This study addresses two questions about sub-packaging: (i) Do 100-calorie packages reduce the calorie intake of overweight individuals differently than normal-weight individuals? (ii) Do they enable individuals to accurately track intake? Thirty-seven undergraduates were randomly given either four 100-calorie packages of crackers or one 400-calorie package of crackers to eat while watching television. The average participant ate 25.2% (75.1 calories) less when given four 100-calorie packages of crackers than when given one 400-calorie package (P = 0.006). In addition, much of this influence was driven by overweight participants whose intake decreased by 54.1%. However, all of the participants underestimated their consumption by 60% or more, indicating that sub-packaging does not appear to increase one's accuracy in estimating how much is consumed. Smaller sized sub-packaging most greatly benefits those who are overweight, yet it does so without making people more aware of how much they have eaten.
Environmental cues are important drivers of food intake (1,2). Previous research, for example, documents dramatic increases in consumption when people serve and eat from larger- vs. smaller-sized containers—such as packages, plates, and bowls (2,3,4). One reason why larger-sized containers lead to increased intake is that they provide an implicit suggestion of how much is appropriate to serve oneself and consume. In addition, larger containers can bias how people monitor or estimate the amount of food that is served and consumed (5,6). Thus, perhaps if people were given scalable, smaller packages of food—such as four 100-calorie packages instead of one large 400-calorie package—they may consume less because these packages would suggest smaller consumption norms and would allow better monitoring of how much is being consumed.
Although the food industry introduced sub-packaging—such as the 100-calorie pack—to help reverse the trend of overeating, there has been mixed evidence of its effectiveness (3,7,8,9,10). In part, previous studies might provide inconsistent results because they have not considered individual characteristics—such as BMI. That is, there is evidence suggesting that overweight people reported that they were more likely to follow external cues (e.g., stop eating when they run out of a beverage) than were normal-weight people (11,12). Thus, if obese people are more likely to rely on external cues to stop eating, they could benefit the most from sub-packaging, since it could provide a better opportunity to track how much one eats (11,12,13).
This study examines whether sub-packaging decreases a person's intake and whether this depends on a person's BMI. Specifically, we hypothesize that sub-packaging decreases participants' intake because it helps them keep better track of how much they have eaten. In addition, we hypothesize that sub-packaging has the greatest influence on those who are overweight, because they are more likely to rely on external cues to stop eating.
Subjects and Methods
In recruiting for this institutional review board-approved study, the only inclusion criterion was being a student. In exchange for partial course credit, 42 undergraduates from seven classes were recruited. The 10 experimental sessions involved four to five participants, and each session was randomly assigned to a condition. Participants were either given one large 400-calorie package of crackers or a similar-sized package that had then been sub-divided into four smaller 100-calorie sub-packaged crackers. Participants were given no nutritional (e.g., caloric) information for the crackers. Because the experimenter prepackaged each package of crackers, the total number of crackers was identical across both conditions.
Participants were told that they would watch a television comedy and would be asked questions about it. They were also told—in an offhanded manner—that there had been a reception the night before, and there were some leftover crackers they could eat if they wished. One half of the participants were given one 400 calorie bag of crackers, and the other half was given four 100 calorie bags of crackers. After watching the 22-min show, participants completed questionnaires, and the remaining crackers were counted to calculate their caloric intake.
In addition to demographic and anthropometric questions (i.e., gender, age, height, and weight), participants were asked to estimate how many crackers they believed they consumed. We converted their estimated number of crackers to caloric intake in order to facilitate the comparison with actual caloric intake. Furthermore, participants were asked to report how long since they last ate (in h) to control for hunger. In addition, two questions were asked to determine how sated they felt: “How do you feel?” (Not very full = 1; Very full = 9) and “How much food do you think you will eat for lunch?” (Less than usual = 1; More than usual = 9). Participants were then thanked and debriefed. All analyses were performed using SPSS (version 17.0). A P value <0.05 was considered to be statistically significant.
We excluded three participants who failed to report their weight and height and two outliers who consumed >2 s.d. from the mean intake scores, leaving 37 participants (22 men, 15 women; 20.3 ± 1.1 years; mean BMI 23.8 ± 3.91 kg/m2). Fifteen of these participants were classified as overweight (≥25 BMI). There was no difference between the BMI of those assigned to the large-package condition (mean BMI 23.9 ± 4.74) and those to the small condition (mean BMI 23.7 ± 3.43), P = 0.84. Of the 16 people assigned to the large-package conditions, 37.5% were overweight, and of the 21 people assigned to the small-package conditions, 42.9% were overweight (see Supplementary Table S1 online).
A 2 × 2 (small/large package × normal/overweight BMI) analysis of covariance was conducted using covariates of gender and hunger. There was a significant main effect that could be attributed to package size; those consuming from the four smaller packages ate 25.2% less (Mcalories = 222.92, s.d. = 150.40) than those consuming from a large package (Mcalories = 298.05, s.d. = 120.46), F (1, 31) = 8.88, P = 0.006. Importantly, this effect was qualified by a significant interaction, F (1, 31) = 6.66, P = 0.02 (Figure 1). As expected, the simple effects tests revealed that overweight participants ate more crackers (Mcalories = 383.54, s.d. = 158.70) when eating from one large package than from four small packages (Mcalories = 175.97, s.d. = 115.54), F (1, 31) = 12.68, P = 0.001. In contrast, there was no difference in consumption between package conditions among the normal-weight participants, P > 0.99.
However, there was no significant difference between how much each of the two groups believed they ate, P = 0.14. This suggests that the reduction in consumption was not because sub-packaging enabled participants to better monitor their intake. The groups grossly underestimated how many crackers they had eaten by a similar degree; those with large packages underestimated their consumption by 67.0% (98.44 vs. 298.05 calories) and those with sub-packaging underestimated their consumption by 61.9% (85.00 vs. 222.92 calories). This effect did not interact with BMI, P = 0.10, suggesting that participants underestimated their intake regardless of BMI. In other words, any monitoring advantage that might be generated by small sub-packages does not appear to account for the decrease in consumption that we found among overweight individuals.
Finally, although there was no difference in terms of how they felt whether they were full, F (1, 30) = 2.92, P = 0.10, participants consuming from the four smaller packages claimed that they would eat less for their next meal, F (1, 30) = 7.18, P = 0.01. These effects were robust across BMI levels (P > 0.45). Despite eating less, they still wanted to eat less for their lunch compared to those consuming from the large, single package.
These results demonstrate that sub-packaging can indeed influence how much people eat. Consistent with Raynor and Wing (2007) (8), sub-packaging had little effect on normal-weight people. Most interesting, however, is that sub-packaging dramatically reduced snack intake most among participants who were overweight.
It was hypothesized that sub-packaging would lead people to eat less because people would be able to monitor their intake. This was not the case. Those with sub-packaging were no more accurate in estimating their food intake than those with larger packages. What may instead be occurring is that sub-packaging introduces “pause points” into one's eating. There is a potentially interesting distinction here for future research. It is important to recall that these individuals were watching an engaging television show while they were eating. It may be that under conditions of distraction, individuals allocate fewer cognitive resources to monitoring how much they eat. Instead, they merely notice how many packages they eat. Nevertheless, consistent with past findings that obese people were more likely to rely on external cues to stop eating, the perception of package count might play a crucial role for overweight participants in determining their food intake.
The impact of sub-packaging may also be moderated by dietary restraint (14,15). Whereas unrestrained eaters may consume more calories from a single large-package, restrained eaters may actually consume more from smaller packages, perhaps because they perceive the smaller packages as being “diet-friendly (15).” In future research, it is important to examine dietary restraint in combination with BMI.
This study has limitations. First, rather than measuring participants' actual height and weight, we relied on self-reported height and weight, which is prone to errors. Second, in an effort to attain the realism of a field study and to shield participants from understanding the purpose of our study, we used a between-subject design instead of a within-subject design. In addition, participants were given food while other people were also present. Nevertheless, these findings are encouraging in the fight against obesity. If sub-packaging—such as the 100-calorie package—can reduce how much overweight individuals eat as originally shown in 1996 (16), it can be worthwhile for dieters to utilize and health practitioners to suggest. The resulting outcome—eating less—is most dramatic for the people who need it most.