Obesity has been increasingly recognized as a major threat to global public health, and its severity continues to be underscored. Simultaneously, with the rapid rise in the elderly population and cancer patients, malnutrition resulting from appetite l...
Obesity has been increasingly recognized as a major threat to global public health, and its severity continues to be underscored. Simultaneously, with the rapid rise in the elderly population and cancer patients, malnutrition resulting from appetite loss is also becoming a significant health concern. As worries over the consequences of both obesity and appetite loss intensify, the need for effective appetite regulation strategies encompassing both appetite suppression and stimulation is growing.
Pre-ingestive sensory cues related to food are known to affect appetite and food intake, and numerous studies have verified their impact. However, most of these studies have focused solely on the effect of the stimulus itself, without sufficiently examining the influence of other factors such as exposure level, taste type, and sensory modality. In particular, prior research has primarily explored sweetness and saltiness or focused on specific food items, with relatively limited attention to other taste stimuli, such as sourness. Given that sourness can positively affect appetite by promoting salivation and swallowing and is a key characteristic of plant-based foods known to help prevent obesity, a more in-depth exploration of sour stimuli is needed. Moreover, although the effects of visual and olfactory stimuli have been widely studied, few studies have directly compared their effect on appetite under the same experimental conditions. Additionally, previous studies suggest that individual characteristics, such as BMI, eating behavior, and consumption frequency of stimulus, may significantly influence appetite and liking responses, highlighting the need for examining their moderating effects.
This study aimed to investigate how food wanting and liking, general appetite, and cravings for five sensory categories (sweetness, sourness, saltiness, bitterness, and spiciness) change in response to sweet and sour cues provided in both visual and olfactory formats. Besides the effects of exposure level, taste type, and sensory modality of cues on appetite and liking responses, the moderating roles of BMI, eating behavior patterns, and stimulus consumption frequency were investigated to obtain a comprehensive understanding of the relationship between food-related cues and food intake.
A total of 234 participants were randomly assigned to one of three groups exposed to neutral(water, n=81), sweet(chocolate milk, n=76), or sour(lemonade, n=77) cues. Within each group, participants were repeatedly exposed to both visual(food image) and olfactory(aroma) cues in a randomized, counterbalanced design with a one-week interval.
The experiment proceeded in the following order: pre-stimulus assessment, stimulus exposure and assessment, and post-experiment survey. Before exposure, hunger and thirst were measured using visual analogue scales (VAS). Liking of the stimulus, general appetite, and cravings for the five sensory categories were assessed before and after exposure using 10 cm VAS. Wanting for stimulus was measured by asking to rate how many sips participants would like to consume on an 11-point category scale (0 sip to 10 sips).
Each visual or olfactory cue was presented eight times. At each exposure, wanting for and liking of stimulus, general appetite, and cravings for specific sensations were measured. In the olfactory condition, the perceived odor intensity was assessed using the generalized Labeled Magnitude Scale (g-LMS) to monitor olfactory adaption and participants were asked to freely write two beverages the aroma reminded them of. After assessments of appetite and liking, information about participants’ demographic information, consumption frequency of stimulus, expected sensory attributes, and eating behavior were collected. Eating behavior was assessed using the TFEQ-R18, a revised version of the original Three-Factor Eating Questionnaire.
Repeated-measures ANOVA was used to analyze the effects of exposure repetition, taste type, sensory modality, and individual characteristics (BMI, eating behavior type, consumption frequency) on various appetite and liking variables. Additionally, the effects of cue characteristics (taste type and sensory modality) on the degree of changes in both the early phase (baseline-Exposure 1) and the later phase (Exposure 1-Exposure 8) were analyzed separately using repeated-measures ANOVA. The significance of each change was confirmed with one-sample t-tests by testing if the change was significantly greater than 0. Eating behavior types were identified via k-means clustering using normalized scores from the result of TFEQ-R18, resulting in three distinct groups.
Significant changes across repeated presentation of stimuli were observed in most appetite and liking variables, except for craving for bitterness. Wanting for and liking of stimulus initially increased significantly in the sweetness and sourness groups, followed by a gradual decrease with repeated exposure, particularly under visual conditions. These findings suggest that food-related cues associated with sweetness or sourness can modulate appetite and liking, and that varying levels of exposure may lead to different responses. General appetite initially increased in response to both sweet and sour cues and then stabilized, whereas the water stimulus led to an initial increase followed by a subsequent decline. This suggests that cues with distinctive taste profiles may buffer against reduction of general appetite even when stimulus-specific appetite decreases.
Sweetness craving increased after initial exposure to sweet and sour cues but declined with repetition. A similar trend was observed for sourness craving, but only with the sour cue. These findings support the potential transfer effects, whereby specific food stimuli influence appetite for other foods sharing the same sensory attributes. In contrast, craving for saltiness decreased markedly from the beginning regardless of stimulus type, with a particularly pronounced decline under visual conditions in the later phase. Craving for bitterness did not significantly change during the exposures but showed significant differences between taste conditions in the later phase. Repeated exposure to sweet cues increased craving for bitterness, whereas sour stimuli led to a slight decrease. Similarly, craving for spiciness showed differences between taste conditions in the later phase of repeated exposure, with a non-significant, slight increase by sweet cues and a significant decrease by sour cues. These results indicate that stimuli associated with specific tastes may influence other unexposed tastes or trigeminal sensations, although such effects vary depending on taste type.
Among individual traits, BMI showed a limited effect, with no meaningful differences between BMI groups observed. However, eating behavior types affected some responses. Emotional eating group showed the highest cravings for saltiness, bitterness, and spiciness, while uncontrolled eating group reported the highest liking of sweet stimulus among different eating behavior groups. Additionally, general appetite increased most in the restrained eaters during the initial phase. This may suggest that the provided cues disrupted their typical restraint mechanisms, temporarily increasing craving.
Frequent users of the stimuli tended to report higher average values of wanting for and liking of the stimulus than infrequent users. However, infrequent users displayed greater stimulus responsiveness, exhibiting more pronounced changes in both the initial increase and the subsequent decrease. These findings may point to a possible dishabituation effect, where novel stimuli elicit stronger responses than familiar ones.
This study comprehensively compared how food-related cues affect various appetite and liking responses depending on exposure level, taste type and sensory modality of cues, and individual differences. This integrative approach enhances our understanding of how pre-ingestive sensory cues influence food intake. This finding also offers meaningful insights for developing more effective and tailored dietary intervention strategies.