Healthiness or calories? Side biases in food perception and preference

The visual perception of a product and the ability to categorize it play a central role in food choice. People's opinion of the healthiness and caloric content of a food is influenced substantially by its appearance. Despite that, few studies have analyzed i) which one of the two dimensions of caloric content and healthiness is preferred to categorize food, ii) if these dimensions are mapped on the individuals' horizontal space, and iii) if such biases could influence food preferences. Therefore, through 4 experiments, we investigated which dimension, healthiness or caloric content, is more often used to categorize foods. We also evaluated whether a healthiness/caloric content side bias could be able to influence food preferences. We found that foods were mainly categorized as "Healthy" or "High-calorie" and the latter label was used more often when presented on the right of a foodstuff. Also, foods were categorized as healthier when the "Healthy" label was anchored to the left and the "Unhealthy" one to the right side of a visual analogue scale. Then, we found a more positive evaluation of transformed food when the key assigned to the "Pleasant" choice was on the right compared to the left. Lastly, we found that when presented on the left side, low-calorie was preferred compared to high-calorie food. Our findings shed light on both the fields of food categorization and side biases in food perception and preferences, suggesting the possibility to use these biases to promote a healthy diet and emphasizing the importance of considering this potential confounder in experimental setups.