Do Weight Status and the Level of Dietary Restraint Moderate the Relationship between Package Unit Size and Food Intake?

Background: Package unit size may influence consumption. Single-serving (SS) packages, as compared to larger, standard (ST) packages, may increase awareness of what a standard serving is and assist in reducing consumption. Individuals who may be concerned about the amount they consume, such as overweight (OW) and dietary restrained individuals, may be more influenced by SS packages. Thus, the purpose of this study was to examine if weight and dietary restraint status moderate the influence of package size on consumption. It was hypothesized that SS packages would help to reduce intake in OW and/or restrained individuals as compared to normal weight (NW) and/or unrestrained individuals.

Methods: Using a 2x2x2 (unrestrained/restrained x NW/OW x SS package/ST package) between-subjects factorial design, the effects of weight and restraint status on the relationship between package unit size and food intake were examined in 64 participants in a natural environment. NW and OW, unrestrained and restrained participants (23.7+3.3 years; 81.3% white; 96.9% non-Hispanic) were randomly assigned to receive either 20 ounces of pretzels packaged in SS packages or ST packages to eat ad libitum for 4 days. Total grams of pretzels consumed was determined by subtracting pre- and post-consumption weight of packages provided.

Results: Using a 2x2x2 analysis of variance, for total grams of pretzels consumed, there was a significant interaction between package unit size and weight status (F(1,56)=7.1, p=0.01). Pairwise comparisons showed that OW participants in the ST size condition ate (p<0.05) more grams of pretzels (204.4+144.9 g) compared to OW participants in the SS condition (107.0+101.9 g). Pairwise comparisons also revealed that for participants in the ST size condition, OW participants ate (p<0.05) more grams of pretzels (204.4+144.9 g) than NW participants (112.7+58.9 g). No significant difference was found between OW and NW participants in the SS condition for grams of pretzels consumed (107.0+101.9 g vs. 158.1+104.4 g, respectively).

Conclusion: Results from this study suggest that for OW individuals, ST packages increased consumption as compared to SS packages, which did not occur for NW individuals. While SS packages may not influence OW individuals to eat less in comparison to NW individuals, replacing ST packages with SS packages may assist with reducing overconsumption.