Olfactory influences on appetite and satiety in humans.

Odor stimuli play a major role in perception of food flavor. Food-related odors have also been shown to increase rated appetite, and induce salivation and release of gastric acid and insulin. However, our ability to identify an odor as food-related, and our liking for food-related odors, are both learned responses. In conditioning studies, repeated experience of odors with sweet and sour tastes result in enhanced ratings of sensory quality of the paired taste for the odor on its own. More recent studies also report increased pleasantness ratings for odors paired with sucrose for participants who like sweet tastes, and conversely decreased liking and increased bitterness for quinine-paired odors. When odors were experienced in combination with sucrose when hungry, liking was not increased if tested sated, suggesting that expression of acquired liking for odors depends on current motivational state. Other studies report sensory-specific satiety is seen with food-related odors. Overall, these studies suggest that once an odor is experienced in a food-related context, that odor acquires the ability to modify both preparatory and satiety-related components of ingestion.