Portion-size anchors as behavioural nudges of healthy eating: Testing their usefulness and limits in home settings

Purpose
Perceptions of appropriate portion sizes are socially and culturally constructed. Meals consumed at home are often linked to greater self-regulation, as individuals typically have more control over ingredients, preparation and serving sizes. However, increasing exposure to larger portions in out-of-home food environment such as restaurants and fast-food outlets risk recalibrating portion norms.
Design/methodology/approach
This study examined how low, medium and high portion-size anchors are associated with consumption intentions at home across five common foods, using a between-subjects survey experiment with 508 adult Taiwanese participants. They reported whether they would exceed the anchor and provided intended consumption amounts. Chi-square tests, Kruskal–Wallis tests and ANCOVA were used to assess anchor effects.
Findings
The direction of the anchoring effect aligns with expectations derived from the anchor-and-adjustment framework. For most food items, individuals who received the low anchor reported higher intended consumption, suggesting upward adjustment from the initial numerical cue. Conversely, those in the high anchor condition reported lower intended consumption relative to the anchor value, indicative of downward adjustment. This bidirectional movement implies that the anchor operates less as a target and more as a cognitive starting point, from which participants adjust in a context-dependent manner.
Originality
The novelty of this study lies in its examination of how portion-size anchoring effects operate within home-eating contexts in a non-Western setting.
Practical implications
Portion-size anchors offer potential for low-intensity interventions to reduce overconsumption. However, their effectiveness appears contingent on perceived plausibility. Anchors that diverge markedly from prevailing portion norms may elicit counterproductive responses.