The problem of large portion sizes: a norm-comparison theory explaining the psychological influence and public health implications of food portion size

Abstract

Portion size of food has a causal influence on human energy intake and historic increases in commercial food product portion sizes are suggested to have contributed to population-level obesity. A norm-comparison theory explains the influence of food portion size and suggests that increasing portion sizes are problematic for two reasons. First, this norm-comparison theory explains why changes to food portion size can have a sizeable influence on energy intake during a meal without inviting later compensatory eating behaviour. Second, because there is no objectively 'correct' portion size for any given food, exposure to larger portion sizes recalibrates perceptions of what a normal amount to eat is for any given food. Over time this process will have caused preferred portion sizes to shift upwards and contributed to increases in population level energy intake. However, a norm-comparison theory of food portion size also has implications for how to address the problem of excessively large portion sizes and guide public health measures to decrease population energy intake and body weight.

Keywords: Norm-comparison; Obesity; Perception; Portion size; Public health.