The portion size effect on food intake is robust to contextual size information

Differences in Portion Sizes in Brazil, France, and the USA

Portion size is recognized as a major determinant of food intake, at least over the short term, and could be related to overconsumption and obesity. In this study, we developed and evaluated a new visual measure of portion size (PS), examined whether the PS of chicken, ice cream, and soda varied among people in Brazil, France, and the USA, and tested whether PS was related to gender, body mass index, body weight, and socioeconomic status. We conducted a cross-sectional study using online convenience samples of university students (total N = 1391). Across all three foods, French personal and country PSs were significantly smaller than the other three countries. Estimated country PS was reliably larger than personal PS. Women's personal PSs were smaller than men's, but women's and men's estimates for country PS were similar. French personal and country PSs were the lowest. Some PSs had a weak but significant correlation with SES but were not significantly related to either weight or BMI. The study confirms French-American differences in personal PS and demonstrates that perceived norms correspond to individual PS.

People serve themselves larger portions before a social meal

One of the most powerful influences on food intake yet identified is the presence of familiar others at an eating occasion: people eat much more when they eat with friends/family than when they eat alone. But why this is the case is unclear. Across two studies (Study 1: N = 98; Study 2: N = 120), we found that the mere anticipation of social interaction is all that is needed to promote the selection of larger meals, and that this occurs even when a person is alone when they make their decision. Adult women served themselves larger portions when they knew they were going to eat socially versus when they knew they were going to eat alone. These data suggest that how other people influence our food intake reaches beyond the specific eating context to affect pre-meal portion size decisions, suggesting that a fundamental shift is required in our thinking about social influences on eating.

Does food deprivation affect perceived size?

Exposure to food-related stimuli could lead to the triggering of a set of biological, emotional and cognitive responses. Such responses can be pronounced following food deprivation. Indeed, previous research showed that even a moderate period of food deprivation is sufficient to increase perceptual precision to detect changes along food size and to change the processing style of food-related stimuli. It is unclear, however, whether food deprivation also leads to systematic biases along the perception of food size. Here, we used two classic psychophysical methods, the method of constant stimuli and the method of adjustment, adapted to the field of food perception, to study the effect of food deprivation on average perceived food size. In two experiments, food deprived and non-deprived participants were asked to compare a series of food and non-food visual stimuli along their size. The results were inconsistent and depended upon the method used. When found, small bias effects resulted in food stimuli perceived as bigger following food deprivation. The results show that unlike the reliable effects motivational factors have on perceptual precision and on perceptual processing style, they have an inconsistent influence on average perceived food size.

Portion size effects vary: The size of food units is a bigger problem than the number

While it is well-known that larger food portions lead to increased consumption (i.e., the portion size effect), previous studies confound the effect of the size and the number of food units making up the larger portion. Moreover, empirical tests of the mechanism underlying the portions size effect are scarce. In response to these shortcomings, we present three experiments that test the impact of food unit-size and unit-number on consumption of increasingly large portion sizes, and assess whether perceptions of quantity (driven by unit size or number) mediate the portion size effect. Study 1 (n = 185), tracking actual consumption, shows that the portion size effect is determined more by unit-size than unit-number. Relative consumption ratios are higher when participants were served portions made up of enlarged food units compared to more food units. Since perceived quantity and consumption are thought to be negatively related, Study 2 (n = 193) reveals that consumers' quantity perceptions of portions are lower for unit-size (vs. unit-number) increases. Study 3 (n = 189) considers both perceived quantity and consumption and demonstrates that perceived quantity indeed mediates the effect of food portion size on consumption. Finally, this study also shows that encouraging consumers to focus perceptually on size when portion size increases are in terms of unit-size, or focus on number when portion size increases are in terms of unit-number, supports them in increasing quantity perceptions and decreasing actual consumption. Hence, manipulating the perceptual focus of consumers helps to mitigate the portion size effect. The findings contribute to literature on the portion size effect and numerosity heuristic, and provide practical insights on food packaging so to tackle the obesity crisis.

Potential moderators of the portion size effect

AIM

The robust effect of portion size on intake has led to growing interest in why individuals consume more food when served larger portions. A number of explanations have been proposed, and this review aims to provide insight into potential underlying factors by summarizing recent studies testing moderators of the portion size effect.

SUMMARY OF FINDINGS

Provision of portion size information, such as through labeling or training in portion control, failed to attenuate food intake in response to increasing meal size. This indicates that a lack of knowledge about appropriate portions may not be sufficient to explain the portion size effect. In contrast, there is evidence for a role of decision making in the response to large portions, with value being one consideration of importance. The portion size effect may be more closely related to the inherent value of food than monetary value, since provision of the opportunity to take away uneaten food after a meal, which can reduce food waste, attenuated the portion size effect but variations in pricing did not. A number of studies also support an influence of orosensory processing on the portion size effect; large portions have been shown to relate to increased bite size and faster eating rate. Reduced oral processing time when consuming large portions could contribute to the effect by delaying sensory-specific satiety. Findings from a recent study supported this by demonstrating that sensory-specific satiety did not differ between larger and smaller portions despite substantial differences in intake.

CONCLUSIONS

A number of moderators of the portion size effect have been identified, including factors related to the environment, the food, and the individual. It is likely that multiple variables contribute to the response to large portions. Future research should aim to determine the relative contribution of explanatory variables across different contexts and individuals.

Doggy bags and downsizing: Packaging uneaten food to go after a meal attenuates the portion size effect in women

Serving larger portions leads to increased food and energy intake, but little is known about strategies to moderate this response. This study tested how the effect of portion size on meal intake was influenced by providing the option to take away uneaten food in a "doggy bag" (to-go container). Women were randomly assigned to one of two subject groups: a To-Go Group (n = 27) that was informed before each meal that their leftover food would be packaged to take away after the meal, and a Control Group (n = 26) that was not given this option. In a crossover design, subjects came to the lab once a week for four weeks to eat a dinner composed of five foods. Across meals, the portion size of all foods was varied (100%, 125%, 150%, and 175% of baseline). Results showed that the portion size effect, defined as the trajectory of intake across the weight of food served, differed significantly by subject group (P ≤ 0.025). In the Control Group, increasing the portion size of all foods led to substantial increases in intake (P < 0.0001); for every 100 g added to the baseline portion, women in this group consumed an additional mean (±SEM) of 64 ± 12 g of food and 90 ± 19 kcal, until intake leveled off. In contrast, intake of women in the To-Go Group increased by only 17 ± 12 g and 19 ± 18 kcal for every additional 100 g served; these increases did not differ significantly from zero (P > 0.15). Thus, the effect of portion size on intake was attenuated in the To-Go Group compared to the Control Group. These data indicate that packaging uneaten food after a meal could be an effective strategy to reduce overconsumption from large portions.

Food deprivation reduces the susceptibility to size-contrast illusions

Hunger, caused by mild amount of food deprivation, is an everyday physiological state familiar to us all. Ongoing research has pinpointed the way hunger affects people's physiological functions as well as their attitudes and allocation of attention toward domain-specific, food-related objects. Yet, little is known about the way food deprivation affects basic perceptual abilities. Here, we utilized size-contrast visual illusions commonly associated with food to explore the way deprivation affects relative processing of food size. In two experiments (N_exp1 = 32 females, mean age: 24.31; N_expt2 = 41 females, 40 males, mean age: 23.84), we examined the effect food deprivation has on participants' susceptibility to the Delboeuf illusion, which biases the perceived size of a neutral or of a food-related object when it is placed within the context of another object (e.g., a pizza is perceived as smaller when placed on a larger plate or tray). The results showed that food deprivation reduces the illusory bias for food-related but not for neutral stimuli. Such reduction in the illusory effect indicates reliance on analytic, rather than on relative processing style, for domain-specific stimuli when in the state of hunger.

The effect of the labelled serving size on consumption: A systematic review

Guidance for food consumption and portion control plays an important role in the global management of overweight and obesity. Carefully conceptualised serving size labelling can contribute to this guidance. However, little is known about the relationship between the information that is provided regarding serving sizes on food packages and levels of actual food consumption. The aim of this systematic review was to investigate how serving size information on food packages influences food consumption. We conducted a systematic review of the evidence published between 1980 and March 2018. Two reviewers screened titles and abstracts for relevance and assessed relevant articles for eligibility in full-text. Five studies were considered eligible for the systematic review. In three of the included studies, changes in serving size labelling resulted in positive health implications for consumers, whereby less discretionary foods were consumed, if serving sizes were smaller or if serving size information was provided alongside contextual information referring to the entire package. One study did not find significant differences between the conditions they tested and one study suggested a potentially negative impact, if the serving size was reduced. The influence of labelled serving size on consumption of non-discretionary foods remains unclear, which is partially due to the absence of studies specifically focusing on non-discretionary food groups. Studies that investigate the impact of serving size labels within the home environment and across a broad demographic cross-section are required.

Comparing the portion size effect in women with and without extended training in portion control: A follow-up to the Portion-Control Strategies Trial

Following a 1-year randomized controlled trial that tested how weight loss was influenced by different targeted strategies for managing food portions, we evaluated whether the effect of portion size on intake in a controlled setting was attenuated in trained participants compared to untrained controls. Subjects were 3 groups of women: 39 participants with overweight and obesity from the Portion-Control Strategies Trial, 34 controls with overweight and obesity, and 29 controls with normal weight. In a crossover design, on 4 different occasions subjects were served a meal consisting of 7 foods that differed in energy density (ED). Across the meals, all foods were varied in portion size (100%, 125%, 150%, or 175% of baseline). The results showed that serving larger portions increased the weight and energy of food consumed at the meal (P < .0001), and this effect did not differ across groups. Increasing portions by 75% increased food intake by a mean (±SEM) of 111 ± 10 g (27%) and increased energy intake by 126 ± 14 kcal (25%). Across all meals, however, trained participants had lower energy intake (506 ± 15 vs. 601 ± 12 kcal, P = .006) and lower meal ED (1.09 ± 0.02 vs. 1.27 ± 0.02 kcal/g; P = .003) than controls, whose intake did not differ by weight status. The lower energy intake of trained participants was attributable to consuming meals with a greater proportion of lower-ED foods than controls. These results further demonstrate the robust nature of the portion size effect and reinforce that reducing meal ED is an effective way to moderate energy intake in the presence of large portions.

The effect of television watching and portion size on intake during a meal

Watching television while eating and eating from larger portion sizes of food are factors that have been found to independently increase food intake. When combined, these factors may further enhance consumption. This investigation, using a 4 × 2 × 2 mixed factorial design, with a between-subjects factor of order of conditions and within-subjects factors of television watching (NO TV and TV) and portion size (SMALL and LARGE), tested the independent effects and interaction of these factors in seventeen women and three men (21.6 ± 2.3 kg/m², 22.3 ± 3.7 years, 80% white and 95% non-Hispanic). In each condition, participants had 30 min to eat a meal containing macaroni and cheese and salad with dressing. For NO TV, participants sat for 30 min while eating, while for TV, participants viewed a 30-min show containing no food cues while eating. In SMALL the meal provided 1083 kcal, while in LARGE the meal provided 200% of SMALL. Mixed factorial analysis of variance revealed a significant main effect of portion size on grams and energy consumed of the total meal. Participants consumed more grams (577.9 ± 150.5 g vs. 453.1 ± 96.6 g; p < 0.001) and energy (903.9 ± 270.4 kcal vs. 734.6 ± 187.1 kcal; p < 0.001) in LARGE as compared to SMALL. No significant effect of television watching or interaction of television watching and portion size was found. Results of this study suggest that to assist with reducing intake, smaller portion sizes should be implemented in all types of eating situations.