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Olfactory influences on appetite and satiety in humans
Abstract
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.
... (1-3 minutes) to the food cues (e.g., Cornell et al., 1989;Ferriday & Brunstrom, 2011;Yeomans, 2006). In contrast, a few studies have observed SSA in longer exposure conditions. ...
... Recently, researchers argue that aroma and taste cues present in food during consumption can facilitate compensatory effects and determine subsequent food choice and intake, despite simply regulating the amount eaten and satiation (e.g., Small et al., 2005;Yeomans, 2006). ...
... Overall, previous studies highlighted the importance of assessing the effects of olfactory and gustatory cues (exposure) on subsequent snack intake. Specifically, with the importance of considering olfactory and gustatory cues present during the consumption (e.g., Small et al., 2005;Yeomans, 2006), this study used real foods as delivery systems to test for sweetassociated aroma (vanillin) and taste (sucralose) induced sensory-specific effects in natural settings. The choice of the above aroma and taste cues is due to the promising links between ...
Obesity has become a critical health issue in many developed countries, including New Zealand. While the aetiology of obesity is likely to be multifactorial, overconsumption is deemed as a key behavioural contributor to the growing obesity rate. Emerging sensory nutritional research has proposed that obesity is linked to altered olfactory and gustatory sensitivities, which can in turn influence consumption, particularly of foods rich in sugar, salt, and fats. Despite being promising, empirical studies to test for this hypothesis have returned highly controversial results. The present doctoral thesis aims to ‘systematically evaluate the role of olfaction and gustation in regulating an individual’s adiposity and eating behaviour’, using well-validated psychophysical, nutritional, and food-psychological approach.
The present thesis firstly aimed to develop and test for new approaches to quantify individual chemosensory sensitivities to food-related stimuli, based on assessments of individual performance to decremental (d′(d)) and incremental (d′(i)) stimulus range. Subsequently, these sensitivity measures were analysed against inter-individual differences in adiposity measures and eating behaviour. Additional exploratory research was performed to further analyse possible factors driving chemosensory links to food-related behaviour. Two separate datasets were collected in this thesis, with Data Collection 1 involving N=70 (age range = 21-39 years, BMI range = 20.5-48.1 kg·m-2) and Data Collection 2 involving N=61 (age range = 21-39 years, BMI range = 19.7-41.5 kg·m-2) participants.
The results from the first analysis show that individuals’ sensitivities to decremental stimulus range (d′(d)) and to incremental stimulus range (d′(i)) represent distinct measures. Furthermore, the measure of d′(d) is positively associated with adiposity measures, whereas d′(i) exhibits a negative relationship. Furthermore, these two separate sensitivity measures had significant, but contradictory, relationships with snack intake and total habitual energy intake. Specifically, individuals with poor olfactory and gustatory sensitivities (high d′(d) and low d′(i)) appeared to consume more sweet versus savoury snacks, than their counterparts, pointing to an important differentiating role of snack consumption.
In the context of the aforementioned findings, the last study of the thesis tested whether exposure to olfactory and gustatory cues in a meal influences subsequent snack choice and intake. With a repeated-subject design over one control and four testing sessions, the participants had breakfasts with manipulated olfactory and gustatory characteristics and recorded their snack intake throughout the day. Results from this study revealed that high-intensity olfactory and gustatory characteristics of a meal reduce sweet snack intake and increase the non-sweet snack intake, while total snack intake is maintained across the sessions. Specifically, individuals with high gustatory sensitivity showed more sensory-specific effects compared to the low-sensitivity group. Moreover, the high-BMI group showed sensory-specific effects for low- and high-intensity sweet taste cues, in contrast, the low-BMI group showed sensory-specific effects only for the high-intensity taste cues. Overall, the findings of this specific study highlight that the olfactory and gustatory cues of a meal may have a day-long effect on snack choice, providing novel insights into the observed association between sensory sensitivity and adiposity.
Overall, this doctoral thesis systematically assessed the role of individual olfactory and gustatory sensitivities in influencing adiposity and eating behaviour. With multifactorial data ranging across sensory science, nutrition and food psychology, this thesis provides new insights into inter and intra-individual differences in olfactory and gustatory sensitivities, and their important links to eating behaviour.
... Orthonasal smell drives food acceptance as it occurs prior to consumption, thereby setting our expectations of food palatability (Spence, 2015), modulating appetite (Yeomans, 2006, Yin et al., 2017 and stimulating physiological response (such as salivary flow) in preparedness for food digestion (Spence, 2015). To promote appetite Factors affecting adherence, intake, and perceived palatability of ONS: A literature review 77 and nutritional intake, positive orthonasal cues are crucial for older individuals that are already experiencing blunted appetite sensations (Section 2.3.3.2). ...
... Retronasal olfaction refers to the release of volatile aromas from foods, which travel through the gaseous airspace, and bind with olfactory receptors in the back of the nose during food consumption. It is retronasal olfaction that combines with the perception of taste and trigeminal stimuli to drive the perception of food flavour, and hence the palatability of food (Yeomans, 2006). ...
... The orthonasal evaluation of food aroma plays a vital role in identifying the suitability of a food item for consumption and communicates to the consumer about the palatability and nutritional adequacy of food before it is placed in the mouth (Stevenson, 2010). Furthermore, positive aroma can stimulate salivation, promote appetite and increase food intake (Spence, 2015, Yeomans, 2006. Our findings hypothesise that these high-impact, unpleasant sulfurous aromas contribute to the poor reported orthonasal aroma quality of ONS (Lad et al., 2005, Lambert et al., 2017. ...
Within the increasing older population, there is a burden of undernutrition. The prescription of oral nutritional supplements (ONS) for those who are undernourished, or at risk of undernutrition, can help improve nutritional status, but the patient must consume an adequate quantity of ONS to gain the clinical benefits. This research first reviewed the literature to identify factors that influence adherence to ONS. Good palatability is crucial for adequate intake of ONS, but palatability challenges stem from both the product (undesirable sensory properties) and the consumer (age-related sensory changes). The contribution made by aroma compounds to the palatability of ONS was recognised as a comparatively underresearched area. Therefore, this work aimed to fill the evidence gap by investigating the role of intrinsic flavour quality (with emphasis on aroma) and age-related changes in oronasal physiology and sensory abilities on sensory perception and palatability of ONS. The characterisation of aroma-active compounds in a commonly prescribed ONS was a fundamental stage in the research. Esters (sweet, fruity) and diacetyl (sweet, buttery) were found to make a large contribution to the perceived flavour of the studied ONS. Sulfurous aroma compounds, likely stemming from the heat-treatment of protein ingredients, were also found to contribute to the perceived flavour of ONS. An orthonasal hedonic evaluation established that sulfurous aroma compounds are primarily unpleasant, whereas the fruity ester aroma (isoamyl acetate) and diacetyl are primarily pleasant. However, sulfurous aromas were rated more pleasantly by older adults who also had impairments in their ability to detect aromas at threshold concentrations. When aromas were combined in a mixture within a real-food matrix (a flavoured dairy beverage), sulfurous aroma compounds were shown to negatively impact consumer acceptance (for consumers aged 18 – 79 years). However, these sulfurous flavours were less objectionable for older adults. This is a novel finding because it suggests that olfactory impairments may benefit older consumers who need to consume protein-rich foods containing off-flavours. Furthermore, the addition of diacetyl increased the acceptability of the sulfurous flavours, demonstrating partial masking abilities of this compound. Older adults are also known to experience age-related changes in their oral and nasal physiology, such as reduced salivary flow rates which may influence the way flavours are released in the mouth. Therefore, the next stage of the research investigated differences in the temporal consumption experience (comprising in-mouth aroma release, sensory perception and subjective appetite) of a clinically relevant portion of ONS for groups differing in saliva flow rate, in which repeated measurements were made between sips. This study demonstrated that a lower saliva flow rate is associated with significantly more intense in-mouth aroma release (p=0.015), significantly higher aftertaste intensity (p<0.001), and greater increase in mouth drying over sips (p=0.02), compared to a medium- and high- saliva flow rate. These findings occurred concurrently with relatively lower hunger sensations in the low- and medium-flow rate groups. This research adds to the growing body of evidence on how best to optimise food and beverage palatability for older consumers. Many older patients who are prescribed ONS are likely to experience reduced salivary flow rates and olfactory impairments. The unique sensory experience of these individuals should be considered in both product development and clinical practice to optimise palatability, hence maximising nutritional intake from ONS and other nutritional foods and beverages whilst minimising wastage.
... One that is presented together with a taste, and another one that is presented alone (or with a different taste, e.g. Yeomans 2006;Stevenson & Mahmut 2011a). Changes in perceptual and hedonic features can then be compared between the odors to isolate effects of associative learning from effects that might have been caused by exposure to the odor alone. ...
... Changes in perceptual and hedonic features can then be compared between the odors to isolate effects of associative learning from effects that might have been caused by exposure to the odor alone. Distinguishing between these two learning processes is particularly important when studying pleasantness, as previous work has suggested that the hedonic tone of odors can be influenced both by exposure to pure odors (Delplanque et al. 2015) and by exposure to odors together with sweet taste (Yeomans et al. 2006). While there is no reason to expect that odors will become sweeter due to exposure alone, the inclusion of an odor presented without taste allows one to test if the increase in odor sweetness will be greater for sweet-paired than for unpaired odors. ...
... These conflicting results may be explained by interindividual differences in taste preferences. This notion has gained support from a study where odor pleasantness indeed increased more after exposure with sucrose than after exposure without taste, but only for participants that liked sweet taste to begin with (Yeomans, 2006). Evidence so far thus indicates that sweet-liking is a necessary prerequisite for associative learning when it comes to odor pleasantness. ...
Repeated exposure can change the perceptual and hedonic features of flavor. Associative learning during which a flavor’s odor component is affected by co-exposure with taste is thought to be central in this process. However, changes can also arise due to exposure to the odor in itself. The aim of this study was to dissociate effects of associative learning from effects of exposure without taste by repeatedly presenting one odor together with sucrose and a second odor alone. Sixty individuals attended two testing sessions separated by a five-day exposure phase during which the stimuli were presented as flavorants in chewing gums that were chewed three times daily. Ratings of odor sweetness, odor pleasantness, odor intensity enhancement by taste, and odor referral to the mouth were collected at both sessions. Consistent with the notion that food preferences are modulated by exposure, odor pleasantness increased between the sessions independently of whether the odor (basil or orange flower) had been presented with or without sucrose. However, we found no evidence of associative learning in any of the tasks. In addition, exploratory equivalence tests suggested that these effects were either absent or insignificant in magnitude. Taken together, our results suggest that the hypothesized effects of associative learning are either smaller than previously thought or highly dependent on the experimental setting. Future studies are needed to evaluate the relative support for these explanations and, if experimental conditions can be identified that reliably produce such effects, to identify factors that regulate the formation of new odor-taste associations.
... The importance of the sense of smell in everyday life and evolution is quite clear [1]. From its hedonistic aspect of life and eating satisfaction to its survival aspect, which involves detecting danger in the environment or toxins and edibility of food, all indicate the importance of having intact olfactory sensation [2,3]. The olfactory pathway and network in primates can be traced back to the primary regions including olfactory bulb to the entorhinal and piriform cortices of the temporal lobes, and also to the thalamus, hypothalamus, and parts of the limbic system [4]. ...
... While finding precise methodologies for the early diagnosis of these diseases and other sensory modalities are of great interest to the researchers, olfactory system of the brain is still understudied [2,3,4,5]. ...
Purpose: Olfactory system is a vital sensory system in mammals, giving them the ability to connect with their environment. Anosmia, or the complete loss of olfaction ability, which could be caused by injuries, is an interesting topic for inspectors with the aim of diagnosing patients. Sniffing test is currently utilized to examine if an individual is suffering from anosmia; however, functional Magnetic Resonance Imaging (fMRI) provides unique information about the structure and function of the different areas of the human brain, and therefore this noninvasive method could be used as a tool to locate the olfactory-related regions of the brain. Materials and Methods: In this study, by recruiting 31 healthy and anosmic individuals, we investigated the neural Blood Oxygenation Level Dependent (BOLD) responses in the olfactory cortices following two odor stimuli, rose and eucalyptus, by using a 3T MR scanner. Results: Comparing the two groups, we observed a network of brain areas being more active in normal individuals when smelling the odors. In addition, a number of brain areas also showed an activation decline during the odor stimuli, which is hypothesized as a resource allocation deactivation. Conclusion: This study illustrated alterations in the brain activity between normal individuals and anosmic patients when smelling odors, and could potentially help for a better anosmia diagnosis in the future.
... FAT aldehydes from α-linolenic acid (ALA) 12. Impact of FAT aldehyde olfaction on human living 13. A prospect on the detection and discrimination of long-chain fatty acids in the nasal cavity of humans the significance of pre-perceiving the nutritional value and safety of foods should not be overlooked (Yeomans 2006;Stevenson 2010;McCrickerd and Forde 2016;Kindleysides et al. 2017). The olfactory sensing of nutrients, including fats, may be particularly important for newborns who cannot make visual and habitual dietary choices (Marlier and Schaal 2005;Loos et al. 2019;Klaey-Tassone et al. 2021). ...
... Although the palatability of food depends on various factors, including vision, taste, mouth feel, and temperature, the contribution of odor cannot be neglected (Yackinous and Guinard 2000;Yeomans 2006;McCrickerd and Forde 2016). For instance, the odors produced by heating LA-dominant edible oils, such as sunflower oil (Ewert et al. 2011;Thürer and Granvogl 2016;Rabail et al. 2021), play a sig-such as octanal (C8) and nonanal (C9), which was accelerated by heating [note that triolein heating also did so (Selke et al. 1997)]. ...
Fat (triglycerides) consumption is critical for the survival of animals, including humans. Being able to smell fat can be advantageous in judging food value. However, fat has poor volatility; thus, olfaction of fat seems impossible. What about fatty acids that comprise fat? Humans smell and discriminate medium-chain fatty acids. However, no conclusive evidence has been provided for the olfactory sense of long-chain fatty acids, including essential acids such as linoleic acid (LA). Instead, humans likely perceive the presence of essential fatty acids through the olfaction of volatile compounds generated by their oxidative breakdown (e.g., hexanal and γ-decalactone). For some people, such scents are pleasing, especially when they come from fruit. Nonetheless, it remains unclear whether the olfaction of these volatiles leads to the recognition of fat per se. Nowadays, people often smell LA-borne aldehydes such as E,E-2,4-decadienal that occur appreciably, for example, from edible oils during deep frying, and are pronely captivated by their characteristic “fatty” note, which can be considered a “pseudo-perception” of fat. However, our preference for such LA-borne aldehyde odors may be a potential cause behind the modern overdose of n-6 fatty acids. This review aims to provide a view of whether and, if any, how we olfactorily perceive dietary fats and raises future purposes related to human fat olfaction, such as investigating sub-olfactory systems for detecting long-chain fatty acids.
... Odor stimuli play an important role in the perception of ingested food flavor. Food-related odors have been shown to induce appetite, salivation, gastric acid, and insulin secretion (11). Olfaction stimulates salivary secretions (12). ...
... Odor stimuli play a major role in the perception of food flavor, appetite, salivation, and release of enzyme and hormone secretion to the metabolism of foods (11). Olfactory bulb lesions lead to substantia nigra degeneration, mammary gland insults, Peyer's patches hyperplasia induced by infections, hypothyroidism, neuropsychiatric disorders, sexual problems, Hirschprung-like disease, and spermatogenesis disorders (10,(30)(31)(32)(33)(34)(35). ...
Aim: Dry mouth has been considered a clinical finding of Parkinson’s disease (PD), but we think otherwise. We studied if the olfactory bulbectomy (OBX) might rely on the superior salivatory nucleus (SSN), submandibular ganglia (SMGn), and submandibular glands (SLGl) circuity disruption induced submandibular gland degeneration related dry mouth in rats. Material and Method: This study was carried out on twenty-six male rats. Five (GI-n=5), six (GII, n=6), and sixteen (GIII, n=15) of them were used as control, SHAM, and OBX groups, respectively, and followed eight weeks. PD-related clinical examinations were done before and after the experiment (1/day), and animals were decapitated. The olfactory bulb volumes (mm3), degenerated neuron densities of SSN/SMG (n/mm3 and SMGl follicles volumes were detected serologically. Olfactory bulb volume values and degenerated neuron density values of SSN/SMGn/SMGl follicles volumes were compared statistically. Results: OBX-applied animals showed anosmia, tremors, rigidity, and memory loss. The mean olfactory bulb volumes (mm3), degenerated neuron density of SSN (n/mm3), SMGn (n/mm3), and follicles volumes of SMGl (cubic micrometer/mm3) were measured in the order written as; (4.27±0.21), (4±1), (5±2), (81.23±13.34).106 in GI; (3.67±0.33), (14±3), (17±4), (72.45±11.78).106 in GII and (2.91±0.14), (23±5), (29±8), (57.19±11.93).106 in Group III. The mean P values between olfactory bulb volumes, degenerated neuron densities of SSN and SMGn, and salivary follicles volumes were: p
... 1,2 Although it is known that a complex neural network plays a pivotal role in individual's olfactory performance, odor-driven behaviors, and food consumption, 1,3,4 it remains still unclear how olfactory abilities are linked-vice versa-to adiposity through direct impacts on eating behavior. 5 It has been recently highlighted that the olfactory system plays as a detector not only of external chemical milieu but also of the internal chemistry of metabolism. 6 The detection and hedonic representation of food odors might be phasically burdened by hungry and satiety, thereby influencing the beginning or the end of eating behaviors. ...
... 6 The detection and hedonic representation of food odors might be phasically burdened by hungry and satiety, thereby influencing the beginning or the end of eating behaviors. 5,7 During the past decade, a myriad of metabolic cues, whose circulating levels are dependent on nutritional status (i.e., leptin, insulin, ghrelin, glucose, insulin-like growth factor-1 [IGF-1]), have been recognized to play as direct modulators of the peripheral and central neuronal stream entailed in olfactory functions (for review see 6 ). Because the olfactory system drives behavioral choices about food preference and consumption, it is well poised to be modulated by obesity when there is a derangement in glucose and insulin utilization, which-among other energy important molecules-are detected by the olfactory bulb (OB). ...
Objective:
To evaluate the differences in olfactory sensitivity, nutritional habits, levels of modulators of feeding and smell, bioelectrical impedance analysis (BIA) measures and metabolic assays between two groups of participants with stage I and II obesity and reciprocal relationships between these parameters.
Methods:
Eighteen participants with stage I (11 female; mean age = 54.3 ± 13.1 years) and 20 participants with stage II (10 female; mean age = 54.5 ± 11.9) obesity underwent a food frequency questionnaire and Sniffin' Sticks® test battery, anthropometric parameters, and BIA measurements as well as metabolic assays (including plasma levels of leptin, insulin, ghrelin, glucose, insulin-like growth factor-1 [IGF-1] and usual laboratory parameters).
Results:
The stage II obesity participants demonstrated significant higher levels of insulin and leptin and lower levels of ghrelin and IGF-1, a reduction in odor identification (OI) and in total olfactory score, and an increase in visceral and total fat percentage. Among a mosaic of multiple correlations, ghrelin was found to positively correlate with OI and leptin negatively with odor discrimination.
Conclusion:
The present study expands the notions positing the olfactory perception - and its connections with metabolic cues, foods habits and BIA measures - changes across the two most important obesity stages. This could ameliorate clinical and research deepening of obesity-related olfactory behavior with possible consequences on diagnosis, treatment and prevention of onset and development of obesity, thus opening possible future strategies involving multidisciplinary contributions.
Level of evidence:
Level 3 Laryngoscope, 2022.
... In this context, smell is one of the most relevant sensory cues predicting food characteristics and is likely to play a key role in food choice and consumption (Boesveldt and de Graaf, 2017). The relation between olfaction and food intake has been established early on (Le Magnen, 2001;Yeomans, 2006) but did not receive much attention in the context of metabolic diseases until recently. ...
... Even though it is recognized in humans that smell strongly influences appetite and satiety (Yeomans, 2006), the crosstalk between olfaction, food intake and energy metabolism in physiological conditions is still largely unknown. ...
The olfactory system is at the crossroad between sensory processing and metabolic sensing. In addition to being the center of detection and identification of food odors, it is a sensor for most of the hormones and nutrients responsible for feeding behavior regulation. The consequences of modifications in body homeostasis, nutrient overload and alteration of this brain network in the pathological condition of food-induced obesity and type 2 diabetes are still not elucidated. The aim of this review was first to use both humans and animal studies to report on the current knowledge of the consequences of obesity and type 2 diabetes on odorant threshold and olfactory perception including identification discrimination and memory. We then discuss how olfactory processing can be modified by an alteration of the metabolic homeostasis of the organism and available elements on pharmacological treatments that regulate olfaction. We focus on data within the olfactory system but also on the interactions between the olfactory system and other brain networks impacted by metabolic diseases.
... The importance of the sense of smell in everyday life and evolution is quite clear [1]. From its hedonistic aspect of life and eating satisfaction to its survival aspect, which involves detecting danger in the environment or toxins and edibility of food, all indicate the importance of having intact olfactory sensation [2,3]. The olfactory pathway and network in primates can be traced back to the primary regions including olfactory bulb to the entorhinal and piriform cortices of the temporal lobes, and also to the thalamus, hypothalamus, and parts of the limbic system [4]. ...
... While finding precise methodologies for the early diagnosis of these diseases and other sensory modalities are of great interest to the researchers, olfactory system of the brain is still understudied [2,3,4,5]. ...
Olfactory system is a vital sensory system in mammals, giving them the ability to connect with their environment. Anosmia, or the complete loss of olfaction ability, which could be caused by injuries, is an interesting topic for inspectors with the aim of diagnosing patients. Sniffing test is currently utilized to examine if an individual is suffering from anosmia; however, functional Magnetic Resonance Imaging (fMRI) provides unique information about the structure and function of the different areas of the human brain, and therefore this noninvasive method could be used as a tool to locate the olfactory-related regions of the brain. In this study, by recruiting 31 healthy and anosmic individuals, we investigated the neural BOLD responses in the olfactory cortices following two odor stimuli, rose and eucalyptus, by using a 3T MR scanner. Comparing the two groups, we observed a network of brain areas being more active in the normal individuals when smelling the odors. In addition, a number of brain areas also showed an activation decline during the odor stimuli, which is hypothesized as a resource allocation deactivation. This study illustrated alterations in the brain activity between the normal individuals and anosmic patients when smelling odors, and could potentially help for a better anosmia diagnosis in the future.
... Taste is found to be significantly moderated by olfactory sensations. Yeomans (2006) argued that olfactory stimuli contribute a significant proportion of taste judgment for most foods. Besides, the ability of taste-congruent odors to influence taste judgment is a commonly reported effect in marketing and nutrition literature, and this is particularly evident in pastry research. ...
... Knowing the limitations of this approach and in line with Budescu and Weiss (1987) conclusions, we asked the participants two different sets of experimentunrelated questions before each experiment. Additionally, as recommend in previous sensory research on olfaction and taste perception (Fujimaru and Lim, 2013;Yeomans, 2006), every two experiments are separated by a time span of four days to lower the effects of any memory trace left from the previous experiment on the behavior of participants in the current experiment, and thus, minimize the demand effects. Two groups of average weight consumers between 21 and 58 years of age participated in two experiments. ...
Purpose
The purpose of this paper is to test for gender-specific effects on odor-induced taste enhancement and subsequent food consumption in olfactory food marketing.
Design/methodology/approach
Lab experiments conducted among female and male participants using vanillin as a stimulus and ratings of sweetness, taste pleasantness and eating of sugar-free food as measures.
Findings
Odor-induced taste enhancement is gender-specific. Female consumers outperform male consumers in olfactory reaction and sweetness perception. While men outperform women in food consumption.
Research limitations/implications
Odor intensity was set to the concentration level of 0.00005per cent according to the findings from (Fujimaru and Lim, 2013). The authors believe that this intensity level is appropriate for both men and women. Still, there may be some gender effects on intensity levels, which are not explored here. The author’s test for the effects of one personal factor, gender and odor-induced taste enhancement of sugar-free food. The authors think that investigating the combined effects of more personal factors such as age, culture and so on adds to the accuracy of the results.
Practical implications
It seems that the stronger sensory capacities of women in terms of odor detection and recognition already confirmed in the literature extends to the cross-modal effects of this sensory detection and recognition on taste enhancement. It seems appropriate to tailor olfactory food advertising according to the gender of the target audience.
Originality/value
Odor-induced taste enhancement is still a novel subject in marketing. While most of the research has investigated the effects of smelling congruent odors on taste perception and food consumption among mixed groups of men and women, the value of this paper lies in the investigation of the potential moderating effects of gender on this relationship.
... The olfactory system is closely related to nutritional status. Hunger could stimulate olfactory sensitivity [42], while odor induces olfactory influence on appetite and satiety [43,44]. The dietary fat intake leads to loss of olfactory sensory neurons and related circuits, which cannot be mitigated by voluntary exercise in mice [45], suggesting a potential link between obesity-related intake factors and olfactory receptors. ...
Olfactory receptors are seven-transmembrane G-protein-coupled receptors on the cell surface. Over the past few decades, evidence has been mounting that olfactory receptors are not unique to the nose and that their ectopic existence plays an integral role in extranasal diseases. Coupled with the discovery of many natural or synthetic odor-compound ligands, new roles of ecnomotopic olfactory receptors regulating blood glucose, obesity, blood pressure, and other metabolism-related diseases are emerging. Many well-known scientific journals have called for attention to extranasal functions of ecnomotopic olfactory receptors. Thus, the prospect of ecnomotopic ol-factory receptors in drug target research has been greatly underestimated. Here, we have provided an overview for the role of ecnomotopic olfactory receptors in metabolic diseases, focusing on their effects on various metabolic tissues, and discussed the possible molecular biological and pathophysiological mechanisms, which provide the basis for drug development and clinical application targeting the function of ecnomotopic olfactory receptors via literature machine learning and screening.
... Sense of smell and taste changes. Food-related odours have a role in the stimulation of appetite, and both senses of smell and taste have a significant role in making eating and drinking enjoyable (72,93) . However, sensory sensitivity to both taste and smell can decrease with age due to factors such as a reduction in the replenishment of taste and olfactory receptor cells (62,94) . ...
Globally, we are currently facing a rapid demographic shift leading to an increase in proportion of older adults within the population. This raises concerns about the potential increase in age-related diseases and their impact on our ability to provide adequate health and end-of-life care. To apply appropriate interventions, understanding the changes that happen with ageing becomes essential. Ageing is often accompanied by a decrease in appetite and physical activity, which may lead to malnutrition, resulting in decreased muscle mass, physical capabilities, and independence. To preserve muscle mass, older adults are advised to increase protein intake and physical activity. However, protein’s high satiating effect may cause reduced energy intake. Physical activity is also advised to maintain or enhance older adult’s appetite. This review paper aims to discuss appetite-related changes that occur with ageing and their consequences. In particular, it will focus on investigating the relationship between protein intake, physical activity, and their impact on appetite and energy intake in the ageing population. Recent studies suggest that physical activity might contribute to maintaining or enhancing appetite in older adults. Nevertheless, establishing a definitive consensus on the satiating effect of protein in ageing remains a work in progress, despite some promising results in the existing literature.
... The findings revealed that when participants were exposed to congruent olfactory cues (e.g., the smell of strawberries while consuming a strawberry-flavoured dessert), their perception of taste was significantly enhanced compared to incongruent or no olfactory cues. Another studies (Yeomans, 2006 andDoets andKremer et al., 2016) focused on the impact of olfactory stimulation on satiety and food consumption between seniors and younger adults. ...
In the contemporary food landscape, where easily accessible and appetizing food options prevail, the issue of overconsumption and its contribution to global obesity concerns remains a critical societal and research challenge. While it is well-established that sensory appeal plays a key role in motivating eating behaviour, recent studies have underscored the direct impact of sensory properties on food consumption, mediated by internal signals like hunger and satiety. Among the various sensory factors influencing eating behaviour, two phenomena have garnered significant scientific interest: sensory-specific satiety (SSS) and sensory-specific appetite (SSA). In this research we aim to explore if augmenting food products through visual, olfactory, and haptic feedback can change eating behaviour and affect SSA or SSS. To further expand our understanding of these phenomena, this study employs a novel system utilizing multimodal augmentation of plant and meat-based products consumed in a controlled environment.
... Partially, this knowledge gap mirrors the relative complexity of the olfactory system in mammalian [1]. While it is known that a complex neural network plays a pivotal role in individual's olfactory performance, odor-driven behaviors and food consumption [1,12], it still remains unclear how olfactory abilities are linked-viceversa-to adiposity through direct impacts on eating behavior [13]. ...
Purpose:
To evaluate the changes in gustatory and olfactory sensitivity and dietary habits between healthy lean subjects (LS) and participants affected by overweight (OW), stage I and II obesity and to estimate possible impact of these factors on body mass index (BMI).
Methods:
After a general and ear-nose-throat evaluation, taste and olfactory function testing by means of taste strips and sniffin' stick tests, respectively, and food habits analysis by means of food frequency questionnaire (FFQ), 221 participants (68 LS [33 female; mean age = 53.01 ± 7.54 years]; 51 OW [26 female; mean age = 51.5 ± 12.16 years]; 50 stage I obesity [24 female; mean age = 50.78 ± 13.71 years] and 52 stage II obesity [24 female; mean age = 52.21 ± 13.35 years]) were enrolled in the study.
Results:
Significant (p < 0.008) reductions in total and subtest taste and smell scores were found in stage I and II obesity when compared to LS and OW participants. FFQ depicted a progressive intake increase of nutrients along the BMI stages. Significant associations were found between BMI and taste/smell subtests sugar taste carbs, saturated, monounsaturated and polyunsaturated fatty acids.
Conclusions:
These data demonstrated for the first time a parallel impairment in smell and taste in a large sample size of participants from lean to stage II obesity and could reinforce those previous theories claiming that the greater the ability in taste or smell qualities perception, the lower the preference for them, resulting in a lower intake of specific foods.
... The sense of smell allows people to quickly assess food before consumption (van Stokkom et al., 2018), protecting against eating something spoiled and helping identify food ingredients. It is worth noting that while smell is crucial for taste perception (Frank & Byram, 1988), food-related odors also influence appetite (Schiffman & Graham, 2000;Yeomans, 2006). This is evidenced by increased hunger ratings and the stimulated secretion of saliva and gastric acids following exposure to food-related odors (Feldman & Richardson, 1986;Rogers & Hill, 1989). ...
... Several studies demonstrated the connectivity between olfactory brain regions and the hypothalamic regions that regulate food intake 80 . Specifically, connections between the olfactory bulb and the hypothalamic arcuate nucleus where POMC neurons are located have been described [80][81][82] . Sensory detection of food after pellet presentation to mice activated POMC neurons 83 , indicating that POMC neurons may be involved in anticipatory behavior in preparation for food intake 48 . ...
Mutations in the Fragile X Messenger Ribonucleoprotein 1 (FMR1) gene are linked to Fragile X Syndrome, the most common monogenic cause of intellectual disability and autism. People affected with mutations in FMR1 have higher incidence of obesity, but the mechanisms are largely unknown. In the current study, we determined that male Fmr1 knockout mice (KO, Fmr1−/y), but not female Fmr1−/−, exhibit increased weight when compared to wild-type controls, similarly to humans with FMR1 mutations. No differences in food or water intake were found between groups; however, male Fmr1−/y display lower locomotor activity, especially during their active phase. Moreover, Fmr1−/y have olfactory dysfunction determined by buried food test, although they exhibit increased compulsive behavior, determined by marble burying test. Since olfactory brain regions communicate with hypothalamic regions that regulate food intake, including POMC neurons that also regulate locomotion, we examined POMC neuron innervation and numbers in Fmr1−/y mice. POMC neurons express Fmrp, and POMC neurons in Fmr1−/y have higher inhibitory GABAergic synaptic inputs. Consistent with increased inhibitory innervation, POMC neurons in the Fmr1−/y mice exhibit lower activity, based on cFOS expression. Notably, Fmr1−/y mice have fewer POMC neurons than controls, specifically in the rostral arcuate nucleus, which could contribute to decreased locomotion and increased body weight. These results suggest a role for Fmr1 in the regulation of POMC neuron function and the etiology of Fmr1-linked obesity.
... • guide successful food choice (Auvray & Spence, 2008;Smith, 2015;Yeomans, 2006)? ...
Theories of perception have traditionally dismissed the sense of smell as a notoriously variable and highly subjective sense, mainly because it does not easily fit into accounts of perception based on visual experience. So far, philosophical questions about the objects of olfactory perception have started by considering the nature of olfactory experience. However, there is no philosophically neutral or agreed conception of olfactory experience: it all depends on what one thinks odors are. We examine the existing philosophical methodology for addressing our sense of smell: on the one hand appeals to phenomenology that focus on the experiential dimensions of odor perception and on the other approaches that look at odor sources and their material dimensions. We show that neither strategy provides enough information to account for the human sense of smell and argue that the inclusion of the missing dimension of biology, with its concern for the function (or functions) of olfaction, provides the means to develop a satisfactory and empirically informed philosophy of smell.
... e loss of sense of smell greatly impacts the patient's quality of life (QoL), as a result of insecurities regarding personal hygiene, lack of hazard awareness (e.g., burning smell and gas leaks), and reduced food enjoyment [3,4]. Olfactory stimuli are important food cues that can increase appetite and play an important role in flavor perception [5,6]. It has been demonstrated that exposure to olfactory stimuli results in increased food intake [7]. ...
Introduction:
Hyposmia is a frequent symptom of Parkinson's disease (PD), which greatly impacts patients' flavor perception and their quality of life. However, PD patients recognize some odors better than others. Identifying which food odors are still recognized by PD patients may be useful for flavor enhancement. Our aim was to evaluate the olfactory identification of Sniffin' Sticks and spice odorants in PD patients and healthy controls (HC), to identify the impact of synthetic odorants compared with real-life food and the impact of odor familiarity and pleasantness on odorant identification in PD patients.
Methods:
Sniffin' Sticks odorant identification was evaluated in 80 PD patients and 105 age-matched HC. In a subset, the spice odorant identification was evaluated.
Results:
The mean total score was higher for the Sniffin' Sticks than for the spice odor identification test in all participants (55.4% versus 22.5%). Sniffin' Sticks orange, peppermint, rose, and fish odorants were best correctly identified by PD patients, by 62.5, 53.8, 52.9, and 57.5%, respectively. Of the spice odor identification test, garlic and "no stimulus" were best correctly identified by PD patients, by, respectively, 38.2 and 67.6%. HC identified most Sniffin' Sticks odorants and spices better than PD patients. Odorant familiarity determined real-life food odorant identification.
Conclusion:
This study demonstrates that some food odorants, both the commercial Sniffin' Sticks as natural odorants, are still recognized by PD patients. Sniffin' Sticks were better recognized compared with real-life odorants, by both HC and PD patients. Odorant familiarity determined PD patients' odorant identification; therefore, familiar food odorants may have potential for a future flavor enhancement. Implications. This is the first study, to our knowledge, to evaluate real-life food odor identification in PD patients. Our results provide a first step towards patient-appropriate flavor enhancement strategies in PD.
... For instance, the rating of hunger is increased following exposure to food-related odors (Rogers and Hill, 1989). Food-related odors significantly stimulate salivation, insulin release, and gastric acid secretion (Yeomans, 2006). Food odorants also drive animals to consume more food (Reisenman and Scott, 2019). ...
Both sensory and metabolic processes guide food intake. Olfactory inputs help coordinate food appreciation and selection, but their role in food consumption and post-feeding physiology remains poorly understood. In this study, using Drosophila melanogaster as a model system, we investigated the effects of olfactory sensory neurons (OSNs) on food consumption, metabolism, and stress responses. We found that dysfunction of OSNs affects diverse processes, including decreased food consumption, increased triacylglycerol level, enhanced stress resistance to starvation or desiccation, and decreased cold resistance. Decreased neuropeptide F receptor (NPFR) level or increased insulin activity in OSNs inhibited food consumption, while impaired NPF signaling or insulin signaling in OSNs increased resistance to starvation and desiccation. These studies provide insights into the function of the olfactory system in control of feeding behaviors and physiology.
... In day-to-day human life, the sense of smell has a role in eating behavior [72], social and emotional interactions [73], forming memories, and avoiding hazardous situations [74]. However, we still underestimate the relevance and importance of this sense on our quality of life and well-being [75]. ...
Olfactory perception guides daily decisions regarding food consumption, social interactions, and predator avoidance in all mammalian species. Volatile inputs, comprising odorants and pheromones, are relayed to the olfactory bulb (OB) from nasal sensory neurons cells and transferred to secondary processing regions within the brain. Olfaction has recently been shown to shape homeostatic and maladaptive processes of energy intake and expenditure through neuronal circuits involving the medial basal hypothalamus. Reciprocally, gastrointestinal hormones, such as ghrelin and leptin, the secretion of which depends on satiety and adiposity levels, might also influence olfactory sensitivity to alter food-seeking behaviors. Here, in addition to reviewing recent updates on identifying these neuronal networks, we also discuss how bidirectional neurocircuits existing between olfactory and energy processing centers can become dysregulated during obesity.
... For example, parotid salivary secretion (the main component of appetitive salivary anticipation) depends upon exposure to olfactory signals [90], and olfactomotor responses to odors vary according to perceptions of pleasantness [91]. Hedonic ratings of food smells are associatively learned and depend upon the food-and hunger-related context [92]. Evidence that individuals with eating disorders show a heightened sensitivity to smells [93,94] raises the possibility that interoceptive processing abnormalities triggered by olfactory stimulation play a reinforcing role. ...
Purpose of Review
Abnormal interoception has been consistently observed across eating disorders despite limited inclusion in diagnostic conceptualization. Using the alimentary tract as well as recent developments in interoceptive neuroscience and predictive processing as a guide, the current review summarizes evidence of gastrointestinal interoceptive dysfunction in eating disorders.
Recent Findings
Eating is a complex process that begins well before and ends well after food consumption. Abnormal prediction and prediction-error signals may occur at any stage, resulting in aberrant gastrointestinal interoception and dysregulated gut sensations in eating disorders. Several interoceptive technologies have recently become available that can be paired with computational modeling and clinical interventions to yield new insights into eating disorder pathophysiology.
Summary
Illuminating the neurobiology of gastrointestinal interoception in eating disorders requires a new generation of studies combining experimental probes of gut physiology with computational modeling. The application of such techniques within clinical trials frameworks may yield new tools and treatments with transdiagnostic relevance.
... As shown in Figure 4, additional predominant sensory stimuli may be needed to enrich the pre-travel experience information and help form the destination image. For example, culinary or food tourism requires additional olfactory stimuli for food-trial activities, with short exposure to food odor found to enhance appetite and hunger feelings (Yeomans, 2006). This can provide information on the food texture (Rolls, 2005). ...
Purpose
The use of extended reality (XR) to create memorable experiences has attracted considerable attention, especially in tourism. Multisensory XR offers a new way of virtually previewing a destination before physical holidays. This study aims to explore how multisensory XR can be used at each stage of the tourism experience journey. This study established a model for how destination-image formation is affected by multisensory XR in each phase of tourism experience.
Design/methodology/approach
The authors followed the preferred reporting items for systematic reviews and meta-analyses guidelines to review studies published between 2013 and 2020, gathered from four research databases. The authors identified the predominant XR technology and sensory stimuli based on the characteristics of various tourism domains. The authors synthesized the previous studies to explain destination-image formation by using multisensory XR.
Findings
This study summarized the XR study distribution among the three stages of the tourism experience journey. The authors identified the predominant sensory stimuli and dominant XR application and developed a destination-image formation model by using multisensory XR.
Originality/value
This study highlights the holistic approach of multisensory XR in the tourism experience journey in relation to various tourism domains. It also contributes to destination-image formation in the virtual environment by providing multisensory experiences of predominant sensory stimuli at each stage.
... Por lo que, identificar los olores relacionados con los alimentos y asociarlos con nuestras preferencias alimentarias conlleva de forma implícita una serie de procesos aprendizajes continuos. De esta forma se puede indicar que la elección de los alimentos implica una asociación entre el olor del alimento (indicadores químicos) y las vías sensoriales como la gustativa, visual o táctil que varían dependiendo de las experiencias individuales, lo cual delimita la señal olfativa asociada con el alimento que tiene valor hedónico (Yeomans, 2006;Poncelet et al., 2010). ...
El procesamiento neurobiológico de la conducta alimentaria se transmite a los núcleos corticales y subcorticales donde se integran estímulos multisensoriales, como los olfativos, asociados a la emoción, aprendizaje y memoria. Con esta revisión, se analizan y describen las implicaciones asociadas entre la memoria emocional y los estímulos olfativos, así como sus bases neurobiológicas. Además, se indican los principales procesos cognitivos implicados en la preferencia de alimentos hipo e hipercalóricos y su relación con los trastornos alimentarios como la obesidad, condición que converge con efecto negativo durante la enfermedad COVID-19. Se requiere de la aplicación de métodos neuropsicológicos que incluyan la medición de efecto de los estímulos multisensoriales para evaluar la preferencia alimentaria. Puesto que los estímulos olfativos y la memoria emocional participan en la elección de alimentos, lo que propician o no, el desarrollo de trastornos en la conducta alimentaria. El adaptar los paradigmas de la neuropsicología como el Stroop alimentario apuntalaría la generación de estrategias para la prevención del desarrollo de trastornos alimentarios como la obesidad.
... First, cephalic responses have been demonstrated to regulate feelings of hunger and satiety. Cues associated with the food, such as smell of food or the regular meals times and places, have been shown to increase appetite in humans and subsequently trigger salivation, ghrelin, gastric acid release and a cascade of hormonal changes (Johnson and Wildman, 1983;Yeomans, 2006). Animal research showed that in food deprived animals, cephalic responses to the smell of food trigger food search behavior (Lushchak et al., 2015). ...
Food anticipatory hormonal responses (cephalic responses) are proactive physiological processes, that allow animals to prepare for food ingestion by modulating their hormonal levels in response to food cues. This process is important for digesting food, metabolizing nutrients and maintaining glucose levels within homeostasis. In this systematic review, we summarize the evidence from animal and human research on cephalic responses. Thirty-six animal and fifty-three human studies were included. The majority (88%) of studies demonstrated that hormonal levels are changed in response to cues previously associated with food intake, such as feeding time, smell, and sight of food. Most evidence comes from studies on insulin, ghrelin, pancreatic polypeptide, glucagon, and c-peptide. Moreover, impaired cephalic responses were found in disorders related to metabolism and food intake such as diabetes, pancreatic insufficiency, obesity, and eating disorders, which opens discussions about the etiological mechanisms of these disorders as well as on potential therapeutic opportunities.
... In parallel, the metabolic state of the subject can regulate odor function depending on homeostatic requirements. Therefore, it emerges that olfaction influences appetite behaviors and that the olfactory system is also linked to the metabolic state of the individual [20,22,23]. ...
Palatable food can promote overfeeding beyond homeostatic requirements, thereby constituting a major risk to obesity. Here, the lack of cannabinoid type 1 receptor (CB1) in dorsal telencephalic glutamatergic neurons (Glu-CB1-KO) abrogated the overconsumption of palatable food and the development of obesity. On low-fat diet, no genotype differences were observed. However, under palatable food conditions, Glu-CB1-KO mice showed decreased body weight and food intake. Notably, Glu-CB1-KO mice were protected from alterations in the reward system after high-fat diet feeding. Interestingly, obese wild-type mice showed a superior olfactory detection as compared to mutant mice, suggesting a link between overconsumption of palatable food and olfactory function. Reconstitution of CB1 expression in olfactory cortex in high-fat diet-fed Glu-CB1-KO mice using viral gene delivery partially reversed the lean phenotype concomitantly with improved odor perception. These findings indicate that CB1 in cortical glutamatergic neurons regulates hedonic feeding, whereby a critical role of the olfactory cortex was uncovered as an underlying mechanism.
... These conflicting results may be explained by interindividual differences in taste preferences. This notion has gained support from a study where odor pleasantness indeed increased more after exposure with sucrose than after exposure without taste, but only for participants that liked sweet taste to begin with (Yeomans, 2006). ...
Repeated exposure can change the perceptual and hedonic experience of food flavors. Associative learning during which a flavor's odor component is affected by co-exposure with taste is thought to play a central role in this process. However, changes can also arise due to mere-exposure to the odor in itself. The aim of this study was to dissociate effects of associative learning from effects of mere-exposure by repeatedly presenting one odor together with a sweet taste and another without. Sixty individuals participated in two testing sessions separated by an exposure phase during which the stimuli were presented as flavorants in chewing gums. The gums were chewed three times per day for five days. Ratings of odor sweetness, odor pleasantness, odor intensity enhancement by taste, and odor referral to the mouth were collected at both sessions. Consistent with the idea of mere-exposure, odor pleasantness increased between the sessions independently of whether the odor had been exposed with or without sucrose. However, contrary to expectation, we found no evidence for associative learning effects on any of the outcomes. In addition, exploratory equivalence tests demonstrated that these effects were either absent or insignificant in magnitude. Taken together, our results suggest that associative learning effects on odor-taste interaction are either smaller than previously thought or highly dependent on the experimental setting. Future studies are needed to dissociate these two possibilities and, if experimental settings can be identified that reliably produce such effects, to pinpoint boundary conditions that prevents associative learning from taking place.
... Olfactory perception has an important role in appetite and can modify the sense of taste and the enjoyment of food [2]. Whether olfactory impairment (OI) is co-causative for obesity or an effect of expanded fat mass and linked metabolic abnormalities in humans is debated. ...
Purpose
This study evaluates among middle-aged subjects with obesity the prevalence of olfactory impairment (OI) with respect to normative values and its correlation with body composition, cognition, sleep quality, and inflammation.
Methods
In 60 (31 women, 29 men) volunteers with a body mass index ≥ 30 to ≤ 40 kg/m², aged ≥ 50 to ≤ 70 years, we assessed olfaction by the Sniffin’ Stick test. We measured anthropometrics, body composition and metabolic profiles and evaluated cognition by the MiniMental State Examination (MMSE) and sleep disturbances by the Insomnia Severity Index (ISI). Patients were classified into two groups according to a total olfactory score (odor Threshold, Discrimination, Identification, TDI) below or above the 25th percentile from age and gender-adjusted normative data.
Results
Overall, 25 subjects (42%) had OI (TDI < 25th percentile). The largest differences between subjects with and without OI were observed in discrimination and identification scores, with a large overlap in olfactory threshold. Subjects with an abnormal TDI showed significantly higher fat mass index, ISI scores and urinary neopterin and lower MMSE scores than those without OI. By multivariable logistic regression, MMSE, ISI score and urinary neopterin were significantly associated to OI.
Conclusions
Among middle-aged subjects with stage I and II obesity, OI is highly prevalent and is independently associated with poor self-reported sleep quality, lower cognition scores and higher levels of the inflammatory marker neopterin.
... Proper diet is important to the health; hence aroma and taste are essential for proper diet because these are the key determining factor in acceptance and palatability of food. The aroma in the food determines the taste and has many functions such as appetite enhancement, salivation (Rogers and Hill 1989;Engelen et al. 2003;Yeomans 2006), and pleasantness during eating, stimulation, and release of insulin (Johnson and Wildman 1983) and gastric acid (Feldman and Richardson 1986). Besides these, it protects from foul and hazardous food. ...
Biofortification is the process of enhancing the content and density of vitamins and minerals that are improving nutritional quality in a staple crop through conventional plant breeding or agronomic practices or using transgenic approaches. Rice (Oryza sativa L.) ranks second in most widely consumed cereals in the world and used as a staple food for more than 60% of the world population. Micronutrients are essential for plant growth and development as well as for animal and human health. In the last two decades, the concept of hidden hunger arises in which one-sixth of the world’s population suffers from hunger that is a deficiency of micronutrients, vitamins, and nutrients. Rice grain has large genetic variability in the concentration of micronutrients; hence, it is included in the biofortification program, and breeding of new rice cultivars with an enhanced level of grain micronutrients is one of the most sustainable and cost-effective strategies for preventing hidden hunger. To overcome the major problem of hidden hunger and looking to the future, the agricultural community has a fundamental responsibility to produce crop enriched with minerals and vitamins to secure national health, and there is a need to increase the nutritional quality of food through various methods like supplementation, fortifications, etc. Aroma acts as a supporting trait for nutrition; therefore, it needs to be considered in biofortification. It has been shown to enhance food appetite in hungry and in satiated states, so it may be used to stimulate meal initiation and appetite in people that are malnourished. Here the process and progress of biofortification with micronutrients have been briefly described, and future prospects to alleviate widespread micronutrient deficiencies in the human population are discussed.
... Si bien se sabe que el olfato juega un papel fundamental en el consumo de alimentos (Yeomans, 2006), no está claro si las habilidades olfatorias están ligadas a la adiposidad a través de influencias directas sobre la conducta alimentaria. En la última década un número creciente de estudios ha intentado dar respuesta a esta cuestión investigando las habilidades olfatorias en grupos de distinto peso corporal (Islam et al., 2015;Peng et al., 2019). ...
Aun cuando el sentido del olfato es fundamental para la percepción de los alimentos, su relación con la obesidad ha sido poco investigada. Este artículo es una revisión de la literatura sobre esa relación. La evidencia actual tanto en animales como en humanos apoya la hipótesis de que el olfato está alterado en esta condición. Estudios recientes señalan que los individuos obesos podrían tener una mayor sensibilidad a los olores de alimentos altos en calorías, y menor para los de bajo valor calórico incluidos los no asociados con alimentos. El estudio de la percepción quimiosensorial es un área prometedora para avanzar en el entendimiento de los mecanismos involucrados en la obesidad.
... More recently, continuous theta bursts of transcranial magnetic stimulation to the right orbitofrontal cortex produced impaired odor perception [38]. Olfaction is known to be a primary cue for the appearance and control of appetite and substance abuse, as odors stimulate the same brain areas as those activated by addictive substances [39]. Still, the neurophysiology underlying the link between odor and impulsivity is not clear, and to our knowledge, no work exists imaging impulsive children medicated with LDX while stimulated by odor cues. ...
Introduction
Lisdexamfetamine (LDX) is a drug used to treat ADHD/impulsive patients. Impulsivity is known to affect inhibitory, emotional and cognitive function. On the other hand, smell and odor processing are known to be affected by neurological disorders, as they are modulators of addictive and impulsive behaviors specifically. We hypothesize that, after LDX ingestion, inhibitory pathways of the brain would change, and complementary behavioral regulation mechanisms would appear to regulate decision-making and impulsivity.
Methods
20 children were studied in an aleatory crossover study. Imaging of BOLD-fMRI activity, elicited by olfactory stimulation in impulsive children, was performed after either LDX or placebo ingestion.
Results
Findings showed that all subjects that underwent odor stimulation presented activations of similar intensities in the olfactory centers of the brain. This contrasted with inhibitory regions of the brain such as the cingulate cortex and frontal lobe regions, which demonstrated changed activity patterns and intensities. While some differences between the placebo and medicated states were found in motor areas, precuneus, cuneus, calcarine, supramarginal, cerebellum and posterior cingulate cortex, the main changes were found in frontal, temporal and parietal cortices. When comparing olfactory cues separately, pleasant food smells like chocolate seemed not to present large differences between the medicated and placebo scenarios, when compared to non-food-related smells.
Conclusions
We demonstrated that LDX, first, altered the inhibitory pathways of the brain, second, increased activity in large amounts of brain regions which were not activated by smell in drug-naïve patients, third, facilitated a complementary behavioral regulation mechanism, run by the cerebellum, which regulated decision-making and impulsivity in motor and frontal structures.
... Food intake is a complex process in which both homoeostatic regulation and hedonic sensations are critically involved. Most sensory systems influence food detection and consumption [1][2][3][4]. However, of all the sensory modalities, olfaction contributes the most to the hedonic evaluation of a food and its eventual possible consumption [1,2,5]. ...
Olfaction and satiety status influence each other: cues from the olfactory system modulate eating behavior, and satiety affects olfactory abilities. However, the neural mechanisms governing the interactions between olfaction and satiety are unknown. Here, we investigate how an animal’s nutritional state modulates neural activity and odor representation in the mitral/tufted cells of the olfactory bulb, a key olfactory center that plays important roles in odor processing and representation. At the single-cell level, we found that the spontaneous firing rate of mitral/tufted cells and the number of cells showing an excitatory response both increased when mice were in a fasted state. However, the neural discrimination of odors slightly decreased. Although ongoing baseline and odor-evoked beta oscillations in the local field potential in the olfactory bulb were unchanged with fasting, the amplitude of odor-evoked gamma oscillations significantly decreased in a fasted state. These neural changes in the olfactory bulb were independent of the sniffing pattern, since both sniffing frequency and mean inhalation duration did not change with fasting. These results provide new information toward understanding the neural circuit mechanisms by which olfaction is modulated by nutritional status.
... This learning will result in higher desire/consumption or in avoidance when such sensory signals are presented [1,2]. Different studies show the influence that the exposure to sensory cues has in wanting for food [3,4]. ...
It is widely recognized that smelling food results in a mouth-watering feeling and influences appetite. However, besides changes in volume, little is known about the effects that food odours have on the composition of saliva. The aim of the present study was to access the effects that smelling bread has on saliva proteome and to compare such effects with those of chewing and ingesting it. Besides a significant increase in saliva flow rate, together with a decrease in total protein concentration, bread odour induced changes in the proportion of different salivary proteins. The expression levels of two spots of cystatins and two spots of amylase increased due to olfactory stimulation, similar to what happened with bread mastication, suggesting that odour can allow anticipation of the type of food eaten and consequently the physiological oral changes necessary to that ingestion. An interesting finding was that bread odour increased the expression levels of several protein spots of immunoglobulin chains, which were decreased by both bread or rice mastication. This may be of clinical relevance since food olfactory stimulation of salivary immunoglobulins can be used to potentiate the oral immune function of saliva. Moreover, the effects of bread odour in the levels of salivary proteins, previously observed to be involved in oral food processing led to the hypothesis of an influence of this odour in the sensory perception of foods further ingested. Further studies are needed to elucidate this point, as well as whether the changes observed for bread odour are specific, or if different food odours lead to similar salivary proteome responses.
... Desde hace un par de décadas se sabe que el olfato se relaciona con la conducta de ingesta de alimentos y desempeña un papel importante en la decisión de lo que se va a consumir (es decir, participa en la evaluación hedónica de los alimentos); asimismo, influye en el apetito y la saciedad del humano [29]. ...
Nowadays, it is well accepted that obesity and metabolic syndrome are diseases that constitute a global public health issue. In consequence, the interest in the study of the effects these pathologies produce in the central nervous system has greatly increased in the last decades. One of the most overlooked topics in the literature is the impact they exert in sensory systems, among which is olfaction. The olfactory system is related to a number of vital functions, like the activation of defense mechanisms, contribution to appetitive and digestive reflexes, recognition of conspecifics, and even has socio-sexual implications. It has been discovered that the olfactory system also plays a crucial role in food intake, the choice of foods, appetite and satiety mechanisms; therefore, it is involved in obesity development. Clinical studies have proven that obese patients exhibit hyposmia more frequently than aged-matched healthy controls. Olfactory alterations have also been found in obese rodents or in animals with similar features of human metabolic syndrome. The causes of this association are still being investigated. This work reviews the studies that have tried to understand this association from a preclinical and clinical approach as well as those biological mechanisms that could be involved. The evidences here presented suggest that obesity and metabolic syndrome affect the adequate function of olfactory sensory system.
Olfactory dysfunction and cognition decline are frequently observed in Alzheimer's disease (AD); however, very little is known about whether olfactory disorders trigger cognitive impairment. Here, we induced olfactory loss in mice and investigated whether and how olfactory loss induces cognitive impairment and anxiety behavior. Olfactory loss not only causes a significant decrease in food intake and body weight and an increase in O 2 consumption but also induces cognitive impairment and anxiety behavior. Alteration of the gut microbiota induced by olfactory loss is followed by changes in cecal short fatty acids and serum neurotransmitters. Hippocampus proteome and fecal microbial transplantation provides further support for the mechanisms by which olfactory loss triggers cognitive impairment and anxiety behavior via the microbiota–gut-brain axis. Our study is expected to provide some of the first evidence for olfactory dysfunction in triggering cognitive impairment through the microbiota-gut-brain axis.
Approximately 30–60% of people suffer from olfactory dysfunction (OD) such as hyposmia or anosmia after being diagnosed with COVID-19; 15–20% of these cases last beyond resolution of the acute phase. Previous studies have shown that olfactory training can be beneficial for patients affected by OD caused by viral infections of the upper respiratory tract. The aim of the study is to evaluate whether a multisensory olfactory training involving simultaneously tasting and seeing congruent stimuli is more effective than the classical olfactory training. We recruited 68 participants with persistent OD for two months or more after COVID-19 infection; they were divided into three groups. One group received olfactory training which involved smelling four odorants (strawberry, cheese, coffee, lemon; classical olfactory training). The other group received the same olfactory stimuli but presented retronasally (i.e., as droplets on their tongue); while simultaneous and congruent gustatory (i.e., sweet, salty, bitter, sour) and visual (corresponding images) stimuli were presented (multisensory olfactory training). The third group received odorless propylene glycol in four bottles (control group). Training was carried out twice daily for 12 weeks. We assessed olfactory function and olfactory specific quality of life before and after the intervention. Both intervention groups showed a similar significant improvement of olfactory function, although there was no difference in the assessment of quality of life. Both multisensory and classical training can be beneficial for OD following a viral infection; however, only the classical olfactory training paradigm leads to an improvement that was significantly stronger than the control group.
Stress-related overeating can lead to excessive weight gain, increasing the risk of metabolic and cardiovascular disease. Mindfulness meditation has been demonstrated to reduce stress and increase interoceptive awareness and could, therefore, be an effective intervention for stress-related overeating behavior. To investigate the effects of mindfulness meditation on stress-eating behavior, meditation-naïve individuals with a tendency to stress-eat (N = 66) participated in either a 31-day, web-based mindfulness meditation training or a health training condition. Behavioral and resting-state fMRI data were acquired before and after the intervention. Mindfulness meditation training, in comparison to health training, was found to significantly increase mindfulness while simultaneously reducing stress- and emotional-eating tendencies as well as food cravings. These behavioral results were accompanied by functional connectivity changes between the hypothalamus, reward regions, and several areas of the default mode network in addition to changes observed between the insula and somatosensory areas. Additional changes between seed regions (i.e., hypothalamus and insula) and brain areas attributed to emotion regulation, awareness, attention, and sensory integration were observed. Notably, these changes in functional connectivity correlated with behavioral changes, thereby providing insight into the underlying neural mechanisms of the effects of mindfulness on stress-eating.
Clinical trial on the ISRCTN registry: trial ID ISRCTN12901054
Olfaction is the most ancient sense and is needed for food‐seeking, danger protection, mating and survival. It is often the first sensory modality to perceive changes in the external environment, before sight, taste or sound. Odour molecules activate olfactory sensory neurons that reside on the olfactory epithelium in the nasal cavity, which transmits this odour‐specific information to the olfactory bulb (OB), where it is relayed to higher brain regions involved in olfactory perception and behaviour. Besides odour processing, recent studies suggest that the OB extends its function into the regulation of food intake and energy balance. Furthermore, numerous hormone receptors associated with appetite and metabolism are expressed within the OB, suggesting a neuroendocrine role outside the hypothalamus. Olfactory cues are important to promote food preparatory behaviours and consumption, such as enhancing appetite and salivation. In addition, altered metabolism or energy state (fasting, satiety and overnutrition) can change olfactory processing and perception. Similarly, various animal models and human pathologies indicate a strong link between olfactory impairment and metabolic dysfunction. Therefore, understanding the nature of this reciprocal relationship is critical to understand how olfactory or metabolic disorders arise. This present review elaborates on the connection between olfaction, feeding behaviour and metabolism and will shed light on the neuroendocrine role of the OB as an interface between the external and internal environments. Elucidating the specific mechanisms by which olfactory signals are integrated and translated into metabolic responses holds promise for the development of targeted therapeutic strategies and interventions aimed at modulating appetite and promoting metabolic health.
Odors guide food seeking, and food intake modulates olfactory function. This interaction is mediated by appetite-regulating hormones like ghrelin, insulin, and leptin, which alter activity in the rodent olfactory bulb, but their effects on downstream olfactory cortices have not yet been established in humans. The olfactory tract connects the olfactory bulb to the cortex through 3 main striae, terminating in the piriform cortex (PirC), amygdala (AMY), olfactory tubercule (OT), and anterior olfactory nucleus (AON). Here, we test the hypothesis that appetite-regulating hormones modulate olfactory processing in the endpoints of the olfactory tract and the hypothalamus. We collected odor-evoked functional magnetic resonance imaging (fMRI) responses and plasma levels of ghrelin, insulin, and leptin from human subjects (n = 25) after a standardized meal. We found that a hormonal composite measure, capturing variance relating positively to insulin and negatively to ghrelin, correlated inversely with odor intensity ratings and fMRI responses to odorized vs. clean air in the hypothalamus, OT, and AON. No significant correlations were found with activity in PirC or AMY, the endpoints of the lateral stria. Exploratory whole-brain analyses revealed significant correlations near the diagonal band of Broca and parahippocampal gyrus. These results demonstrate that high (low) blood plasma concentrations of insulin (ghrelin) decrease perceived odor intensity and odor-evoked activity in the cortical targets of the medial and intermediate striae of the olfactory tract, as well as the hypothalamus. These findings expand our understanding of the cortical mechanisms by which metabolic hormones in humans modulate olfactory processing after a meal.
Olfactory stimulation promotes motor activity in adults. However, the effect of odor stimulation on children's motor activity is not well understood. In this study, given the importance of feeding behavior in children, and the involvement of balance ability in that behavior, we examined the effects of soy sauce and vanilla odors, as food‐related olfactory stimuli, on balance ability in 67 healthy, normal developing children aged 3–6 years. The participants were randomly divided into water (control), soy sauce, and vanilla groups, and their balance ability was assessed before and after olfactory stimulation using the Functional Reach Test (FRT). The results showed that the soy sauce and vanilla odor exposure extended the reaching distance and forward shift in the center of gravity in the FRT, indicating that food odors improved the balance ability of children.
Practical Applications
We have shown that soy sauce and vanilla odors improve balance ability in children. Such odor stimulation could be useful for children with cerebral palsy who have balance disorders. A better understanding of the neural mechanisms that link olfactory stimulation with motor activity will facilitate the therapeutic application of odors for children with motor disorders.
Olfactory cues play a key role in natural behaviors such as finding food, finding mates, and avoiding predators. In principle, the ability of the olfactory system to carry out these perceptual functions would be facilitated by signaling related to an organism's physiological state. One candidate pathway includes a direct projection from the hypothalamus to the main olfactory bulb, the first stage of olfactory sensory processing. The pathway from the hypothalamus to the main olfactory bulb is thought to include neurons that express the neuropeptide orexin, although the proportion that is orexinergic remains unknown. A current model proposes that the orexin population is heterogeneous, yet it remains unknown whether the proportion that innervates the main olfactory bulb reflects a distinct subpopulation of the orexin population. Herein, we carried out combined retrograde tract tracing with immunohistochemistry for orexin-A in the mouse to define the proportion of hypothalamic input to the main olfactory bulb that is orexinergic and to determine what fraction of the orexin-A population innervates the bulb. The numbers and spatial positions of all retrogradely labeled neurons and all the orexin-A-expressing neurons were quantified in sequential sections through the hypothalamus. Retrogradely labeled neurons were found in the ipsilateral hypothalamus, of which 22% expressed orexin-A. The retrogradely labeled neurons that did and did not express orexin-A could be anatomically distinguished based on their spatial position and cell body area. Remarkably, only 7% of all the orexin-A neurons were retrogradely labeled, suggesting that only a small fraction of the orexin-A population directly innervate the main olfactory bulb. These neurons spatially overlapped with the orexin-A neurons that did not innervate the bulb, although the two cell populations were differentiated based on cell body area. Overall, these results support a model in which olfactory sensory processing is influenced by orexinergic feedback at the first synapse in the olfactory processing pathway.
Objective:
Significant advances have been made in our understanding of the neural substrates of human chemosensory processing, involving the piriform cortex, insula and orbitofrontal cortex (OFC). However, the important and challenging issues are to localize the brain regions with high anatomic precision that can causally produce chemosensory perception and further delineate the topography of different classifications of chemosensory perception.
Methods:
We quantitatively measured subjective responses of chemosensory perception to intracranial electrical stimulation over the brain in neurosurgical patients (n = 302) with medically refractory epilepsy.
Results:
The chemosensory perceptions including olfaction, gustation and chemesthesis were elicited in 21 of 302 patients (7%). Chemosensory responses were evoked in 53 (0.2%) of 21,661 stimulated sites. The highest response rate (1.8%) was in the insula (37/2,051 stimulated sites from 15/163 patients). The chemosensory perception emerged predominantly during stimulations of the insula along the central sulcus axis. Notably, there existed a distinct pattern that the anteroventral insula predominately represented orthonasal olfaction, while different chemosensory modalities converged in the mid-dorsal insula.
Interpretation:
This study provided a detailed characterization of chemosensory perception across the brain, especially in the insula. These results suggest that the cortex along the banks of the central sulcus of the insula may play a role in producing the supramodal sensation of flavor. It also indicates that dysfunction of the central insula should be considered during the evaluation of chemosensory-related epileptic seizures. This article is protected by copyright. All rights reserved.
Olfaction and food intake are interrelated and regulated. In the process of feeding, the metabolic signals in the body and the feeding signals produced by food stimulation are first sensed by the arcuate nucleus of hypothalamus and the nucleus tractus solitarius of brain stem, and then these neurons project to the paraventricular nucleus of hypothalamus. The paraventricular nucleus transmits the signals to other brain regions related to feeding and regulates feeding behavior. In this process, olfactory signals can be transmitted to hypothalamus through olfactory bulb and olfactory cortex to regulate feeding behavior. At the same time, gastrointestinal hormones (ghrelin, insulin, leptin, etc.) and some neurotransmitters (acetylcholine, norepinephrine, serotonin, endocannabinoid, etc.) produced in the process of feeding act on the olfactory system to regulate olfactory function, which in turn affects the feeding itself. This review summaries the research progress of the interaction between olfaction and food intake and its internal mechanism from the aspects of neuronal and hormonal regulation.
Previous research has shown the influence of smell on emotions, memories, and body image. However, most of this work has taken place in laboratory settings and little is known about the influence of smell in real-world environments. In this paper, we present novel insights gained from a field study investigating the emotional effect of smell on memories and body image. Taking inspiration from the cultural design probes approach, we designed QuintEssence, a probe package that includes three scents and materials to complete three tasks over a period of four weeks. Here, we describe the design of QuintEssence and the main findings based on the outcomes of the three tasks and a final individual interview. The findings show similar results between participants based on the scent. For example, with cinnamon, participants experienced feelings of warmth, coziness, happiness, and relaxation; they recalled blurred memories of past moments about themselves and reported a general feeling of being calm and peaceful towards their bodies. Our findings open up new design spaces for multisensory experiences and inspire future qualitative explorations beyond laboratory boundaries.
Anticipatory physiological responses to food were first reported by Ivan Pavlov a century ago but the associated neural mechanism is still ill-defined. Here, we identified two types of neurons in the basolateral amygdala (BLA), which are activated by sweetener (saccharin) or water after sucrose conditioning, representing expected sweet taste and unmet expectation, respectively. Saccharin-induced met-expectation of sweet taste enhances, while H 2 O-induced unmet-expectation deteriorates, glucose metabolism in peripheral tissues. Deletion of saccharin-responsive neurons in BLA impaired saccharin-induced increase in insulin sensitivity. Deletion of H 2 O-responsive neurons in BLA improved glucose intolerance by unmet-expectation. Saccharin- and H 2 O-responsive neurons had different gene expressions. Our data suggest that the gap between the expected incoming sugar and sweet taste is evaluated by distinct BLA neurons to control peripheral glucose metabolism.
One-Sentence Summary
Neurons in the basolateral amygdala control blood glucose levels by comparing anticipated sugar intake and sweet taste
Auch wenn der visuelle Sinn die am meisten untersuchte Sinnesmodalität darstellt, müssen wir Wahrnehmung als einen Prozess verstehen, bei dem nicht nur unterschiedliche Sinne in unterschiedlichem Maße beteiligt sind, sondern bei dem sich unsere Sinne gegenseitig ergänzen. Vor allem dem Hörsinn kommt dabei große Bedeutung zu. Hören und Sehen gehen nämlich Hand in Hand. Gleiches gilt für Riechen und Schmecken. Betrachten wir im Folgenden zunächst grundlegende und sinnesspezifische Wahrnehmungsprozesse, bevor wir uns zum Ende des Kapitels mit der Frage des Zusammenspiels der verschiedenen Sinneskanäle beschäftigen werden.
The sensory eating experience is a significant determinant of control of food consumption, frequently ascribed to the favorable hedonic reaction affiliated with some sensory signals. But palatability is just one component of the sensory experience. Before, during, and after eating, sensory signals based on the vision, aroma, texture, and palate of food are functional. These perceptual signals also influence the guidance of energy intake beyond their role in preferences. The focus of this chapter is to look at sensory food behavior drivers and highlight latest developments in our knowledge of how to use certain sensory features to encourage better control of food intake. We recognize the function of pictorial and odor signs in recognizing nourishment in the surroundings, regulating food selection and eating cognition, and highlighting how textures and flavors affect diet quantity and satiety growth postconsumption.
Obesity has reached epidemic proportions in the United States and other developed nations. In the United States, 27% of adults are obese and an additional 34% are overweight. Research in the past decade has shown that genetic influences clearly predispose some individuals to obesity. The marked increase in prevalence, however, appears to be attributable to a toxic environment that implicitly discourages physical activity while explicitly encouraging the consumption of supersized portions of high-fat, high-sugar foods. Management of the obesity epidemic will require a two-pronged approach. First, better treatments, including behavioral, pharmacologic, and surgical interventions, are needed for individuals who are already obese. The second and potentially more promising approach is to prevent the development of obesity by tackling the toxic environment. This will require bold public policy initiatives such as regulating food advertising directed at children. The authors call not for the adoption of a specific policy initiative, but instead propose that policy research, based on viewing obesity as a public health problem, become a central focus of research.
Evaluative conditioning refers to changes in the liking of a stimulus that are due to the fact that the stimulus has been paired with other, positive or negative stimuli. Although evaluative conditioning appears to be subjected to certain boundary conditions, significant evaluative conditioning effects have been obtained using a large variety of stimuli and procedures. Some data suggest that evaluative conditioning can occur under conditions that do not support other forms of Pavlovian conditioning, and several models have been proposed to account for these differences. In the present article, the authors summarize the available literature, draw conclusions where possible, and provide suggestions for future research.
Certain odors are routinely described as smelling sweet, This phenomenon may result from the co-occurrence of such odors and tastes outside the laboratory. Experiment 1 tested this possibility by pairing a selected odor with sucrose and another with citric acid in a masked design, using 24-h spaced sessions, preceded and followed by ratings of the odors' taste attributes when sniffed and when rated with tastes in solution. Following conditioning, the odor paired with sucrose smelled sweeter and with citric acid, sourer. In Experiment 2, contingency awareness was examined using a recognition measure, in an otherwise similar design. Again, odors smelled sweeter and sourer postconditioning. Contingency aware and unaware subjects did not differ in performance. Experiment 3 examined an exposure account of these changes, using a similar paradigm to Experiment 1, but with no exposures to sucrose or citric acid. No changes in odor taste attributes were observed. Overall, these findings demonstrate that associative learning, irrespective of awareness, has an important role in tile acquisition of odor-taste qualities.
A given stimulus can induce a pleasant or unpleasant sensation depending on the subject's internal state. The word alliesthesia is proposed to describe this phenomenon. It is, in itself, an adequate motivation for behavior such as food intake or thermoregulation. Therefore, negative regulatory feedback systems, based upon oropharingeal or cutaneous thermal signals are peripheral only in appearance, since the motivational component of the sensation is of internal origin. The internal signals seem to be complex and related to the set points of some regulated variables of the "milieu interieur," like set internal temperature in the case of thermal sensation (15). Alliesthesia can therefore explain the adaptation of these behaviors to their goals. Only three sensations have been studied— thermal, gustatory, and olfactory, but it is probable that alliesthesia also exists in such simple ways as in bringing a signal, usually ignored, to the subject's attention. For example, gastric contractions, not normally perceived, are felt in the state of hunger (16). Since alliesthesia relies on an internal input, it is possible that alliesthesia exists only with sensations related to some constants of the "milieu interieur" and therefore would not exist in visual or auditory sensations. As a matter of fact, luminous or auditory stimuli can be pleasing or displeasing in themselves, but there seems to be little variation of pleasure in these sensations, that is, no alliesthesia. There may be some esthetic value linked to these stimuli but it is a striking coincidence that they are in themselves rather neutral and that it is difficult to imagine a constant of the "milieu interieur" which could be possibly modified by a visual or an auditive stimulus—such as light of a certain wavelength or sound of a given frequency.
Exposure to food produces an increase in insulin secretion that is more pronounced in obese than in normal persons. We sought to replicate this finding as well as to determine whether insulin secretion could be influenced by thoughts about food and eating. Normal and obese subjects were presented in counterbalanced order with an external food stimulus or instructions to think about food and eating. Levels of insulin, salivary output, and hunger ratings were obtained prior to and immediately following stimulus presentation. All subjects displayed higher insulin levels following stimulus presentation, with the values for the obese higher than for normals. Although the insulin secretion of the obese was greater in response to the covert as opposed to the external stimulus, the difference was not significant. Salivary output following stimulus presentation was higher for the obese than normals, with hunger ratings increasing in both groups. These data support an expanded role of insulin as an appetite-inducing mechanism.
Obesity is a multifactorial and complex affectation that is characterized by a long-term excess energy intake (EI) above energy expenditure (EE). Since fat oxidation seems to be dependent on SNS activation and also seems to remain acutely unaffected by fat intake, this macronutrient is certainly partly responsible for this situation. In addition, high-fat intake does not induce as potent satiety signals or a compensation effect on subsequent EI as do diets rich in carbohydrates or proteins. Moreover, since alcohol intake acutely inhibits fat oxidation and does not promote subsequent compensation for its energy content, it should consequently be regarded as a substrate which can induce a positive energy balance under free-living conditions. Thus, in a weight reducing context, each energy substrate should be manipulated while taking into account its specific characteristics. Obesity has also often been associated to a decreased sympathetic nervous system (SNS) activity, hence sympathomimetic agents have been proposed as a possible way to partially correct this situation. Two of these agents are the widely consumed caffeine (CAF) and the pungent principle of hot red pepper, capsaicin (CAP), which acutely increase EE and reduce EI under some circumstances. Furthermore, other factors like dietary fibers, that have been shown to increase satiety and fullness, and reduce EI in some cases, should also be considered.
A tasteless odor will smell sweeter after being sampled by mouth with sucrose and will smell sourer after being sampled with citric acid. This tasty-smell effect was found in experiments that compared odor-taste and color-taste pairings. Using odors and colors with minimal taste (Experiment 1), the authors found that repeated experience of odor-taste mixtures produced conditioned changes in odor qualities that were unaffected by intermixed color-taste trials (Experiment 2). An extinction procedure, consisting of postconditioning presentations of the odor in water, had no detectable effect on the changed perception of an odor (Experiments 3 and 4). In contrast, this procedure altered judgments about the expected taste of colored solutions. Evaluative conditioning (conditioned changes in liking) is claimed to be resistant to extinction. However, these results suggest that resistance to extinction in odors is related to the way they are encoded rather than to their hedonic properties.
To test whether the palatability of a test meal altered compensatory eating following disguised high-energy fat and carbohydrate preloads.
Effects of preload energy (low, 265 kJ, or high, 1510 kJ) and test-meal palatability (bland or palatable) were contrasted within-subjects, with a between-subjects contrast of fat and carbohydrate preloads.
Twenty-four healthy, normal men (age 23.6+/-1.0 y, (body mass index) BMI 21.3+/-0.5).
Microstructural analysis of test meal intake and rated appetite in the four test conditions, plus diary-based weighed intake analysis of energy intake post-lunch.
Subjects ate significantly less at lunch after disguised high-energy fat or carbohydrate preloads relative to the low-energy preload, and ate significantly more of the palatable than bland lunch in all conditions. The reduction in eating following the high-energy preload was significantly less in the palatable condition. Intake post-lunch did not differ between conditions, and overall subjects had higher daily energy intake on the days they consumed the high-energy preloads. Rated hunger was significantly less 30 min after the high- than low-energy preloads, but increased on tasting the palatable food in all conditions. The high-energy preloads suppressed appetite immediately post-lunch. No differences between fat and carbohydrate were found on any measure.
Manipulation of the palatability of a test meal modified the ability to respond to disguised high-energy preloads, with over-consumption most evident when disguised high-energy preloads were followed by a palatable food. Subsequent voluntary intake compensated for over-consumption of the palatable lunch, but not the high-energy preload.
Evaluative conditioning refers to changes in the liking of a stimulus that are due to the fact that the stimulus has been paired with other, positive or negative stimuli. Although evaluative conditioning appears to be subjected to certain boundary conditions, significant evaluative conditioning effects have been obtained using a large variety of stimuli and procedures. Some data suggest that evaluative conditioning can occur under conditions that do not support other forms of Pavlovian conditioning, and several models have been proposed to account for these differences. In the present article, the authors summarize the available literature, draw conclusions where possible, and provide suggestions for future research.
Obesity has reached epidemic proportions in the United States and other developed nations. In the United States, 27% of adults are obese and an additional 34% are overweight. Research in the past decade has shown that genetic influences clearly predispose some individuals to obesity. The marked increase in prevalence, however, appears to be attributable to a toxic environment that implicitly discourages physical activity while explicitly encouraging the consumption of supersized portions of high-fat, high-sugar foods. Management of the obesity epidemic will require a two-pronged approach. First, better treatments, including behavioral, pharmacologic, and surgical interventions, are needed for individuals who are already obese. The second and potentially more promising approach is to prevent the development of obesity by tackling the toxic environment. This will require bold public policy initiatives such as regulating food advertising directed at children. The authors call not for the adoption of a specific policy initiative, but instead propose that policy research, based on viewing obesity as a public health problem, become a central focus of research.
The traditional view of palatability was that it reflected some underlying nutritional deficit and was part of a homeostatically driven motivational system. However, this idea does not fit with the common observation that palatability can lead to short-term overconsumption. Here, we attempt to re-evaluate the basis of palatability, first by reviewing the role of salt-need both in the expression of liking for salty tastes, and paradoxically, in dissociating need from palatability, and second by examining the role of palatability in short-term control of appetite. Despite the clarity of this system in animals, however, most salt (NaCl) intake in man occurs in a need-free state. Similar conclusions can be drawn in relation to the palatability of food in general. Importantly, the neural systems underlying the hedonic system relating to palatability and homeostatic controls of eating are separate, involving distinct brain structures and neurochemicals. If palatability was a component of homeostatic control, reducing need-state should reduce palatability. However, this is not so, and if anything palatability exerts a stronger stimulatory effect on eating when sated, and over-consumption induced by palatability may contribute to obesity. Differential responsivity to palatability may be a component of the obese phenotype, perhaps through sensitisation of the neural structures related to hedonic aspects of eating. Together, these disparate data clearly indicate that palatability is not a simple reflection of need state, but acts to promote intake through a distinct hedonic system, which has inputs from a variety of other systems, including those regulating need. This conclusion leads to the possibility of novel therapies for obesity based on modulation of hedonic rather than homeostatic controls. Potential developments are discussed.
Perceptions of the flavors of foods or beverages reflect information derived from multiple sensory afferents, including gustatory, olfactory, and somatosensory fibers. Although flavor perception therefore arises from the central integration of multiple sensory inputs, it is possible to distinguish the different modalities contributing to flavor, especially when attention is drawn to particular sensory characteristics. Nevertheless, our experiences of the flavor of a food or beverage are also simultaneously of an overall unitary perception. Research aimed at understanding the mechanisms behind this integrated flavor perception is, for the most part, relatively recent. However, psychophysical, neuroimaging and neurophysiological studies on cross-modal sensory interactions involved in flavor perception have started to provide an understanding of the integrated activity of sensory systems that generate such unitary perceptions, and hence the mechanisms by which these signals are "functionally united when anatomically separated". Here we review this recent research on odor/taste integration, and propose a model of flavor processing that depends on prior experience with the particular combination of sensory inputs, temporal and spatial concurrence, and attentional allocation. We propose that flavor perception depends upon neural processes occurring in chemosensory regions of the brain, including the anterior insula, frontal operculum, orbitofrontal cortex and anterior cingulate cortex, as well as upon the interaction of this chemosensory "flavor network" with other heteromodal regions including the posterior parietal cortex and possibly the ventral lateral prefrontal cortex.
Animals readily acquire positive odor-taste hedonic associations, but evidence for this in humans remains weak and was explored further. Retronasal pairing of odors with sucrose or salty stimuli (Experiment 1) increased the rated sweetness of sucrose-paired odors without altering liking, although changes in odor pleasantness correlated with sucrose liking. Experience of odors with sucrose or quinine by sweet likers (Experiment 2) found increased pleasantness and sweetness for sucrose-paired odors, whereas quinine-paired odors became less liked and more bitter. Odor-sucrose pairings in sweet likers and dislikers (Experiment 3) found increased sweetness in both groups but increased odor liking only in likers. These data suggest that evaluative and sensory learning are dissociable and that evaluative changes are sensitive to individual differences in sweet liking.
To test whether expression of hedonic and sensory odor qualities acquired by association with sweet and bitter tastes depend on hunger state, hungry volunteers experienced odors paired with sucrose, quinine, or water and then were tested under different hunger states manipulated with energy preloads. Acquired liking for sucrose-paired odors was evident following a low-energy or control preload but not a high-energy preload; however, odor sweetness increased in all preload conditions. Acquired dislike and increased bitterness of quinine-paired odors were independent of preloading. These data demonstrate hunger-dependent expression of acquired liking for flavors through flavor-flavor associations in humans and demonstrate independence between acquired hedonic and sensory qualities of odors.
tries to explain how such a large increase in liking occurs to substances that in the beginning are so aversive / many other foods that are initially only slightly aversive (e.g., many vegetables such as broccoli) never become as liked as do chili pepper and coffee, even though the size of the hedonic shift needed to make them as liked is often smaller / what makes foods such as coffee and chili pepper special
in order to answer that question this paper discusses mechanisms by which hedonic shifts to foods may occur and addresses the possible contribution of these mechanisms to the development of liking for coffee, chili pepper, and broccoli
liking versus preference / factors that change liking [mere exposure, social factors, conditioning (flavor-flavor associations), conditioning (postingestional consequences: calories), conditioning (postingestional consequences: pharmacological), benign masochism, opponent-process, expectations] (PsycINFO Database Record (c) 2012 APA, all rights reserved)
In this study, human Ss (N = 48) were first exposed to a differential evaluative flavor-flavor conditioning schedule, consisting of either 6 or 12 colored CS+ flavor/US compounds and 6 or 12 colored CS− flavor presentations. Two fruit flavors were used as CS+ and CS−, and Tween 20 (Polysorbate 20) was used as a disliked flavor US. The CS− flavor was either presented in plain water or in a moderately positive sugar compound solution. At the moment of testing, visual-analog CS+ and CS− flavor evaluations were obtained in compounds containing the acquisition color, a new color, or no color. The test series was split up in two equivalent logical blocks, allowing to assess the extinction sensitivity of the conditioned flavor valence. A clear acquired evaluative CS+/CS− flavor differentiation was observed when the CS− flavor had been presented in compound with sugar, but only a nonsignificant tendency was obtained when the CS− flavor was presented in plane water. The latter finding was most probably related to the CS−/ water solution not representing a neutral but a mildly negative stimulus. The number of acquisition trials did not influence the size of the conditioning effect, and the test color context did not systematically weaken or strengthen the expression of the acquired evaluative flavor differentiation. Finally, the conditioning effect did not weaken as testing proceeded: An equally strong CS+/CS− differentiation was observed in the second as in the first block of test trials.
When eating or drinking, the individual experiences a multitude of sensations, including taste, smell, touch, temperature, sight, sound, and sometimes pain/irritation. This multi-faceted sensory experience is the underpinning of perceived flavor, although certainly some sensations contribute more than others. This paper reviews how all these sensations interact, both on a perceptual and a physical level, and discusses the resulting impact each has on flavor ratings. Interactions between taste and smell, and interactions of the remaining sensations will be discussed. Finally, practical implications of these interactions for sensory evaluation are discussed.
Pavlovian flavor-flavor associative learning has been suggested as one of the determinants of humans' food likes and dislikes (e.g., Rozin & Zellner, 1985). However, few experimental studies exist which directly examined this proposal. In the present study, the hypothesis was tested that the contingent presentation of a neutral flavor (CS) with an already (dis)liked flavor (US) should result in an increase (or decrease) in liking for the originally neutral flavor. Second, the question was addressed whether or not a perceptual characteristic of food other than its flavor (c.q. its color) may also acquire evaluative value when paired with an appetitive or an aversive flavor US. Finally, the relationship was studied between evaluative conditioning and subjects' explicit knowledge of the stimulus relationships presented during the conditioning phase. In a differential conditioning paradigm, subjects drank 12 compound fluids and 12 CS− fluids. Sugar was used as a positive US, and Tween20 as a negative US, while either the flavor or the color of the drink was scheduled as the CS. As indexed by postconditioning visual analog scale ratings, a strong differential evaluative conditioning effect was observed in the flavor-flavor, negative condition. The evidence for positive flavor-flavor conditioning was weak at best, and no evidence was obtained for color-flavor conditioning. On the other hand, none of the subjects in flavor-flavor groups evidenced any explicit knowledge of the CS-US relation, whereas about half of the color-flavor subjects did so. These results are related to the theoretical issues of positive/negative asymmetry, selective associations, and implicit/explicit knowledge dissociations.
This paper reports a procedure, like classical conditioning, that produces enhancement of liking for flavors by humans. The procedure is “pairing” of a relatively neutral flavor with sugar (a hedonically positive taste). Specifically, subjects drank 24 small samples of flavor A sweetened and 24 small samples of flavor B unsweetened. They were then tested for their liking for flavors A and B, both sweetened and unsweetened. In three different studies, varying in a number of aspects of stimulus presentations and context, a relative enhancement in liking for flavor A appeared both on the day of exposure and 1 week later. An absolute enhancement in liking of flavor B (a “mere exposure” effect) also occurred in two of the three experiments.
Certain odors are routinely described as smelling sweet, This phenomenon may result from the co-occurrence of such odors and tastes outside the laboratory, Experiment 1 tested this possibility by pairing a selected odor with sucrose and another with citric acid in a masked design, using 24-h spaced sessions, preceded and followed by ratings of the odors' taste attributes when sniffed and when rated with tastes in solution, Following conditioning, the odor paired with sucrose smelled sweeter and with citric acid, sourer. In Experiment 2, contingency awareness was examined using a recognition measure, in an otherwise similar design. Again, odors smelled sweeter and sourer postconditioning, Contingency aware and unaware subjects did not differ in performance. Experiment 3 examined an exposure account of these changes, using a similar paradigm to Experiment 1, but with no exposures to sucrose or citric acid. No changes in odor taste attributes were observed, Overall, these findings demonstrate that associative learning, irrespective of awareness, has an important role in the acquisition of odor-taste qualities. (C) 1995 Academic Press, Inc.
In two experiments the smelled sweetness of odors was increased by using them as flavorants of sucrose solution. Experiment 1 used blind experimenters to compare a target odor mixed with sucrose with a control odor mixed with water during masked training trials. The increased sweetness of the target odor was unaffected by whether or not subjects revealed some explicit knowledge of the contingencies in a post-conditioning recognition test. Experiment 2 found that such a conditioned increase in odor sweetness occurred whether training solutions were sipped from a cup or sucked through a straw. Using a frequency test designed to provide a sensitive assay of contingency awareness, there was still no indication that this affected conditioning. It was concluded that such modification of the taste-properties of odors results from implicit simultaneous associative learning and provides an example of learned synesthesia, (C) 1998 Academic Press.
While flavours comprised of simple taste/odour combinations can be easily decomposed, there is evidence that the individual components are seldom perceived independently. Manifestations of interactions include smell/taste confusions, attribution of taste properties such as sweetness or sourness to odours, and the enhancement and suppression of tastes by such odours. These phenomena are probably the result of blurring of the perceptual boundaries of odour and taste properties during repeated pairings as flavours. Following such pairings in the laboratory, odours can be shown to increase in perceived taste properties. It is proposed that during flavour formation, the components are encoded in memory in such a way that a later odour stimulus also elicits taste properties. Sensory properties such as sweetness can thus be seen as cognitive phenomena associated with both tastes and odours, in the latter case residing in memory. However, unlike some odour combinations, flavours, although usually perceived as a functional whole, are not indivisible synthetic entities. Perceptual interactions between odours and tastes are dependent on the extent to which an analytical approach is taken to the measurement of flavour qualities. Thus, odour enhancement of sucrose sweetness is not observed when the intensities of all the components in a flavour are rated. This has been interpreted as a consequence of rating strategies. However, the data are more consistent with a perceptual/cognitive interpretation. Recent research from our lab has shown that the cognitive strategy employed during the pairing of odours and tastes will also determine whether taste/odour interactions occur. The question of how to measure flavour properties is raised by these findings. Whether panellists focus on the sensory source of, for example, sweetness will depend upon the perceptual strategy they adopt. Asking panellists to focus only on the taste sweetness, while possible, may be assuming that odour and taste properties are independent within foods. (C) 1999 Elsevier Science Ltd. All rights reserved.
The effects of metabolic state on sweet perception were measured using a ‘sip-and-spit’ procedure. Subjects rated the intensity
and hedonic value of different sucrose concentrations while sated and while deprived of food for 18 h. The amount of solution
sipped was also measured. The effect of metabolic state changes on sweet reactivity depended upon the subject's underlying
hedonic response to sweet. Subjects could be classified into two major categories: sweet likers (i.e. increasing liking with
increasing concentration) and sweet dislikers (i.e. decreasing liking with increasing concentration). Metabolic state changes
did not alter sweet intensity ratings in either sweet likers or sweet dislikers. For sweet likers, the hedonic value of sweet
did not change across states. In contrast, sweet dislikers showed an attenuated dislike for concentrated sucrose when deprived.
Sweet dislikers also sipped less solution when sated than deprived; sweet likers showed no change. Thus, metabolic state affected
the hedonic value of sweet, and its intake, for only those individuals predisposed to dislike sweet. The relationships among
perceptions of sweet intensity, sweet hedonics, and amount sipped, are discussed.
There was no significant change in flow rates of parotid saliva in nineteen of twenty subjects while they viewed photographs of lemons, or in fourteen of twenty subjects while they cut lemons in a glove box. Neither parotid nor whole-mouth secretion changed from baseline when subjects viewed fresh lemons and lemonade presented in a plastic box. Further, no significant changes in whole-mouth secretion rates were observed when subjects viewed photographs of two appetizing foods, or of fresh doughnuts in a plastic box, even though subjects knew they could eat the doughnuts after the experiment. In most cases, sniffing of the lemons or of the doughnuts resulted in increased flow rates. Subjects demonstrated large differences in their patterns of affective responses to full-strength and diluted lemon juice, which were independent of salivary flow. In the absence of olfactory or tactile stimulations, few subjects altered parotid or whole-mouth secretion rates in response to viewing food or photographs of food. A reevaluation of findings on 'psychic' stimulation of saliva may be in order to ascertain the role of olfactory, tactile, and even trigeminal clues in salivary response to food stimuli.
The majority of individuals can be classified as sweet likers or dislikers based on their hedonic (pleasure) response to sucrose solutions of varying concentrations. Our results indicate that the sweet liker/disliker distinction generalizes to sugars other than sucrose, i.e., glucose and fructose. As well, these individual hedonic response patterns are maintained even when a flavor and color are added to sucrose solutions. However, whether one is a sweet liker or disliker does not predict hedonic response to nonsweet tastes such as salt. These results indicate that the sweet liker/disliker distinction is a robust phenomenon which appears to generalize over, but is restricted to, sweet-tasting substances. The possibility that individual differences in hedonic response may predict preferences for, and intake of, complex tastes characteristic of foods encountered in the real world, is discussed.
It was hypothesised that the hunger-enhancing effects of exposure to the sight and smell of palatable food would disinhibit eating in restrained eaters (self-reported dieters). In two experiments exposure to palatable food stimuli led to increases in motivational (hunger) ratings and salivation, and was followed by overeating in restrained subjects compared with the control condition (no food during exposure) and a condition in which nonpreferred food was presented during the exposure phase. The food intake of unrestrained subjects, on the other hand, was reduced following exposure to palatable food in the first experiment. This shows that breakdown of dietary restraint can be induced by food stimuli even when the food does not constitute a preload. Mere exposure to the sight and smell of palatable food is sufficient to precipitate loss of dieting motivation. The effects of exposure on hunger and salivation were, in general, unrelated to food intake or degree of dietary restraint. Therefore, changes in hunger do not appear to directly mediate increased food intake in dieters. Instead, it is tentatively suggested that anxiety resulting from exposure to liked food may play a role both in disinhibiting eating and suppressing salivation in restrained subjects.
The relative importance of thought, sight, smell, and taste of food in the cephalic phase of gastric acid secretion has not been studied systematically. We found that discussing appetizing food for 30 min (without sight, smell, or taste) increased acid secretion from 4 to 13 mmol/h in healthy human subjects (p less than 0.001) and also increased serum gastrin concentrations significantly (p less than 0.02). Discussing food resulted in an acid secretory response that averaged 66% +/- 10% of the response to modified sham feeding, which activates thought, sight, smell, and taste. Discussing topics other than food (e.g., current events, sports) did not increase acid secretion significantly. The sight of appetizing food (without smell or taste), the smell of appetizing food (without sight or taste), or the combination of sight and smell (without taste) also increased acid secretion and serum gastrin concentrations significantly. However, sight and smell were significantly less potent stimulants of acid secretion than sham feeding, with responses averaging only 23%-46% of the response to sham feeding. These studies indicate that thinking about food is a potent stimulant of gastric secretion in healthy humans. Moreover, the sight and smell of food increase gastric acid secretion and serum gastrin concentrations, probably by provoking thoughts related to food.
Unilateral parotid secretion was determined for 12 Ss using a precision sialometer, in response to the odors of distilled water, three pleasant stimuli (vanillin, β-phenylethanol, anethol), three unpleasant stimuli (pyridine, diethylsulfide, butyric acid), and two irritating stimuli (ethyl alcohol, ammonia). Flow rates were compared with the Ss' rated intensity and affective responses to the same solutions. Flow rates were significantly higher for male than for female Ss, with both secreting significantly more saliva in response to ammonia, ethyl alcohol, and butyric acid, as compared to water. Correlations between flow rates and degree of liking, and between flow rates and rated intensity were not significant.
The purpose of these experiments was to determine whether the level of orally-triggered and vagally-mediated preabsorptive insulin release was related to the degree of food palatability as measured by the amount of food necessary to produce satiation. Rats were habituated to a feeding schedule of five meals per day. During a test meal they were presented with one of 3 forms of their regular diet: unaltered, sweetened with Sucaryl sodium or adulterated with quinine hydrochloride. From 1.5 min preceding the meal to 19.5 min later, blood was continuously drawn via a chronic intravenous catheter. Blood was collected for regular intervals and immunoreactive insulin levels were determined. During the test meals, the rats ate 3, 4.9 and 1.5 g of the three diets, respectively. Within the first 3 min following meal onset, they exhibited a peak insulin release of 47, 65 and 25 microU/ml, respectively. Since this early insulin response disappeared long before the end of the meal, it was suggested that the palatability-dependent amount eaten could be affected by the palatability-modulated preabsorptive insulin release.
To investigate the specificity of satiety in man, subjects (n=32) rated the pleasantness of the taste of eight foods, were then given one of the foods to eat for lunch, and re-rated the pleasantness of the taste of the eight foods 2 and 20 min after the end of the meal. The pleasantness of the food eaten decreased more than that of the foods not eaten (p<0.001). In a second experiment it was shown that this relative specificity of satiety influenced subsequent food intake. Before a first course, subjects (n=24) rated their liking for the taste of eight foods, were then given one of the foods to eat for lunch, and 2 min after finishing eating re-rated their liking for the taste of the eight foods. Again liking decreased more for the food eaten than for foods not eaten. These changes in liking for the foods eaten and not eaten were highly correlated (p<0.001) with the amounts of those foods eaten in an unexpected second course. Thus in man satiety can be partly specific to foods eaten and this specificity may be an important determinant of the foods selected for consumption.
As in the conditioning of appetite for protein in the rat, human preference for and intake of a food at lunch was increased when the flavor of that food was paired with an adequate supply of protein, following a breakfast lacking in protein. Men and women rated their preferences for two flavors in tasted foods (soup and cornflour dessert) on test days before and after a day when one flavor was eaten in very low protein food and another day with a different flavor eaten in food containing protein, but with minimal sensory differences between these foods. Subjects given a low-protein drink preload preferred the protein-paired flavor, while those receiving a high-protein drink did not. In a second experiment, preferences were measured by intake as well as ratings, and the difference in amount of protein between high- and low-protein lunches was increased. By both measures, relative preference for high-protein-paired dessert flavors increased from before to after pairing. The increase in intake preference ratio for the protein-paired flavor was abolished by a high-protein preload. Thus, people have a learning mechanism whereby a lack in protein intake comes to cue the selection of protein-rich foods that are not known to be such, and/or loading with protein might trigger avoidance specifically of a high-protein diet.
To investigate whether children acquire conditioned preferences for flavors associated with high dietary fat content, 27 3- and 4-year-old children participated in a series of 12 conditioning or mere exposure sessions. Following an overnight fast, children who participated in conditioning trials consumed fixed quantities of a flavored yogurt drink that on half the days was high in fat and energy (954 kJ, 18 g fat/150 g serving) or contained no fat (277 kJ, 0 g fat/150 g serving). Children in the conditioning group consumed 150 g servings, children in the mere exposure group tasted 16 g or less of these same stimuli. Preferences were assessed before and after conditioning when the children were hungry and also postconditioning when the children were satiated. Results provided evidence for conditioned preferences based on the postingestive consequences of dietary fat. Children in the conditioning group learned to prefer the high-density paired flavor over the low-density paired flavor, and increased their preference for the high-density paired flavor from pre- to postconditioning. Children in the mere exposure group showed positive shifts in preference for both the fat-free and the high-fat paired flavors. In the conditioning group, preferences for the high-fat flavor was depressed by satiety, whereas the preference of the mere exposure group did not vary with hunger state. Conditioned flavor preferences, based on the postingestive consequences of fat intake, may contribute to children's preferences for foods high in dietary fat.
The human appetite system contains central and peripheral mechanisms that interact with environmental features, especially with the physical and nutrient composition of the food supply. Foods varying in nutrient composition exert different physiologic effects, some of which function as satiety signals. High-fat diets (low food quotient) lead to high levels of energy intake. This effect is termed passive overconsumption and overcomes fat-induced physiological satiety signals. High-fat foods exert a weak effect on satiation (intra-meal satiety), and fat has a weaker effect, joule for joule, on postingestive satiety than do other macronutrients. The frequency of obesity is greater among high-fat than low-fat consumers. However, the development of obesity on a high-fat diet is not a biological inevitability. The investigation of people who resist the weight-inducing properties of high-fat diets is a key research strategy. Understanding the appetite control system suggests behavioral, nutritional, and pharmacologic strategies for modifying dietary fat intake.
It is shown that olfactory sensory-specific satiety, measured by ratings of the pleasantness of the odour of a food eaten relative to the change in pleasantness of other foods, can be produced by eating a food to satiety. It is also shown that olfactory and taste sensory-specific satiety can be produced by chewing samples of a food for approximately as long as the food would normally be eaten in a meal. It is further shown that partial olfactory sensory-specific satiety can be produced by smelling the food for approximately as long as it would be in the mouth during a meal. These sensory-specific changes in the pleasantness of a food do not appear to reflect changes in the intensity of the foods, which were small and not highly correlated with the changes in pleasantness. The results show that at least partial olfactory, as well as taste, sensory-specific satiety does not require food to enter the gastrointestinal system, and does not depend on the ingestion of calories. The implications for the control of food intake, and the way in which the brain computes sensory-specific satiety, are considered.