Expectancy versus experience - Comparing Portion-Size-Effect during pre-meal planning and actual intake.

Research on eating behaviour has confirmed that portion size can substantially influence intake, a phenomenon known as the Portion-Size-Effect (PSE). Despite extensive research interest, there is limited understanding about the PSE on intended consumption (often measured by Expected Intake). It also remains unclear whether the presentation of food cues (e.g., Word Descriptors; Food Images) can modulate PSE during pre-meal planning. The current study addressed these questions by comparing PSE on intended versus actual consumption, with 62 participants based on a within-subject design. Participants firstly rated Expected Intake for a pasta dish of three sizes (400, 600, and 800 g), with each size presented in three different formats of food cues. The participants' actual pasta intake with the three portion sizes was tested in three ad libitum sessions over 7 weeks. The results suggested that Expected Intake increases as portion size becomes larger, following a nearly linear relationship. In comparison, the Actual Intake had a smaller increment after the presented portion size exceeded the 'appropriate' range. Relating to these results, the pre-meal PSE was found to be comparable to the actual PSE with moderate portion sizes (i.e., 600 g-400 g), but significantly stronger than the actual effect with large portion sizes. Overall, our data support the hypothesis that portion size can have a stronger influence on meal planning than actual food intake, and show that the format of food cues has considerable influence on Expected Intake. Studies of pre-meal planning should carefully consider the role of portion sizes and food cues on Expected Intake.

Portion size influences intake in Samburu Kenyan people not exposed to the Western obesogenic environment.

For people in the modernized food environment, external factors like food variety, palatability, and ubiquitous learned cues for food availability can overcome internal, homeostatic signals to promote excess intake. Portion size is one such external cue; people typically consume more when served more, often without awareness. Though susceptibility to external cues may be attributed to the modernized, cue-saturated environment, there is little research on people living outside that context, or with distinctly different food norms. We studied a sample of Samburu people in rural Kenya who maintain a traditional, semi-nomadic pastoralist lifestyle, eat a very limited diet, and face chronic food insecurity. Participants (12 male, 12 female, aged 20-74, mean BMI = 18.4) attended the study on two days and were provided in counterbalanced order an individual serving bowl containing 1.4 or 2.3 kg of a familiar bean and maize stew. Amount consumed was recorded along with post-meal questions in their dialect about their awareness of intake amount. Data were omitted from two participants who consumed the entire portion in a session. Even though the 'smaller' serving was a very large meal, participants consumed 40% more when given the larger serving, despite being unable to reliably identify which day they consumed more food. This result in the Samburu demonstrates the portion size effect is not a by-product of the modern food environment and may represent a more fundamental feature of human dietary psychology.

Results of a randomized controlled trial evaluating the effect of increasing package size on usage volume of peanut butter in older adults.

BACKGROUND: Portion and package sizes of foods generally influence energy intake in children and adults. However, little is known about this effect in older adults. This study aimed to determine the effect of increasing package size on usage volume of peanut butter in older adults. Furthermore, it is investigated whether older women and men, different age groups (<65, 65-80, and 80+), and non-overweight (BMI<25), overweight (BMI≥25) and obese (BMI>30) older adults had different responses to variation in package size. METHODS: A randomized controlled trial among 205 older adults was conducted wherein participants were randomized to either the small (350 g) (n = 103) or the large (1000 g) (n = 102) package size condition. Linear regression analyses were used to determine the association between package size condition and usage volume of peanut butter on a slice of bread. Interactions of sex, age groups and BMI categories with package size were tested to investigate differences in responses to variation in package size. RESULTS: Older adults spread on average 12.4 g (SD = 4.3) of peanut butter on a slice of bread when exposed to a small jar of peanut butter and 12.6 g (SD = 4.4) when exposed to a large jar of peanut butter (B = 0.15; 95%CI = -1.04 to 1.35). Interactions between sex, age groups or BMI categories with package size condition were not statistically significant. CONCLUSIONS: Increased package size has no effect on usage volume of peanut butter among older adults. Older women and men, different age groups within older adults, and normal-weight, overweight and obese older adults do not respond differently to variation in package size of spreads.

The portion size effect: Women demonstrate an awareness of eating more than intended when served larger than normal portions.

Large portion sizes lead to increased intake. Some studies suggest that individuals are unaware that they consume more when served larger portions. In a between-subjects design we asked female participants (N = 48) how much pasta and tomato sauce they intended to consume for lunch prior to eating. We then provided a smaller or a larger portion of the same food and invited participants to self-serve a portion into a second bowl (same size in both conditions). After eating until comfortably full, participants were shown an image of the amount they had selected at the beginning of the meal. They were then asked whether they perceived having eaten more or less than this amount, and by how much more or less they had eaten. In total 46 responses were analysed. Of the participants who received the large portion and who ate more than intended, 77% (p = .029) correctly identified eating more. However, when participants were asked to indicate by how much they had eaten above or below their intended amount, those who ate more after receiving a larger portion underestimated their intake by 25% (p = .003). These findings suggest that greater intake from a larger portion is associated with an awareness of having eaten a large quantity combined with a failure to register the actual amount consumed (in the direction of underestimation). The latter might be attributed to an error associated with the visual estimation of volume.

Perceived impact of smaller compared with larger-sized bottles of sugar-sweetened beverages on consumption: A qualitative analysis.

Sugar-sweetened beverage (SSB) consumption increases obesity risk and is linked to adverse health consequences. Large packages increase food consumption, but most evidence comes from studies comparing larger with standard packages, resulting in uncertainty regarding the impact of smaller packages. There is also little research on beverages. This qualitative study explores the experiences of consuming cola from smaller compared with larger bottles, to inform intervention strategies. Sixteen households in Cambridge, England, participating in a feasibility study assessing the impact of bottle size on in-home SSB consumption, received a set amount of cola each week for four weeks in one of four bottle sizes: 1500 ml, 1000 ml, 500 ml, or 250 ml, in random order. At the study end, household representatives were interviewed about their experiences of using each bottle, including perceptions of i) consumption level; ii) consumption-related behaviours; and iii) factors affecting consumption. Interviews were semi-structured and data analysed using the Framework approach. The present analysis focuses specifically on experiences relating to use of the smaller bottles. The smallest bottles were described as increasing drinking occasion frequency and encouraging consumption of numerous bottles in succession. Factors described as facilitating their consumption were: i) convenience and portability; ii) greater numbers of bottles available, which hindered consumption monitoring and control; iii) perceived insufficient quantity per bottle; and iv) positive attitudes. In a minority of cases the smallest bottles were perceived to have reduced consumption, but this was related to practical issues with the bottles that resulted in dislike. The perception of greater consumption and qualitative reports of drinking habits associated with the smallest bottles raise the possibility that the 'portion size effect' has a lower threshold, beyond which smaller portions and packages may increase consumption. This reinforces the need for empirical evidence to assess the in-home impact of smaller bottles on SSB consumption.

Eating less from bigger packs: Preventing the pack size effect with diet primes.

An increase in the package size of food has been shown to lead to an increase in energy intake from this food, the so-called pack size effect. Previous research has shown that providing diet-concerned individuals with a reminder, or prime, of their dieting goal can help them control their consumption. Here, we investigated if providing such a prime is also effective for reducing the magnitude of the pack size effect. We conducted two experiments in which the cover of a dieting magazine (Experiment 1) and diet-related commercials (Experiment 2) served as diet goal primes. Both experiments had a 2 (pack size: small vs. large) × 2 (prime: diet vs. control) × 2 (dietary restraint: high vs. low) between participants design. We measured expected consumption of four snack foods in Experiment 1 (N = 477), and actual consumption of M&M's in Experiment 2 (N = 224). Results showed that the diet prime reduced the pack size effect for both restrained and unrestrained eaters in Experiment 1 and for restrained eaters only in Experiment 2. Although effect sizes were small, these findings suggest that a diet prime motivates restrained eaters to limit their consumption, and as a result the pack size has less influence on the amount consumed. We discuss limitations of this research as well as potential avenues for further research and theoretical and practical implications.

Portion size and intended consumption. Evidence for a pre-consumption portion size effect in males?

Larger portions increase energy intake (the 'portion size effect'); however, the mechanisms behind this effect are unclear. Although pre-meal intentions are thought to be an important determinant of energy intake, little research has examined how much of a meal individuals intend to eat when served standard versus larger portion sizes. Three studies examined the effect of manipulating portion size on intended food consumption. In Studies 1 (spaghetti bolognese) and 2 (curry and rice) male participants were shown an image of either a standard or a larger meal and indicated how much of the meal they intended to consume. In Study 3 male and female participants were served either a standard or a larger portion of ice cream for dessert, they indicated how much they intended to consume and then ate as much of the ice cream as they desired. Regardless of being shown standard or large portion sizes, in Studies 1 and 2 participants reported that they intended to eat the majority of the meal, equating to a large difference in intended energy consumption between portion size conditions (a 'pre-consumption portion size effect'). This finding was replicated in male participants in Study 3, although females intended to eat a smaller proportion of the larger portion of ice cream, compared to the standard portion. Both male and female participants tended to eat in accordance with their pre-meal intentions and a portion size effect on actual consumption was subsequently observed in males, but not in females. The portion size effect may be observed when measuring pre-meal intended consumption in males.

Preventing the pack size effect: exploring the effectiveness of pictorial and non-pictorial serving size recommendations.

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 than for women. Importantly, when including portion size preferences as a covariate, the pictorial serving size recommendation significantly reduced expected consumption, especially when placed on a large pack, as hypothesized. The non-pictorial serving size recommendation had no effect. In the lab experiment, students received a large bag of M&M's which did or did not contain the pictorial serving size recommendation. We again included general portion size preferences as a covariate. The serving size recommendation significantly lowered the amount of M&M's that participants served themselves, but only when participants reported to have noticed the serving size recommendation. We conclude that providing a pictorial serving size recommendation can be an effective intervention strategy to reduce the pack size effect, if it attracts sufficient attention.

The portion size effect on food intake. An anchoring and adjustment process?

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.

A brief mindfulness intervention reduces unhealthy eating when hungry, but not the portion size effect.

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 (MAge=20.9±2.3; MBMI=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 (+83kcal). 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 (+67kcal), participants in the mindfulness condition did not (+1kcal). 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.

Effect of food portion on masticatory parameters in 8- to 10-year-old children.

The objective of this study was to explore differences in bite size and the amount of intraoral processing of four different foods between a reference and a double portion in 8- to 10-year-old children and, also to explore if there were differences depending on the child's weight status. The study was undertaken in 8- to 10-year-old children (n = 89). Body mass index was determined, and weight status was established based on Centers for Disease Control and Prevention(CDC) guidelines. A reference (half a banana, half a large peeled carrot, a slice of loaf cake, and half a salami stick), and a double portion of each food were offered to children in a randomized order in two different sessions. Three consecutive bites were taken and averaged. Variables in this study were bite size (g), number of cycles until swallowing, sequence duration as well as cycles/g. Comparisons were performed with Mann-Whitney, Kruskal-Wallis, and Wilcoxon tests, regressions and correlations were run. Bite size was ≈13% larger with the double portion (p ≤ .05 for salami, banana, and loaf cake). Cycles/g decreased for all foods with the double portion, although only significantly for banana and loaf cake. Normal and obese children had larger bite sizes (p ≤ .05) of banana than overweight children, while only obese had larger bites of loaf cake with the double portion. In conclusion, the bite size of foods in 8- to 10-year-old children increases (13%) when the portion size is doubled and the larger bite size leads to fewer cycles/g (8%). These effects differ among foods. These parameters do not depend on weight status.

Multisectoral Strategies Needed to Establish Healthy Portion Size Norms That Disincentivize Hyperpalatable, Energy-Dense Foods and Sugary Beverages in Food Environments Linked to Obesity and Diet-Related Chronic Diseases in the United States.

Over 40 y, Americans have consumed larger portions of hyperpalatable, energy-dense foods, sugary beverages, and meals prepared at home and away from home, which have contributed to obesity and diet-related chronic diseases in the United States (US). This perspective article explores synergies between the portion size and food matrix effects, and their associated biological, physiological, environmental, and cultural susceptibilities for populations. Thereafter, we describe evidence of US public- and private-sector initiatives to reduce, standardize, and incentivize portion size norms to align with recommended servings to promote a healthy weight for children, adolescents, and adults. Practitioners could use the Individual plus Policy, System, and Environment (I + PSE) Framework to implement multisectoral strategies for the US government, businesses, and civil society organizations to establish healthy portion size norms aligned with servings recommended by the Dietary Guidelines for Americans 2020-2025, and to disincentivize overconsumption of hyperpalatable products to reduce obesity and chronic disease risks.

Is There a "Gestalt Bias" in Indulgence? Subjectively Constructing Food Units Into Wholes (vs. Parts) Increases Desire to Eat and Actual Consumption.

In the present work we extend research into the unit bias effect and its extension-the portion size effect-by demonstrating the existence of a "Gestalt bias." Drawing on the tenets of Gestalt psychology, we show that a unit bias effect can be observed for food portions that are composed of identical basic units, but which are subjectively grouped into, or perceived as a Gestalt-a larger whole. In three studies, we find that such subjectively constructed food wholes constitute a new (perceptual) unit that is perceived bigger than the units it is constructed from, thereby prompting increased eating and desire to eat.

A review of evidence supporting current strategies, challenges, and opportunities to reduce portion sizes.

Although there is considerable evidence for the portion-size effect and its potential impact on health, much of this has not been successfully applied to help consumers reduce portion sizes. The objective of this review is to provide an update on the strength of evidence supporting strategies with potential to reduce portion sizes across individuals and eating contexts. Three levels of action are considered: food-level strategies (targeting commercial snack and meal portion sizes, packaging, food labels, tableware, and food sensory properties), individual-level strategies (targeting eating rate and bite size, portion norms, plate-cleaning tendencies, and cognitive processes), and population approaches (targeting the physical, social, and economic environment and health policy). Food- and individual-level strategies are associated with small to moderate effects; however, in isolation, none seem to have sufficient impact on food intake to reverse the portion-size effect and its consequences. Wider changes to the portion-size environment will be necessary to support individual- and food-level strategies leading to portion control.

No evidence that portion size influences food consumption in male Sprague Dawley rats.

In studies of eating behavior that have been conducted in humans, the tendency to consume more when given larger portions of food, known as the portion size effect (PSE), is one of the most robust and widely replicated findings. Despite this, the mechanisms that underpin it are still unknown. In particular, it is unclear whether the PSE arises from higher-order social and cognitive processes that are unique to humans or, instead, reflects more fundamental processes that drive feeding, such as conditioned food-seeking. Importantly, studies in rodents and other animals have yet to show convincing evidence of a PSE. In this series of studies, we used several methods to test for a PSE in adult male Sprague Dawley rats. Our approaches included using visually identifiable portions of a palatable food; training on a plate cleaning procedure; providing portion sizes of food pellets that were signaled by auditory and visual food-predictive cues; providing food with amorphous shape properties; and providing standard chow diet portions in home cages. In none of these manipulations did larger portions increase food intake. In summary, our data provide no evidence that a PSE is present in male Sprague Dawley rats, and if it is, it is more nuanced, dependent on experimental procedure, and/or smaller in size than it is in humans. In turn, these findings suggest that the widely-replicated PSE in humans may be more likely to reflect higher-order cognitive and social processes than fundamental conditioned behaviors.

Understanding the science of portion control and the art of downsizing.

Offering large portions of high-energy-dense (HED) foods increases overall intake in children and adults. This is known as the portion size effect (PSE). It is robust, reliable and enduring. Over time, the PSE may facilitate overeating and ultimately positive energy balance. Therefore, it is important to understand what drives the PSE and what might be done to counter the effects of an environment promoting large portions, especially in children. Explanations for the PSE are many and diverse, ranging from consumer error in estimating portion size to simple heuristics such as cleaning the plate or eating in accordance with consumption norms. However, individual characteristics and hedonic processes influence the PSE, suggesting a more complex explanation than error or heuristics. Here PSE studies are reviewed to identify interventions that can be used to downsize portions of HED foods, with a focus on children who are still learning about social norms for portion size. Although the scientific evidence for the PSE is robust, there is still a need for creative downsizing solutions to facilitate portion control as children and adolescents establish their eating habits.

Portion Size: Latest Developments and Interventions.

PURPOSE OF REVIEW: The aim of this review is to provide an overview of (1) underlying mechanisms of the effect of portion size on energy intake, (2) external factors explaining the portion size effect and (3) interventions and measurements aimed at food portion size. RECENT FINDINGS: Previous studies have shown that portion sizes have increased in recent decades. Many experimental studies have been conducted to unravel the mechanisms underlying the portion-size effect on food intake (e.g. the appropriateness mechanism, the 'unit bias' mechanism, the 'previous experience/expectation' mechanism, the 'visual cue' mechanism and the 'bite size' mechanism). In addition, external factors have been found to drive food portion selection and consumption (e.g. value for money, mindless eating, levels of awareness, estimation bias. Research on several interventions (ranging from 'providing information' to 'eliminating choice') have been conducted, but remain scarce, especially intervention studies in which portion size is a key focus in weight loss. Moreover, only three new instruments with respect to portion control behavior have been developed. There is considerable evidence for the portion-size effect on energy intake. However, the work on interventions targeting portion size and measurements for portion control behavior are limited. Moreover, from the literature it is not yet clear what type of interventions work best, for whom and in what context.

The Role of Social Norms in the Portion Size Effect: Reducing Normative Relevance Reduces the Effect of Portion Size on Consumption Decisions.

People typically eat more from large portions of food than from small portions. An explanation that has often been given for this so-called portion size effect is that the portion size acts as a social norm and as such communicates how much is appropriate to eat. In this paper, we tested this explanation by examining whether manipulating the relevance of the portion size as a social norm changes the portion size effect, as assessed by prospective consumption decisions. We conducted one pilot experiment and one full experiment in which participants respectively indicated how much they would eat or serve themselves from a given amount of different foods. In the pilot (N = 63), we manipulated normative relevance by allegedly basing the portion size on the behavior of either students of the own university (in-group) or of another university (out-group). In the main experiment (N = 321), we told participants that either a minority or majority of people similar to them approved of the portion size. Results show that in both experiments, participants expected to serve themselves and to eat more from larger than from smaller portions. As expected, however, the portion size effect was less pronounced when the reference portions were allegedly based on the behavior of an out-group (pilot) or approved only by a minority (main experiment). These findings suggest that the portion size indeed provides normative information, because participants were less influenced by it if it communicated the behaviors or values of a less relevant social group. In addition, in the main experiment, the relation between portion size and the expected amount served was partially mediated by the amount that was considered appropriate, suggesting that concerns about eating an appropriate amount indeed play a role in the portion size effect. However, since the portion size effect was weakened but not eliminated by the normative relevance manipulations and since mediation was only partial, other mechanisms may also play a role.