[3][4] They argue that within-meal events (immediate post-ingestive feedback, e.g., gastric stretch) play a relatively minor role and that meal size is largely determined by decisions about portion size, before a meal begins.
Consistent with this proposition, observational studies show that 'plate cleaning' is extremely common,[5] that humans tend to plan their meal size in advance, and that ad libitum eating is relatively rare.
[8][9] More recently, techniques have been developed that quantify expectations very precisely by comparing foods directly on a calorie-for-calorie basis.
This relates to the number of calories of the comparison food that would be expected to deliver the same satiety as the fixed standard.
Using specialist software, participants change the size of the comparison portion using keyboard responses.
Several studies show that these expectations also influence the hunger (physiology) and fullness that is experienced after a meal has been consumed.
Together, these observations are consistent with emerging evidence that implicates hippocampal-dependent memory mechanisms in behavioural responses to food.