Authors Nilufer Z. Ayinoglu (Koç University, Istanbul) and Aradhna Krishna (University of Michigan) found that inconsistent portion sizes contribute to people's uncertainty about the appropriate amount to eat. "In this context of large portion sizes and consumer uncertainty about appropriate food intake, we show that size labels chosen by food and drink vendors (such as 'small-medium-large') can have a major impact on consumers' purchase and consumption behavior," the authors write. "As such, food providers' choice of size labels has many potential legislative and liability-related implications."

The researchers conducted five studies that included actual food consumption. They demonstrated that the use of different size labels for the same product affects the amount people consume.

When people consumed a large item that was labeled "small," they felt less guilty; the authors call this effect "guiltless gluttony." "An implication of our results is that consumers can continue to eat large sizes that are labeled as smaller and feel that they have not consumed too much. This can result in unintended and uninformed over-consumption, which is clearly ridden with significant health ramifications, and size labels could be contributing to the rampant obesity problems in the United States."

The authors found that the biasing effect of size labels was most pronounced when people's concern about accurate nutrition intake was not high and when people's ability to process was limited -- in other words, situations not unlike everyday life.

"Stricter size labeling laws and more vigilant monitoring of marketers' use of size labels may be needed, especially considering the limited cognitive resources available to consumers for routine food choice and consumption behavior during their other everyday endeavors," the authors conclude.

Note: If no author is given, the source is cited instead.

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