Research report Perceived volume, expected satiation, and the energy content of self-selected meals § Jeffrey M. Brunstrom a,b, *, Jane Collingwood a , Peter J. Rogers a a University of Bristol, England, UK b Department of Experimental Psychology, University of Bristol, 12a Priory Road, Bristol BS8 1TU, UK Introduction Meals tend to be consumed in their entirety (Krassner, Brownell, & Stunkard, 1979; Lebow, Chipperfield, & Magnusson, 1985; Wansink & Cheney, 2005). Therefore, a critical determinant of energy intake is the cognitive activity associated with meal-size selection, before a meal begins (Brunstrom, 2007). Despite the significance of these decisions, relatively little is known about the basis on which they are made. This study considers determinants of the energetic content of self-selected meals. Previously, Brunstrom et al. have quantified (calorie for calorie) the satiation (fullness) and satiety (relief from hunger) that participants anticipate from a range of commonly consumed foods (Brunstrom & Shakeshaft, 2009; Brunstrom, Shakeshaft, & Scott- Samuel, 2008). Foods differ considerably in this regard (up to a 5– 6-fold difference). Defining and measuring expectations in this way leads to some striking and provocative findings. For example, these expectations are a very good predictor of the energetic content of self-selected portions (Brunstrom & Rogers, 2009; Brunstrom & Shakeshaft, 2009). By contrast, and contrary to the prevailing view, ‘expected liking’ for 16 commonly consumed foods explained less than 1% of the variance in self-selected portions (kcal) at lunchtime (Brunstrom & Rogers, 2009). Expected satiety appears to increase as a food becomes familiar (Brunstrom et al., 2008). Presumably, these shifts in expectations can be attributed to an association that develops between the taste characteristics of a food and the post-ingestive events that occur after it has been consumed. This ‘flavour-nutrient learning’ explains why expectations are highly correlated with predictions of the ‘actual’ satiety that a food confers (Brunstrom et al., 2008) and it accounts for the finding that expectations can be learned under laboratory conditions (Wilkinson & Brunstrom, 2009). In addition to effects of prior experience, judgments might also be influenced by other general or ‘unlearned’ food characteristics. In this paper we focus on the role of ‘perceived volume.’ Our interest in this topic stems from a number of studies exploring determinants of satiation and meal size. Consistently, researchers find that energy intake is reduced when low energy-dense foods are consumed (Bell, Castellanos, Pelkman, Thorwart, & Rolls, 1998; Fisher, Liu, Birch, & Rolls, 2007; Leahy, Birch, Fisher, & Rolls, 2008; Rolls, Roe, & Meengs, 2006; Stubbs, Johnstone, O’Reilly, Barton, & Reid, 1998). In a typical study the energy density of a test food is manipulated covertly. When participants are offered free access to a low energy-dense version they fail to fully compensate for this difference. Instead, they tend to consume a similar volume of food irrespective of its energy density (Bell, Roe, & Rolls, 2003). This observation is important because it suggests that satiation is Appetite 55 (2010) 25–29 ARTICLE INFO Article history: Received 3 November 2009 Received in revised form 2 March 2010 Accepted 7 March 2010 Keywords: Portion size Expected satiation Associative learning Perceived volume Energy intake Variance partitioning Energy density Expected satiety ABSTRACT Self-selected meals tend to be consumed in their entirety. Nevertheless, relatively little is known about the cognition associated with meal planning. Previously, we have shown that expected satiation is an excellent predictor of the energy content of self-selected meals. In the present study we sought to quantify the extent to which this relationship is mediated by differences in the perceived volume of foods (compared calorie-for-calorie). Testing took place at lunchtime. For nine highly familiar foods, participants (N = 60) selected a momentary ‘ideal’ portion, and then completed separate assessments of their expected satiation and perceived volume. Regression analysis revealed that expected satiation explained 74.8% of the variance in the energy content of self-selected meals (kcal) (p < 0.004). Of this, only 31% was shared with perceived volume, indicating that volume influences portion-size decisions by moderating expectations around satiation. However, a larger proportion of the variance (43.8%) can be considered ‘unique’ and independent of the perceived physical dimensions of the foods. We suspect that this contribution reflects the effect of prior learning, based on actual satiation that has been experienced in the past. ß 2010 Elsevier Ltd. All rights reserved. § This work was supported by a grant from the BBSRC DRINC initiative (reference BB/G005443/1). * Corresponding author. E-mail address: Jeff.Brunstrom@Bristol.ac.uk (J.M. Brunstrom). Contents lists available at ScienceDirect Appetite journal homepage: www.elsevier.com/locate/appet 0195-6663/$ – see front matter ß 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.appet.2010.03.005