Papers by David Marchiori
Social Psychological …, Jan 1, 2010
Judgment and Decision …, Jan 1, 2009
People consistently over-eat when served a large compared with a small (appropriate) portion of f... more People consistently over-eat when served a large compared with a small (appropriate) portion of food. However, the mechanism underlying this so-called portion size effect is not well understood. We argue that the process of anchoring and adjustment naturally describes this effect, such that the size of a presented portion works as an anchor that strongly influences consumption. The classical anchoring and adjustment paradigm was applied to six hypothetical eating situations. Participants were asked to imagine being served either a small or a large portion of food (i.e., low and high anchor) and to indicate whether they would consume more or less than this amount. Then, they indicated how much they would eat. These estimates were compared with a no-anchor condition where participants did not imagine a specific portion size but only indicated how much they would eat. In addition, half of participants in the anchoring conditions received a discounting instruction stating that the portion size they had been asked to imagine was randomly selected and thus not informative for their consumption estimate. As expected, participants who imagined to be served larger portions estimated to consume significantly more food than participants in the no-anchor condition, and participants who imagined to be served smaller portions estimated to consume significantly less food than participants in the no-anchor condition. The discounting manipulation did not reduce this effect of the anchors. We suggest that the process of anchoring and adjustment may provide a useful framework to understand the portion size effect and we discuss implications of this perspective.
Journal of public health (Oxford, England), Jan 17, 2015
Recognizing the mindless nature of many food decisions, it has been suggested that attempts to in... more Recognizing the mindless nature of many food decisions, it has been suggested that attempts to increase healthy eating should not focus on convincing people what is 'right' but rather aim to adjust the environment such that people are automatically directed toward healthy choices. This study investigated a nudge aiming to promote healthy food choices in train station snack shops. The nudge involved a repositioning of food products: healthy foods were placed at the cash register desk, while keeping unhealthy products available elsewhere in the shop. Three snack shops were included: a control condition; a nudge condition repositioning healthy products and a nudge + disclosure condition employing the same nudge together with an explanatory sign. Next to examining its effectiveness during 1 week, the study assessed customers' acceptance of the nudge. Controlling for a baseline week, more healthy (but not fewer unhealthy) products were sold in both nudge conditions, with no d...
Appetite, 2015
People eat more from large than from small packs, which is known as the pack size effect. We hypo... more People eat more from large than from small packs, which is known as the pack size effect. We hypothesized that providing a serving size recommendation would reduce the influence of the pack size on consumption and would thus diminish the pack size effect. Moreover, we hypothesized that a pictorial serving size recommendation, displaying food amounts visually, would be more effective than a non-pictorial recommendation that communicates the recommended amount in grams only. We tested these hypotheses in two online experiments (N = 317 and N = 324) and in one lab experiment (N = 89). In the online experiments, participants were shown a small or a large pack of unhealthy snacks, with or without a serving size recommendation. The main outcome measure was expected consumption. Replicating the pack size effect in an online setting, we found that participants expected to consume more food from large than from small packs. Furthermore, the pack size effect was considerably stronger for men ...
Appetite, 2014
People consistently over-eat when served a large compared with a small (appropriate) portion of f... more People consistently over-eat when served a large compared with a small (appropriate) portion of food. However, the mechanism underlying this so-called portion size effect is not well understood. We argue that the process of anchoring and adjustment naturally describes this effect, such that the size of a presented portion works as an anchor that strongly influences consumption. The classical anchoring and adjustment paradigm was applied to six hypothetical eating situations. Participants were asked to imagine being served either a small or a large portion of food (i.e., low and high anchor) and to indicate whether they would consume more or less than this amount. Then, they indicated how much they would eat. These estimates were compared with a no-anchor condition where participants did not imagine a specific portion size but only indicated how much they would eat. In addition, half of participants in the anchoring conditions received a discounting instruction stating that the portion size they had been asked to imagine was randomly selected and thus not informative for their consumption estimate. As expected, participants who imagined to be served larger portions estimated to consume significantly more food than participants in the no-anchor condition, and participants who imagined to be served smaller portions estimated to consume significantly less food than participants in the no-anchor condition. The discounting manipulation did not reduce this effect of the anchors. We suggest that the process of anchoring and adjustment may provide a useful framework to understand the portion size effect and we discuss implications of this perspective.
Journal of the American Dietetic Association, 2011
Studies considering the impact of food-size variations on consumption have predominantly focused ... more Studies considering the impact of food-size variations on consumption have predominantly focused on portion size, whereas very little research has investigated variations in food-item size, especially at snacking occasions, and results have been contradictory. This study evaluated the effect of altering the size of food items (ie, small vs large candies) of equal-size food portions on short-term energy intake while snacking. The study used a between-subjects design (nϭ33) in a randomized experiment conducted in spring 2008. In a psychology laboratory (separate cubicles), participants (undergraduate psychology students, 29 of 33 female, mean age 20.3Ϯ2 years, mean body mass index 21.7Ϯ3.7) were offered unlimited consumption of candies while participating in an unrelated computerized experiment. For half of the subjects, items were cut in two to make the small food-item size. Food intake (weight in grams, kilocalories, and number of food items) was examined using analysis of variance. Results showed that decreasing the item size of candies led participants to decrease by half their gram weight intake, resulting in an energy intake decrease of 60 kcal compared to the other group. Appetite ratings and subject and food characteristics had no moderating effect. A cognitive bias could explain why people tend to consider that one unit of food (eg, 10 candies) is the appropriate amount to consume, regardless of the size of the food items in the unit. This study suggests a simple dietary strategy, decreasing food-item size without having to alter the portion size offered, may reduce energy intake at snacking occasions.
Journal of Nutrition Education and Behavior, 2012
Objective: Examine the influence of altering the size of snack food (ie, small vs large cookies) ... more Objective: Examine the influence of altering the size of snack food (ie, small vs large cookies) on shortterm energy intake. Methods: First-and sixth-graders (n ¼ 77) participated in a between-subjects experimental design. All participants were offered the same gram weight of cookies during an afternoon tea at their school. For half of the participants, food was cut in 2 to make the small item size. Food intake (number of cookies, gram weight, and energy intake) was examined using ANOVA. Results: Decreasing the item size of food led to a decrease of 25% in gram weight intake, corresponding to 68 kcal. Appetitive ratings and subject and food characteristics had no moderating effect. Conclusions and Implications: Reducing the item size of food could prove a useful dietary prevention strategy based on decreased consumption, aimed at countering obesity-promoting eating behaviors favored by the easy availability of large food portions.
Appetite, 2012
While larger containers have been found to increase food intake, it is unclear whether this effec... more While larger containers have been found to increase food intake, it is unclear whether this effect is driven by container size, portion size, or their combination, as these variables are usually confounded. The study was advertised as examining the effects of snack food consumption on information processing and participants were served M&M's for free consumption in individual cubicles while watching a TV show. Participants were served (1) a medium portion of M&M's in a small (n = 30) or (2) in a large container (n = 29), or (3) a large portion in a large container (n = 29). The larger container increased intake by 129% (199 kcal) despite holding portion size constant, while controlling for different confounding variables. This research suggests that larger containers stimulate food intake over and above their impact on portion size.
Social Psychological …, 2010
According to unconscious thought theory, complex decisions are best made after a period of distra... more According to unconscious thought theory, complex decisions are best made after a period of distraction assumed to elicit ''unconscious thought.'' Here, the authors suggest instead that the superiority of decisions made after distraction results from the fact that conscious deliberation can deteriorate impressions formed on-line during information acquisition. The authors found that participants instructed to form an impression made better decisions after distraction than after deliberation, thereby replicating earlier findings. However, decisions made immediately were just as good as decisions made after distraction, which suggests (a) that people had already made their decision during information acquisition, (b) that deliberation without attention does not occur during distraction, and (c) that ruminating about one's first impression can deteriorate decision quality. Strikingly, in another condition that should have favored unconscious thought even more, deliberated decisions were better than immediate or distracted decisions. These findings were replicated in a field study.
Judgment and Decision …, 2009
According to Unconscious Thought Theory (UTT: Dijksterhuis & Nordgren, 2006), complex decisions a... more According to Unconscious Thought Theory (UTT: Dijksterhuis & Nordgren, 2006), complex decisions are best made after a period of distraction assumed to elicit unconscious thought. Over three studies, respectively offering a con-ceptual, an identical and a methodologically ...
Appetite, 2014
Objective: The present research examined the effects of a mindfulness-based intervention to foste... more Objective: The present research examined the effects of a mindfulness-based intervention to foster healthy eating. Specifically, we tested whether a brief mindfulness manipulation can prevent the portion size effect, and reduce overeating on unhealthy snacks when hungry. Methods: 110 undergraduate participants (M Age = 20.9 ± 2.3; M BMI = 22.3 ± 2.5) were served a small or a large portion of chocolate chip cookies after listening to an audio book or performing a mindfulness exercise (i.e., body scan). Current level of hunger was assessed unobtrusively on a visual analog scale before the eating situation. Main outcome measure: Calorie intake from chocolate chip cookies. Results: When presented with a large compared to a small portion, participants consumed more cookies (+83 kcal). This was not affected by the mindfulness intervention or by hunger. However, while control participants ate more unhealthy food when hungry than when not hungry (+67 kcal), participants in the mindfulness condition did not (+1 kcal). Conclusions: Findings confirm the prevalence and robustness of the portion size effect and suggest that it may be independent from awareness of internal cues. Prevention strategies may benefit more from targeting awareness of the external environment. However, mindfulness-based interventions may be effective to reduce effects of hunger on unhealthy food consumption.
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Papers by David Marchiori