Portion size does not influence food consumption in rats

Abstract

In studies of eating behavior that have been conducted in humans, the tendency to consume more when given larger portions of food, known as the portion size effect (PSE), is one of the most robust and widely replicated findings. Despite this, the mechanisms that underpin it are still unknown. In particular, it is unclear whether the PSE arises from higher-order social and cognitive processes that are unique to humans or, instead, reflects more fundamental processes that drive feeding, such as conditioned food-seeking. Importantly, studies in rodents and other animals have yet to show convincing evidence of a PSE. In this series of studies, we used several methods to test for a PSE in adult male Sprague-Dawley rats. Our approaches included using visually identifiable portions of a palatable food; training on a plate cleaning procedure; providing portion sizes of food pellets that were signaled by auditory and visual food-predictive cues; providing food with amorphous shape properties; and providing standard chow diet portions in home cages. In none of these manipulations did larger portions increase food intake. In summary, our data indicate that a PSE does not appear to be present in rats or, if it is, it is more nuanced, dependent on experimental procedure and/or smaller in size than it is in humans. In turn, these findings suggest that the widely-replicated PSE in humans may be more likely to reflect higher-order cognitive and social processes than fundamental conditioned behaviors.\n\nHighlightsO_LIPortion size effect (PSE) refers to increased food intake induced by large portions.\nC_LIO_LIAlthough widely replicated in human feeding studies, it may not exist animals.\nC_LIO_LIPresence of a PSE in animals would shed light on mechanisms, which are not known.\nC_LIO_LIHere, we find no evidence of PSE in rats under a number of experimental conditions.\nC_LIO_LIThis suggests that the human PSE is more likely due to socio-cognitive processes.\nC_LI