Dissociating Accuracy and Metacognition in Nutritional Judgements

The gap between nutritional knowledge and dietary behaviour remains poorly understood, yet may partly reflect systematic biases in how individuals evaluate food and assess their own nutritional judgements. Here, we introduce the MetaBites task, a novel two-alternative forced-choice paradigm in which 32 healthy volunteers compared foods on either caloric density or nutritional quality, quantified using the Nutrient-Rich Foods (NRF) 9.3 index, under adaptive difficulty control. Participants provided both trial-level and block-level confidence ratings, enabling assessment of metacognitive monitoring across multiple levels. Task validity was confirmed through staircase convergence, a clear speed-accuracy trade-off, and higher confidence in correct relative to incorrect trials. Results revealed a consistent dissociation across conditions: participants showed higher objective performance when judging nutritional quality, yet reported significantly higher confidence and greater metacognitive efficiency for calorie judgements. Global confidence decreased significantly in the NRF condition but remained stable for calorie judgements. Furthermore, familiarity with food items biased choice behaviour in opposing directions across conditions, consistent with a tendency to perceive familiar foods as more nutritious and less calorie-dense. These findings indicate that metacognitive monitoring in nutritional judgements is not a straightforward readout of objective performance, and that domain familiarity modulates choice behaviour. The MetaBites task offers a promising tool for investigating metacognitive contributions to nutritional decision-making in both healthy and clinical populations.