In the current eating environment, individuals are often faced with large portions of calorie-dense foods. It is well-established that oversized portions, served both within and outside of the home, lead to overeating and likely contribute to weight gain. Thus, there is a need to develop and test novel strategies to moderate calorie intake from large portion sizes, which is what we aimed to do in this study.
Considering why individuals consume more when served a large amount of food can be useful in developing strategies to moderate calorie intake from large portions. Since American men and women have the tendency to eat all of the food served (“plate-clean”), we speculated that individuals may overconsume from large portions in an effort to minimize food waste, thereby maximizing value from a meal. It is therefore likely that providing opportunities to reduce food waste, such as offering the option to take away uneaten food after a meal, could attenuate the effect of portion size on intake.
In order to test this hypothesis, we recruited 53 women to come to the lab on 4 separate occasions to consume a dinner of 5 different foods. On each occasion, we simultaneously varied the portion size of all foods served at the meal, and the different meal sizes were served in a random order across weeks. Furthermore, the participants were randomly assigned to 1 of 2 subject groups: a “doggy bag” group that had their uneaten food packaged to take away with them after the meal and were informed of this opportunity prior to each meal, and a control group that did not have the option of taking away leftovers.
We opted to package food after participants (in the “doggy bag” group) indicated that they were done eating, rather than provide the packaging with the meal so that it would more closely resemble the practice in restaurants. When meals were served, participants were told they could eat as much or as little as they liked. The amount of food consumed at each meal was carefully measured by comparing the weight of food remaining after the meal to the pre-weight, and energy intakes were determined by multiplying these value by the calorie-densities of the foods. Participants also completed a series of measures at each meal; for example, we asked participants to rate and rank the different foods served based on a variety of characteristics, such as value, palatability, and market cost.
Results showed that providing the opportunity to take away uneaten food after a meal attenuated the effects of portion size on food and energy intake. Compared to the control group, women in the “doggy bag” group ate substantially less in response to being served more food at the meals. For example, women in the control group consumed an additional 64 g and 90 kcal for every 100 g of food added to baseline amounts (until the point of maximal intake) while women in the “doggy bag” group consumed fewer than 20 g and kcal more with every additional 100 g served. When comparing intakes of the individual foods between the two groups, we observed that the influence of packaging leftovers on the portion size effect was particularly marked for chicken. It is notable that this was the food that the majority of participants rated as being of the highest value. Taken together, these results could indicate a role of value in the response to large portions, such that individuals want to preserve value by not wasting food. This speculation is corroborated by another finding from our study: the magnitude of the portion size effects for individual foods tended to be related to the perceived value of the foods.
This study demonstrated that provision of the opportunity to take away uneaten food, such as through a “doggy bag,” can be an effective method to moderate intake from large portions. The effectiveness of this strategy could be related to its ability to improve value from a meal: either by reducing waste, providing another meal, or both. This method to counter the effects of large portions may also be augmented by the subtle behavioral nudge of reminding the consumer prior to eating of the option to take away uneaten food.
These findings are described in the article entitled Doggy bags and downsizing: Packaging uneaten food to go after a meal attenuates the portion size effect in women, recently published in the journal Appetite.