Smell it select it! Behavioral and cognitive investigations into odors influence on healthy food choices

Odors play a significant role in shaping food perception and anticipation, and may thereby promote healthier food choices. This thesis investigated two main questions:

1. Can food odors influence food choices in both laboratory and real-life settings?

2. What are the cognitive mechanisms through which food odors influence food-related decision-making?

Four studies were conducted in both real-life and laboratory contexts, employing methods such as questionnaires, food choice tasks, eye-tracking, and neuroimaging.

Chapter 2 examined whether exposure to healthy food odors influenced real-life food choices. Exposure increased purchases of healthier items (Nutri-Score A) and reduced purchases of less healthy ones (Nutri-Score D), indicating effects that were modest and context-dependent.

Chapters 3–5 examined underlying cognitive mechanisms. Chapter 3 employed a lexical decision task to examine whether odors prime food-related semantic concepts and thereby influence subsequent choices. Participants responded more slowly to non-words than to real words, and more slowly to healthy- and sensory-related words than to neutral words. However, odor exposure had no effect on reaction times or food choices, providing no evidence for semantic priming. In the subsequent choice task, participants consistently preferred unhealthy foods, irrespective of odor condition.

Chapter 4 investigated whether exposure to sweet food odors influences visual attention during food choice using a wearable eye-tracker. Healthy food products were chosen more frequently, regardless of the type of odor exposure. Furthermore, during healthy odor exposure, participants fixated longer and more frequently on food items and exhibited a longer time to first fixation, compared to the unhealthy odor condition. These findings show that healthy odors can influence early cognitive processes, but do not necessarily result in congruent food choices, suggesting other cognitive factors are involved.

Chapter 5 used functional neuroimaging (fMRI) to investigate how odor exposure affects brain activity during food-related decision-making. Behaviorally, participants chose healthy-congruent foods more often and more quickly. Neurally, food decision-making consistently engaged the dorsolateral prefrontal cortex (dlPFC) and ventrolateral prefrontal cortex (vlPFC). In addition, following healthy odor exposure, increased activation was observed in the inferior frontal gyrus (IFG) during food choices, a region linked to response inhibition, compared to the non-food odor condition. In contrast, unhealthy odors elicited greater activation in the cerebellar Crus II relative to both the healthy and non-food odor conditions, as well as increased activation in the superior frontal gyrus (SFG) compared specifically to the healthy odor. These regions are associated with reward-related processing. These findings suggest that food odors may influence food choices by engaging distinct neural systems during decision-making.

Chapter 6 integrates the findings, concluding that food odors can promote healthier choices, although the effects were modest and inconsistent across tasks. No evidence was found for semantic priming, and attention shifts did not reliably alter food selection. The effectiveness of olfactory cues likely depends on odor characteristics, task demands, and how individuals perceive and evaluate the odors. Further research should clarify these boundary conditions, delineate the different steps in cognitive processing, and explore how olfactory cues can be applied in real-world contexts to promote healthier eating.