Red means “Green light, go for it!” Green means: “hmm, better not!” Like an upside down traffic light in our brain, color helps us decide whether or not to eat something. This, according to a study at the International School for Advanced Studies (SISSA) in Trieste and recently published in the journal Scientific Reports stating that vision is the main sense we use to guide us in food choices. To evaluate calorie intake, we rely on a “color code.”
Non-human primates evaluate food quality based on brightness of red and green shades of color, with red signaling higher energy or greater protein content in fruits and leafs. Despite the strong association between food and other sensory modalities, humans, too, estimate critical food features, such as calorie content, from vision. Previous research primarily focused on the effects of color on taste/flavor identification and intensity judgments.
However, whether evaluation of perceived calorie content and arousal in humans are biased by color has received comparatively less attention. In this study we showed that color content of food images predicts arousal and perceived calorie content reported when viewing food even when confounding variables were controlled for. Specifically, arousal positively co-varied with red-brightness, while green-brightness was negatively associated with arousal and perceived calorie content.
This result holds for a large array of food comprising of natural food – where color likely predicts calorie content – and of transformed food where, instead, color is poorly diagnostic of energy content. Importantly, this pattern does not emerged with nonfood items. We conclude that in humans visual inspection of food is central to its evaluation and seems to partially engage the same basic system as non-human primates.
Gould and Lewontin argued that, like the spandrels of St. Mark’s cathedral in Venice, some features of organisms are shaped by architectural constraints, i.e., a given biological trait is not just the result of adaptive evolution, but is constrained by its phylogenetic origin. Likewise, trichromatic vision may have evolved in response to selective pressure, but it constrains food perception even now that its selective advantage has decreased. Further evidence on how humans estimate the arousal and the calorie content of food supported by the physiological measurement of arousal together with the inclusion of liking ratings for target food will contribute to understand the mechanisms of eating behavior, enabling manipulation of visual properties of food to affect decision-making in eating behavior.