Objective and purpose:
Although there is increasing interest in how environmental factors influence food intake, there are mixed results and misunderstandings of how proximity and visibility influence consumption volume and contribute to obesity. The objective of this paper is to examine two questions: first, how does the proximity and salience of a food influence consumption volume? Second, are proximate foods consumed more frequently because they are proximate, or are they consumed more frequently because people lose track of how much they eat?
Research methods and procedures:
The 4-week study involved the chocolate candy consumption of 40 adult secretaries. The study utilized a 2 × 2 within-subject design where candy proximity was crossed with visibility. Proximity was manipulated by placing the chocolates on the desk of the participant or 2 m from the desk. Visibility was manipulated by placing the chocolates in covered bowls that were either clear or opaque. Chocolates were replenished each evening, and placement conditions were rotated every Monday. Daily consumption was noted and follow-up questionnaires were distributed and analyzed.
There were main effects for both proximity and visibility. People ate an average of 2.2 more candies each day when they were visible, and 1.8 candies more when they were proximately placed on their desk vs 2 m away. It is important to note, however, that there was a significant tendency for participants to consistently underestimate their daily consumption of proximately placed candies (−0.9) and overestimate their daily consumption of less proximately placed candies (+0.5).
These results show that the proximity and visibility of a food can consistently increase an adult's consumption of it. In addition, these results suggest that people may be biased to overestimate the consumption of foods that are less proximate, and to underestimate those that are more proximate. Knowing about these deviation tendencies is important for those attempting effectively monitor their consumption of fat and sugar.
Clinicians and health professionals want to understand the determinants of consumption volume as a foundation for effective nutrition education and counseling.1 Although taste,2, 3 mood,4, 5 stress,6 social context,7 and role models8 have been shown to influence consumption volume, it is not clear how a food's proximity or visibility influences how much one consumes and how much one believes he/she has consumed. Existing findings related to proximity and visibility are largely inconsistent.
For instance, when comparing food storage habits in homes of obese and non-obese families, Terry and Beck's9 first study showed food to be more visible in the homes of obese families, but their second study showed the opposite. A more recent experiment10 indicated that accessible food is often eaten more frequently, but there was no systematic evidence whether this was related to poor consumption monitoring or simply due to the convenience of the product.
Some indirect evidence exists that highly salient, stockpiled and accessible foods are eaten more frequently than less salient foods.11 Yet this was only found to be the case with convenient-to-consume foods such as chips, granola and juice and was not with less convenient-to-consume foods such as popcorn, soup and refrigerated cookie dough. Although such results suggest that consumption convenience can lead to increases in consumption frequency, it may be that proximate foods can be consumed with an increased frequency because they are more quickly consumed and more easily forgotten. Developmental psychology has shown that the more effort or time invested in a unique activity, the more it is likely to be recalled.12 As an analogue, it may be that a person who has to walk to another table each time he/she wants a snack may be more likely to remember how many snacks they have eaten compared to a person who only has to reach for a snack that is in a bowl in front of them.
This raises two questions that are relevant for clinicians, dieters and nutritionally conscious individuals. First, do people eat more when a food is within sight, or when it is within reach? Second, are increases in proximity-driven consumption associated with systematic biases in how much people believe they have eaten?
The participants were 40 female staff members (42.2±11.3 years) from across six different departments at the University of Illinois at Urbana-Champaign. Staff members were recruited by an e-mail which asked them whether they would be involved in a study related to candy. In exchange, they were told they would be given a free candy dish filled with chocolates and a $10 gift certificate to a local restaurant (the Spice Box).
Those who claimed to typically consume three or more pieces of candy each week were personally contacted and told they would be periodically asked about their candy preferences over a 4-week period. They were also told that as a thank you, they would be given individually wrapped chocolates (candy ‘kisses’) over that time period with the only stimulation being that because of ‘cost constraints’ they could not share them with others or take them home. They were told that there were a number of people involved in the study and that their candy dishes would be rotated with others at the end of every week and that it might even change places in their office. They were asked to leave the bowl wherever it might be relocated.
The study utilized a 2 × 2 within-subject design with repeated measures where visibility (visible vs non-visible) was crossed with the proximity (proximate vs less proximate) of the food's location relative to each participant. Visibility was manipulated by placing the chocolates in covered bowls that were either clear or opaque. Proximity was manipulated by placing the chocolates on the desk of the participant or 2 m from the desk of the participant at roughly the same level as desk level. A distance of 2 m was chosen because it was just out of reach of the participants and necessitated them to stand up to get the candy.10 It should be noted that making an opaque bowl more proximate, might also make the candy more salient when in the clear bowl. In general, this form of salience is more one of salience than of visibility at small distances of 0.5 m vs 2 m.
In the first week of the study, participants were divided into four chocolate–placement conditions of 10 people each: (1) proximate and visible, (2) proximate and non-visible, (3) less proximate and visible and (4) less proximate and non-visible. In each condition, the participants were given a lidded container holding 30 chocolates (candy ‘kisses’).
During each day of the 4 weeks of this study, 30 chocolates were placed in 20 clear containers and 20 opaque containers and delivered to the 40 participants. The containers were replenished every afternoon after 1900 hours. They were kept in the same location for four consecutive business days (Monday to Thursday). Because of irregular Friday schedules (owing to flex-time), no intake data were collected on Friday. On the next test day, the Monday of the following week, the containers were rotated for each participant. The procedure was repeated at the end of the first, second and third week, and the study was completed on the Friday of the fourth week.
Researchers kept a daily record of the number of chocolates consumed from each container. Comparisons were made of the data collected from each location during the study period. The within-subject factor was the proximity and visibility of the chocolates; the 4 days in each location were treated as repeated measures within each condition.
At the end of each week, on a Friday morning, each participant was given a questionnaire which asked them how much they thought they had eaten over the entire week and which asked them their perceptions about the chocolates (‘it was difficult to resist eating them,’ ‘I thought of eating chocolates often,’ etc.) on 9-point scales (1=strongly disagree to 9=strongly agree). Over the 4 days for each of the 4 weeks, 16 consumption observations were obtained for each of the 40 participants. To insure that the data collected would be anonymous, the Human Subjects Committee suggested that measures of height and weight not be collected. As a result, it was not possible to determine the body mass index (BMI) of the participants and to use this in analyses.
The data about actual and perceived chocolate consumption were analyzed across the four conditions using two-way multiple analysis of variance with repeated measures (SPSS 10.2). As indicated in Table 1, manipulation checks for both proximity and visibility indicated they were successfully implemented as experimental conditions.
As a baseline, when the candies were less visible and less proximate, the average person ate 3.1 candies each day. When the bowl was more visible and more proximate, however, intake increased (see Figure 1). People ate an average of 2.5 more candies each day when they were less proximate but visible (5.6 vs 3.1; P<0.05), 1.5 more when the were proximate but non-visible (4.6 vs 3.8; P<0.05) and 4.6 more when less proximate and visible (7.7 vs 3.1; P<0.05). These results help corroborate the initial hypotheses of Terry and Beck9 regarding the effects of visibility, as well as the findings of Hearn et al.13 regarding convenience. At the same time, they also show the additive effects of the interaction between visibility and proximity.
It is also important to note that the proximity of a food biased participant's estimates of how much they thought they ate. Participants had tendencies to underestimate how many candies they ate when the food was proximate and to overestimate how many they ate when less proximate. Across both the visible and non-visible conditions, participants ate an average of 6.1 candies each day when they were proximate, but they believed they ate an average of 5.2. In contrast, when the candy was less proximate, participants ate an average of 4.3 candies, but believed they ate 4.8. This tendency to underestimate the consumption of proximately placed candies (−0.9) and to overestimate the consumption of less proximately placed candies (+0.5) were both significant (P<0.05).
The visibility and proximity of candies also influenced perceptions of chocolate consumption (recall Table 1). Regardless of whether participants could actually see the chocolates, chocolates that were sitting on the desk (vs 2 m from the desk) were rated as being more difficult to resist (4.5 vs 2.7; P<0.05), as more attention-attracting (4.7 vs 2.8; P<0.05). Visibility showed similar effects. Compared to candies in opaque containers, candies in clear containers were rated as being more difficult to resist (4.1 vs 3.1; P<0.05) and as more attention-attracting (4.3 vs 3.0; P<0.05).
One potential concern with within-subject designs is that of possible demand effects when a person experiences the different conditions of an experiment. To assess whether this is a serious concern, the comparison of all 4 weeks of data was compared with that for only the first week, when each participant was exposed to only one condition. The basic pattern of the intake results for this first week was consistent with the aggregate pattern for the entire 4 weeks. A two-way between-subject analysis of variance (with repeated measures) indicated a main effect for both proximity (P<0.5) and a marginal effect for visibility (P<0.10). This provides confidence that the influence over the 4 weeks was of a similar nature and not attributable to demand effects. Furthermore, if there were demand effects, they would have been more likely to make the results less significant and not as strong as the effects found here.
When the candies were 6 feet away from the desk, people ate more candies but tended to underestimate the number they had eaten. This raises the issue as to whether this decrease in consumption occurred because of the distance itself or because the underestimation that accompanied it. To examine this, a mediation analysis was conducted using estimated consumption as a mediator between proximity and consumption.14 In conducting this analysis, it was found that proximity had a direct influence on both consumption (P<0.05) and on estimation (P<0.05), but the influence of estimation on intake was not significant (P<0.20). Furthermore, when consumption estimation was included in a regression of proximity on to consumption, the impact of proximity remained significant (P<0.05). These results indicate that even though the consumption of a distant object is overestimated, this bias cannot account for the effect this distance had on reducing intake.
What then explains how distance influences consumption? Whereas distance and effort would explain why consumption is decreased,15 debriefing interviews indicated an additional explanation. Although some participants noted the lack of convenience as being a consideration when they decided whether to eat a chocolate, 26 of 40 (65%) noted that having 2 m between them and the candy gave them an extra second to pause and reconsider whether they were really hungry enough to want (or need) another candy. This notion that extra effort can help facilitate cognitive control is a finding that was unexpected and would not have been revealed if this was being investigated with commonly studied animal models, such as rats.16
Interestingly, the corresponding explanation as to why distance also tended to cause people to overestimate how much they had consumed was explored in debriefing interviews. When the candies were sitting on one's desk, these interviews indicated that a person typically retrieved one candy kiss at a time and ate one candy kiss at a time. When the candies were sitting 2 m away, participants often reported retrieving two (or more) candies at a time. They opened the candy jar less often, but they took more because of the increased effort. As a result, when they estimated how many candies they ate when the dish was 2 m away, they typically estimated the number of times they retrieved candies and multiplied this by two. If combined with instances when they only retrieved one, this would lead to an overestimation of how much they had consumed over the course of the week.
In extending other findings,8, 10 these results underscore that the proximity and visibility of a food can consistently increase an adult's consumption of it. Yet although they ate more, they also tended to underestimate the amount they had eaten when the candies were proximate and visible. This is consistent with past work that a basic availability bias causes people to over-represent or overestimate the incidence or quantity of items that are more salient (or available) in memory.17 Such a bias can lead people to overestimate the consumption of those foods that are less proximate to obtain (or to prepare), and to underestimate or forget those that were more proximate to consume.18
This has important implications for people who are trying to be accurate in monitoring and controlling their intake of food. These results underscore that people need to take a food's visibility and proximity into account when they try and estimate their prior consumption of it. In general, a food that is less proximate to consume – say cookies in the cupboard vs those on the counter – may be over-consumed relative to what one might think (or recall).
Furthermore, understanding this bias has implications for researchers studying consumption data and diary panels. These findings emphasize that it is important to account for the visibility and proximity of foods because not doing so can lead to biased consumption recall studies and biased diary panel estimates. One way to do this is to ask people to rate the visibility and proximity of the foods under investigation. These ratings can then be used as either covariates or can be used as blocking or segmentation variables.19
Whereas the tendency to underestimate one's consumption of a proximate food may be a general tendency across people, obese people may be more motivated to deny what they have eaten than non-obese people. That is, although there may be a gap in everyone's estimation of proximate foods, some populations may be more extreme in their bias than others. Although measures of BMI were not able to have been taken in this study, if such a relationship does exist, it would most likely found in future studies that use within-subject designs in field situations.
Encouragingly, if visibility and proximity increase the consumption of chocolate, it may also work for healthier foods, such as raw fruits or vegetables.20 What makes the candy dish nutritionally dangerous, might bring the fruit bowl back in vogue.
Special thanks to Paula for her help in data collection.
About this article
Assessing self-regulation strategies: development and validation of the tempest self-regulation questionnaire for eating (TESQ-E) in adolescents
International Journal of Behavioral Nutrition and Physical Activity (2014)