In deciding how much to eat, people are influenced by environmental cues. The unit size of food (i.e., the number of units in which a given amount of food is divided) provides such a cue. Previous research showed that given equal caloric and volumetric content, smaller units of food tend to reduce food consumption. We propose that the unit size of food impacts intake as it influences perceptions of impulsiveness and appropriateness. Our analysis is based on three experimental studies, all employing between subject designs. When consuming similar amounts of chocolates in studies 1 (n = 118) and 2 (n = 124), both studies show that consumption of five small units of chocolates is considered to be more impulsive, excessive and less appropriate than consuming one large unit of chocolate. Results of a third study (n = 165) indicate that about 23% less chocolate is eaten when it is presented in small unit size vs. a large unit size and this effect is mediated by perceptions of impulsivity. All three studies suggest that perceptions of impulsivity and excess eating while eating several smaller units of food compared to one large unit might be a key factor explaining consumption effects in earlier studies on this bias.
Keywords: consumption behaviour; consumption monitoring; impulsivity; portion size; unit size bias.