiple regression analysis as outlined by Muller, Judd, and Yzerbyt (2005). The mediation analysis is displayed in Table 1. The data show that perceived healthiness mediates the moderated effect of preparation and healthiness of the food, because (a) the preparation × healthiness interaction predicts the dependent variable, i.e, liking (see ANOVA results above and Table 1, column 1); (b) the preparation × healthiness interaction predicts the mediating variable, i.e, perceived healthiness (see ANOVA results above and Table 1, column 2); (c) the mediating variable predicts the dependent variable, i.e, liking (see Table 1, column 3);

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and (d) the effect of the preparation × healthiness interaction is only marginally statistically significant when the mediator is entered into the equation (see Table 1, column 1 vs. 3). To investigate the hypothesis that dietary restraint moderates the interaction between selfpreparation and the healthiness of foods on liking, a multiple regression analysis was conducted. Liking served as the dependent variable, and the dummy coded preparation (0 = other-prepared, 1= self-prepared) and healthiness (0 = unhealthy, 1= healthy) conditions, the dietary restraint scale (which was mean-centered and treated as a continuous variable), all possible two-way interactions, as well as the three-way interaction were entered as independent variables. This analysis revealed a significant interaction between the preparation and healthiness condition, b = 16.50, t = 2.49, p = .014, and between healthiness and dietary restraint, b = -3.32, t = -2.39, p = .018. These two-way interactions were qualified by a marginally significant three-way interaction, b = 4.31, t = 1.96, p = .053, as depicted in Figure 2. To decompose the three-way interaction, Hayes’s (2013) PROCESS macro was used. The preparation × healthiness interaction was examined separately for those who were relatively low in dietary restraint (−1 SD) and those who were relatively high in dietary restraint (+1 SD). This analysis indicated that the preparation × healthiness interaction was significant for those relatively high in dietary restraint (+1 SD), b = 29.94, t =3.09, p = .003, but not for those relatively low in dietary restraint (−1 SD), b = 3.07, t = 0.33, p > .250. Therefore, this two-way interaction of preparation × healthiness was decomposed for those who were relatively high in dietary restraint. —Insert Figure 2 here— Among those relatively high in dietary restraint, simple effects indicated that preparation was a significant predictor for liking in the healthy condition, b = 18.79, t = 2.94, p = .004. That is, high-restraint participants who prepared the milkshake themselves liked it more when it was a 13

healthy milkshake. However, no effect of preparation was found in the unhealthy condition, b = 11.15, t = -1.53, p = .130. Thus, when the milkshake was unhealthy, high-restraint participants’ liking was not dependent on whether they prepared the milkshake themselves or whether the experimenter prepared it. These analyses confirmed that dietary restraint moderates the interaction between self-preparation and the healthiness of food on liking. Additionally, we also analyzed if the experimental manipulations had an influence on the estimated caloric content and the amount of shake consumed. Concerning the estimated caloric content, a 2 (preparation: self-prepared vs. other-prepared) x 2 (healthiness: healthy vs. unhealthy) ANOVA showed a main effect for the healthiness of the shake, F(1, 116) = 70.80, p < .001, ηp2 = .38, but no main effect for preparation, p > .250. The analysis also yielded a significant interaction effect between preparation and healthiness on estimated caloric content, F(1, 116) = 5.92, p = .016, ηp2 = .05; this result is also demonstrated in Figure 1. Analyses of the simple effects indicated that in the healthy condition, participants estimated that the self-prepared milkshake contained less calories (M = 4.73, SD = 1.14) than the other-prepared milkshake (M = 5.50, SD = 1.70; F(1, 116) = 5.12, p = .026, ηp2 = .04). In the unhealthy condition, however, there was no statistically significant difference between the self-prepared (M = 7.33, SD = 1.09) and the other-prepared condition (M = 6.93, SD = 1.23; p = .240). In addition, there was no indication that the estimated caloric content mediated relationship between the interaction of food-preparation and healthiness of the food on liking. A mediated moderation multiple regression analysis (see above) revealed that the estimated caloric content was not related to the dependent variable (p > .250), and the preparation × healthiness interaction was still statistically significant when the mediator was entered into the analysis (p =.007).

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Concerning consumption, the 2 x 2 ANOVA revealed a main effect for the healthiness of the shake, F(1, 116) = 8.08, p = .005, ηp2 = .07. In general, participants consumed more of the healthy (M = 149.47, SD = 89.18) than of the unhealthy milkshake (M = 108.73, SD = 66.30), as shown in Figure 1. Neither a significant main effect for preparation (p > .250) nor an interaction effect between healthiness and preparation (p = .142) on consumption was found, however. This pattern of results was not substantially changed when hunger, dietary restraint, and BMI were entered as covariates. Discussion The results of this experimental study demonstrate that self-preparation of healthy foods increases food liking, while self-preparation of unhealthy foods does not affect food liking. It adds to previous research showing that the mere act of preparing foods leads to higher likings because people overvalue objects that they have put effort in (Dohle et al., 2014; Mochon et al., 2012; Norton et al., 2012). In addition to justification of effort, the present study suggests that self-preparation increases the health salience of foods, because when people prepare foods, they become more aware of the ingredients that constitute a food. This additional process may help people to assess whether a food is healthy or not, which also affects the liking of a food, especially for people with higher levels of dietary concerns. Thus, this study also suggests that information about foods (e.g. reading a recipe and learning that it contains healthy ingredients) is a necessary but not sufficient condition to impact the liking of healthy foods; instead, this information only takes full effect in combination with food preparation. Moreover, our study demonstrates that the effort needed to increase the liking of healthy foods can be minimal; in fact, participants in our study only measured and mixed three ingredients.

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Our research is also in line with public health programs trying to encourage people to eat less prepared (fast) foods and more self-prepared foods instead (Kumanyika et al., 2002; Lichtenstein & Ludwig, 2010; Nestle, 2010; Smith et al., 2013). In particular, promotion of home cooking has been viewed as a major strategy to encourage healthier eating patterns. Given the modest preparation demand with the food used in this study, it is likely that minimal food preparation involving healthy foods at home would be adequate to increase the liking of these foods. Thus, public health programs could promote home food preparation by, for example, providing families with simple but healthy recipes in order to foster heathy eating at home (for an excellent example, see Burrows, Bray, Morgan, & Collins, 2013). In addition, workplaces and schools could also be involved in nudging healthy food preparation (a) by offering places for “built-your-own” sandwiches, salads or wraps from healthy items in cafeterias, (b) by renovating cafeterias to allow for preparation of cooked meals from raw ingredients, rather than just reheating of prepared foods (Lichtenstein & Ludwig, 2010), (c) by involving students in school lunch preparation, (d) by incorporating home economics, gardening or cooking classes as part of the school curriculum (Hartmann et al., 2013; Jaenke et al., 2012; Lichtenstein & Ludwig, 2010; Smith et al., 2013), or (e) by providing (young) people recipes how to combine healthy convenience items with foods prepared from scratch to minimize both time and cost (Smith et al., 2013). Because this study involved a sample of young women only, it is unclear if the results would also generalize to other samples. Due to intercultural differences, an increase in perceived healthiness due to self-preparation could also lead to a decrease in liking in cultures or samples with a strong unhealthy=tasty intuition (Werle, Trendel, & Ardito, 2013). In addition, it would be important to examine if similar results can be found for children, because children’s liking for 16

fruit and vegetable is often low (Bucher et al., 2014; Cooke & Wardle, 2005). Recent findings from an experimental study, in which children between the ages 6 to 10 were involved in food preparation (van der Horst, Ferrage, & Rytz, 2014), are promising, however. In this study, a lunch meal (pasta, breaded chicken, cauliflower, and salad) was either prepared by the parent alone, or the child prepared the meal with the assistance of the parent. Children who were involved in the lunch preparation consumed significantly more salad and chicken (but also more calories). The results also showed that cooking duration was positively associated with eating duration and overall meal liking. Because children care less about the healthiness of foods (Cooke & Wardle, 2005), it is unlikely that higher consumption in this study was due to a higher health salience of the prepared food; instead, is more likely that effort, self-efficacy, positive emotions, or the spending time with the parent played a major role for the increase in consumption. Future research is needed to examine the mechanism and boundary conditions of foodpreparation on liking and consumption in more detail. As previously suggested (Norton et al., 2012), it is likely that the mechanism of the process driving the IKEA effect might vary between different products. Compared to assembling furniture or other products, preparing food is an activity that many people do on a regular basis. In addition, self-prepared food is often shared with other people, and sometimes used to impress peers and family. Thus, it is likely that feelings of competence are also associated with self-prepared food products. This notion is supported by a study by Mochon et al. (2012) who demonstrated feelings of competence play a mediating role between labor and liking for self-made products. Thus, involvement in food preparation may only increases liking in a supportive, non-threatening environment that fosters feelings of competence. These feelings might be threatened when a recipe is too difficult, or 17

when other people make evaluative judgments on people’s cooking attempts. It is also possible that there might be a tipping point at which too much preparation leads to less liking because a person feels too stressed to enjoy the preparation of a meal. This tipping point might vary and may depend, for example, on people’s cooking skills. Moreover, the healthy food that was used in this study was rather sweet. Because the mechanism that led to a higher liking of the self-prepared healthy food —higher health salience—should also be triggered when people are asked to prepare healthy but savory foods such as vegetables, it is likely that the findings of the present study also transfer to other types of foods. However, the variability of the food, along with the variability of the time and skills involved in the preparation are potential topics for future research. In addition, future studies could explore whether involvement in meal preparation can be seen as a strategy to overcome stronger food aversions in children, such as picky eating and as food neophobia (van der Horst, 2012; van der Horst et al., 2014). In contrast to Dohle et al. (2014), we found no significant effect of food preparation on consumption; for the healthy milkshake, we expected that the higher liking would also influence consumption. While the pattern of results matched our expectation, this result was not significant. This finding might be due to the fact that participants’ consumption was not only influenced by liking but also by other factors; in fact, some of the participants told us after the experiment was over that their consumption was also driven by the concern that left-overs might be thrown away. Because we also found no increases in the consumption of the self-prepared unhealthy shake, however, this study corroborates the idea that food preparation might be a tool to foster healthy eating.

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This study was designed to mirror mundane situations in which people often consume prepared, ready-to-eat foods instead of self-prepared foods. For special occasions, however, it is likely that food will be enjoyed more if someone else prepares it, especially if the other person is a significant other, or if the food is part of a ritual (Vohs, Wang, Gino, & Norton, 2013). The result of this study might also depend on people’s nutrition knowledge, i.e. the knowledge about which ingredients are healthy and unhealthy. Although knowledge was not measured in this study, it is plausible that in this sample of female participants recruited at a university, nutrition knowledge was fairly high. For individuals with low nutrition knowledge, it is possible that food preparation will lead to higher liking even if the food is unhealthy. Additional research utilizing more diverse samples is needed to explore the range, meaningfulness, and applicability of foodpreparation as an intervention strategy to increase liking for healthy foods. Moreover, in order to maximize experimental variance, the ingredients used for the two milkshakes differed markedly in terms of healthiness. If the line between healthy and unhealthy is more blurred, however, because a food contains both healthy and unhealthy ingredients, health salience might become secondary to the effort it takes to prepare the food. Many people— especially those high in dietary restraint—erroneously believe that eating healthy foods such as fruits and vegetables in addition to unhealthy ones can decrease a meal's calorie count, reflecting a health halo of healthy foods (Chandon & Wansink, 2007; Chernev, 2011; Rozin et al., 1996). In fact, the healthy ingredients of the high-calorie milkshake in Dohle and colleagues study (2014) may have produced a halo effect, so that self-preparation resulted in higher linking although the shake was not particularly healthy. This halo-effect might be particular disadvantageous for restrained eaters, because it might undermine their weight loss attempts.

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Thus, a noteworthy caveat of the present research is that participants’ perception of the healthiness of a food may not necessarily match the actual healthiness of the food. Although this study only looked at food preparation, this paper also extents the literature on the IKEA effect (Franke, Schreier, & Kaiser, 2010; Norton et al., 2012). The results of this study suggest that is possible that the IKEA effect is even further enhanced if the parts of a product are very special or valuable, leading, in more general terms, to higher ‘part salience’. Building furniture from high-quality parts, knitting a scarf using expensive cashmere yarns, or customizing a road bike with expensive gearshifts and rims might increase liking of these objects because of the higher salience of the valuable parts during production. Conclusion Ingredients of foods are not particularly salient in many everyday situation in which people consume prepared or ready-to-eat meals. This study shows that minimal food preparation increases the salience of ingredients; as a result, people become more aware about their healthiness. These results bolster recent calls for specific programs that encourage people to cook and eat more food at home. Programmatic efforts promoting self-preparation of healthy meals, however, should take into account that financial resources and time available for cooking are often limited. More research is needed to examine in more depth, and for longer periods, the effects of regular food preparation in schools, workplaces or home settings, as well as their potential for increasing the liking of disliked, but healthy foods.

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Table Table 1. Least Squares Regression Results for Mediated Moderation Analysis DV:

DV:

DV:

Liking

Perceived Healthiness

Liking

b

t

b

t

b

t

Preparation (IV1)

0.37

0.22

1.22

0.68

-0.19

-0.11

Healthiness (IV2)

0.87

0.52

19.13

10.65***

-2.88

-1.24

IV1 x IV2

4.38

2.63**

6.05

3.37**

3.13

1.81†

Perceived Healthiness (MEV)

0.20

2.29*

IV2 x MEV

0.05

0.61

Notes: IV = independent variable, DV = dependent variable, MEV = mediator variable. † p < .10, * p < .05, ** p < .01, *** p < .001.

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Figure 1 (a)

(c)

(b)

(d)

Figure 1. Effect of experimental conditions on (a) liking, (b) perceived healthiness, (c) estimated calorie content, and (d) consumption. Error bars indicate the standard error of the mean. †

p < .10, * p < .05, ** p < .01, *** p < .001.

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Figure 2

Figure 2. Effect of experimental conditions on liking for low dietary restraint (-1 SD; left graph) and for high dietary restraint (+1 SD; right graph). † p < .10, * p < .05, ** p < .01, *** p < .001.

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