Research ReportIncreasing the portion size of a packaged snack increases energy intake in men and women
Introduction
The rapid rise in the incidence of obesity and overweight (Flegal, Carroll, Ogden, & Johnson, 2002) has led to suggestions that the current eating environment promotes excessive energy intake (Peters et al., 2002, Rolls, 2003). Some elements of the environment that can encourage overeating are the availability of inexpensive high-energy foods, the wide variety of palatable foods, the high frequency of consuming meals outside the home, eating between meals (snacking), and the large portion sizes of many energy-dense foods. It is thought that portion size, in particular, may play a role in overeating because the growth in portion sizes of many foods in supermarkets and restaurants has coincided with the surge in obesity rates in the United States (Young and Nestle, 2002, Nielsen and Popkin, 2003, Smiciklas-Wright et al., 2003). A key question is whether increases in portion size have a direct effect on the amount of food consumed.
There are only limited data available from controlled studies of the influence of portion size on intake (Rolls, 2003). In a recent study, on different days we offered adults one of four different portions of macaroni and cheese for lunch, and found that the bigger the portion, the more that they ate. The participants consumed 30% more energy (676 kJ; 162 kcal) when offered the 1000 g portion compared to the 500 g portion (Rolls, Morris, & Roe, 2002). It could be argued that the effects of portion size on intake are specific to foods like macaroni and cheese that are amorphous in shape. It has been shown that it is particularly difficult to judge the portion size of such foods, especially when the portions are large (Slawson & Eck, 1997). The purpose of the present study was to test whether intake is also influenced by portion size when the food is presented in a clearly defined package, such as is common for snack foods.
Snack foods are of particular interest because they may be contributing to the obesity epidemic. Nationally representative surveys in the United States show that between 1978 and 1996, both energy intake from snacks and the proportion of daily energy intake consumed as snacks have increased in young adults (Zizza, Siega-Riz, & Popkin, 2001). The main factor contributing to this increase was a 26% increase in the energy consumed per snacking occasion. One explanation for the increased energy intake from snacks is that the energy density (energy per g) of the snacks has increased (Zizza et al., 2001); another possibility is that the increased package size of snacks directly influenced the amount eaten.
Although the effects of package size on snack intake have not previously been studied in a randomized controlled experiment, there have been indications that package size can affect consumption of snacks. In one study, when people were asked how many candies they would eat while watching a movie, the number they chose increased as the package size increased (Wansink, 1996). In another study conducted in a movie theater, the portion size of popcorn given to participants was directly related to the amount consumed (Wansink & Park, 2000).
In the present study, we tested the effect of the portion size of a snack food on intake by providing subjects with packages of potato chips (crisps) in five commercially available sizes. We hypothesized that snack intake would increase as the package size increased, and that there would be little decrease in energy consumption later in the day in compensation for this elevated intake.
Section snippets
Subjects
We recruited potential subjects by newspaper advertisements, and interviewed them by telephone to determine that they met the inclusion criteria: aged 20–45 y, regularly ate three meals per day, regularly snacked between meals and liked potato chips, were not dieting to gain or lose weight, were not using medication known to affect food intake or appetite, were not athletes in training, were not pregnant or lactating, had no food allergies or food restrictions that would affect food intake, and
Subject characteristics
Sixty-eight subjects were enrolled in the study. Five subjects withdrew from the study for personal reasons or because they could not attend according to schedule. Thus, 63 subjects completed the study. Three subjects were excluded from the analysis for repeatedly having low intakes at the snack (<10 g at three or more sessions). The final sample consisted of 60 subjects, whose characteristics are shown in Table 1.
Snack intake
The package size of the potato chips had a significant effect on snack intake (p
Discussion
The results of this study demonstrate that the portion size of a packaged snack directly affects the amount of that snack that is consumed. Furthermore, in most cases individuals did not significantly reduce intake at dinner to compensate for the increased energy intake from the snack. The only exception was that in male subjects, mean energy intake decreased at dinner following the largest snack package. Overall, however, increasing the portion size of the snack increased short-term energy
Acknowledgements
This work was supported by the National Institutes of Health, grant DK59583.
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