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In all graphs: Error bars denote standard deviation, and stars above bar denotes results significantly different from expected chance performance (33.3%, p <.05). S = skim milk, M = medium milk, F = fat milk. See Methods section for further details regarding fat percentage. SM = discriminating between skim and medium milk; MF = discriminating between medium and fat milk; SF = discriminating between skim and fat milk. Dotted line in panel A, B, & C indicates expected chance performance (33.3%). A) Results of Experiment 1 in a North-American population. B) Results of Experiment 2 in a Dutch population. C) Results of Experiment 3 including normal-weight (black bars) and overweight individuals (white bars). D) Relationship between total discrimination performance and average daily dairy fat intake (in grams). Solid line in graph represents the regression line.
Source publication
The desire to consume high volumes of fat is thought to originate from an evolutionary pressure to hoard calories, and fat is among the few energy sources that we can store over a longer time period. From an ecological perspective, however, it would be beneficial to detect fat from a distance, before ingesting it. Previous results indicate that hum...
Citations
... 31 For instance, we have retained a good ability to assess fat content in food via odor cues, an advantageous adaptation for our ancestors to ensure they would ingest the highest quality and most caloric food. 118 F I G U R E 2 Odors emitted and olfactory ability changes across the life course. Some roles of olfaction, such as the disgust response to rotten food, remain rather consistent throughout life, while others develop at certain points in life, such as the arousal response to sexual odors starting at the onset of puberty. ...
The sense of smell is an important mediator of health and sociality at all stages of life, yet it has received limited attention in our lineage. Olfaction starts in utero and participates in the establishment of social bonds in children, and of romantic and sexual relationships after puberty. Smell further plays a key role in food assessment and danger avoidance; in modern societies, it also guides our consumer behavior. Sensory abilities typically decrease with age and can be impacted by diseases, with repercussions on health and well‐being. Here, we critically review our current understanding of human olfactory communication to refute outdated notions that our sense of smell is of low importance. We provide a summary of the biology of olfaction, give a prospective overview of the importance of the sense of smell throughout the life course, and conclude with an outline of the limitations and future directions in this field.
... However, descriptions of human olfaction of fats, including the nasal mediators responsible for fat detection and discrimination, are nearly absent, illustrating that little is known about human fat olfaction. A few studies have demonstrated our ability to detect fat content in foods (i.e., cow milk) from a distance, plausibly via the olfactory system (Boesveldt and Lundström 2014;Mu et al. 2022). However, the results failed to demonstrate an olfactory sense of fat per se. ...
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.
... Humans can detect fatty acids (linoleic, oleic, and stearic acid), both orthonasally and retronasally (Bolton & Halpern, 2010). Humans can retronasally detect the presence of fat in milks (Le Calvé et al., 2015) and discriminate between different concentrations of fat in milk (0, 1.5 and 3.5%) based on orthonasal smell (Boesveldt & Lundstrom, 2014). Descriptive sensory analysis of margarines showed that with increasing fat content, butter and cheese odor intensity increased while creamy odor intensity decreased (Dadalı & Elmacı, 2019). ...
... To the best of our knowledge, this is the first study that compared olfactory fat discrimination in pasteurized and UHT milks. Boesveldt and Lundstrom (2014) previously reported that humans can orthonasally detect difference in fat content of reconstituted milks. Pirc et al. (2022) confirmed these findings in manipulated milks differing in fat content (milks prepared with different mixing ratios of either milk powder and water or cream and skim milk) and reported that humans are also capable of discriminating fat content of milks solely based on retronasal olfaction. ...
... Thus, our findings suggest that consumers can, based on smell only, discriminate the milks that are consumed globally the most. We observed that the ability to olfactorily discriminate between milks differing in fat content was not affected by demographics nor dairy consumption habits, which is in line with previous studies (Boesveldt & Lundstrom, 2014;Pirc et al., 2022). However, for non-dairy foods, Kindleysides et al. (2017) observed that consumers who have higher intake of seeds, nuts and nut spreads are more sensitive to detect the smell of oleic acid. ...
The mechanisms underlying the ability of humans to olfactorily discriminate fat content in milks remain unknown. In this study, we found that fat contents (0.5, 1.5 and 3.5% fat) can be discriminated by olfaction in commercially available pasteurized milks (p < 0.05) but not in ultra-high temperature processed (UHT) milks. The composition of volatile compounds of pasteurized milks differed with fat content, whereas that of UHT milks differing in fat content was similar. Principal component analysis revealed that differences in volatile compound composition of pasteurized milks differing in fat content contribute to olfactory discrimination. In UHT milks, acetoin and 2-heptanone may mask odor differences leading to indistinguishable odors. No differences were observed regarding perceived odor intensity of pasteurized milks or UHT milks differing in fat content. We conclude that the olfactory discrimination of fat content in pasteurized milks is facilitated by differences in volatile compound composition rather than odor intensity.
... In addition, food odors can accurately reflect nutritional information such as the caloric density and main macronutrient content of food (10). For example, people can distinguish fat content of foods from odors (11) and can classify food items with the "taste" (e.g., sweet or nonsweet) or energy density (e.g., high or low energy density) (12). Food odors compared with nonfood odors were shown to activate both olfactory and rewardrelated brain regions, such as the piriform cortex, amygdala, orbitofrontal cortex, ventromedial prefrontal cortex, insula, ventral striatum, and anterior cingulate cortex (13)(14)(15). ...
Objective
Food odors serve as powerful stimuli signaling the food quality and energy density and direct food‐specific appetite and consumption. This study explored obesity‐related brain activation in response to odors related to high‐ or low‐energy‐dense foods.
Methods
Seventeen participants with obesity (BMI > 30 kg/m²; 4 males and 13 females) and twenty‐one with normal weight (BMI < 25 kg/m²; 9 males and 12 females) underwent a functional magnetic resonance imaging scan in which they received chocolate (high‐energy‐dense food) and cucumber (low‐energy‐dense food) odor stimuli. Participants’ olfactory and gustatory functions were assessed by the “Sniffin’ Sticks” and “Taste Strips” tests, respectively.
Results
Compared with normal‐weight controls, participants with obesity had lower odor sensitivity (phenylethyl alcohol) and decreased odor discrimination ability. However, participants with obesity demonstrated greater brain activation in response to chocolate compared with cucumber odors in the bilateral inferior frontal operculum and cerebellar vermis, right ventral anterior insula extending to putamen, right middle temporal gyrus, and right supramarginal areas.
Conclusions
The present study provides preliminary evidence that obesity is associated with heightened brain activation of the reward and flavor processing areas in response to chocolate versus cucumber odors, possibly because of the higher energy density and reinforcing value of chocolate compared with cucumber.
... 7,92 Behavioral uses of olfactory cues and signals vary across primate species but all primates use olfaction for odor quality perception and share a general dietary bias for calorically dense food, 93 which may be mediated partly by odor cues. 94 Like other big-brained primates, humans require calorically dense food for adequate energy. 95 We use odor cues from foods to identify fats, which have more than twice the amount of energy as other macronutrients and require minimal energy to digest. ...
... 95 We use odor cues from foods to identify fats, which have more than twice the amount of energy as other macronutrients and require minimal energy to digest. 96,94 We also cook our food (as did other members of our genus), 97 which increases food digestion and stimulates the olfactory system. Most captive apes prefer cooked food when given a choice, which suggests a shared preference for foods with higher nutritional quality that are easy to chew. ...
Anthropogenic disruptions to animal sensory ecology are as old as our species. But what about the effect on human sensory ecology? Human sensory dysfunction is increasing globally at great economic and health costs (mental, physical, and social). Contemporary sensory problems are directly tied to human behavioral changes and activity as well as anthropogenic pollution. The evolutionary sensory ecology and anthropogenic disruptions to three human senses (vision, audition, olfaction) are examined along with the economic and health costs of functionally reduced senses and demographic risk factors contributing to impairment. The primary goals of the paper are (a) to sew an evolutionary and ecological thread through clinical narratives on sensory dysfunction that highlights the impact of the built environment on the senses, and (b) to highlight structural, demographic, and environmental injustices that create sensory inequities in risk and that promote health disparities.
... Because nutrients and fats in food are registered by chemosensation before any other sensory modality (Julliard et al., 2017;Boesveldt and Lundströ m, 2014), smell, texture, and taste are vital for appetite regulation (Soria-Gó mez et al., 2014) and HFD preference formation (Sørensen et al., 2003). Real-time recordings of population dynamics from orexigenic agouti-related peptide (AgRP) or anorectic proopiomelanocortin (POMC) neurons reveal rapid inhibition or activation, respectively, to hidden peanut butter (Chen et al., 2015), suggesting that the smell of food quickly modulates the firing properties of key feeding regulators before nutrients are tasted or consumed. ...
... Olfaction is not required for home-cage HFD preference or SD devaluation Because chemosensory cues serve as essential indicators for food foraging and appreciation (Sørensen et al., 2003;Julliard et al., 2017;Boesveldt and Lundströ m, 2014), we hypothesized that anosmia may reduce acute and/or chronic preference toward HFD consumption. Mice underwent either a sham surgery or a procedure involving the complete bilateral removal of the olfactory bulb ( Figure 3A). ...
Obesity is frequently caused by calorie-rich dietary choices across the animal kingdom. As prandial preference toward a high-fat diet develops in mice, an anti-preference or devaluation of a nutritionally balanced but less palatable standard chow diet occurs concomitantly. Although mechanistic insights underlying devaluation have been observed physiologically in the brain, it is unclear how peripheral sensory processing affects food choice. Because olfactory cues and odor perception help coordinate food preference and intake, we determine the role of smell in the targeted consumption of a high-fat diet and simultaneous devaluation of a standard chow diet. Using inaccessible food and loss-of-function manipulations, we find that olfactory information is neither sufficient nor necessary for both the acute and chronic selection of high-fat diet and coincident diminished value of standard diet. This work suggests alternative means are behind the immediate and sustained consumption of high-fat diet and concurrent standard diet devaluation.
... It follows that the spatial processing bias is unlikely to discriminate between completely novel foods, unless the differential energy return rates of such foods are to be readily detected prior to ingestion (e.g. smelling fat content from a distance; Boesveldt & Lundström, 2014) or shortly after tasting (e.g. Smeets et al., 2011). ...
... Increasing evidence suggests that humans can detect the fat content of foods through smells and taste, thus perception of fat taste, aroma, and texture is proposed to influence food preferences [23,43,44]. Moreover, the chemoreception of FA seems to implicate different types of lipid sensors [45]. ...
A taste component is implicated in the oro-sensory detection of dietary lipids and free fatty acids seem to be involved in fatty food recognition. Bottarga, the salted and semi-dried ovary product of mullet (Mugil spp.), is a rich-fat food. A comparative sensory assessment of different commercial bottarga samples was performed in insect and human models in relation to their lipid composition. The bottarga attractant effect to Ceratitis capitata was assessed by behavioral tests. The subjective odor and taste perception of bottarga samples was investigated in human determining the rate of pleasantness, familiarity, and intensity dimensions using the 7-points Likert-type scale. Bottarga samples showed similar lipid profiles, but differences emerged in total and free fatty acid levels. Significant differences were observed in the attractant effect/acceptability of samples to medflies, negatively correlated to their total and free fatty acids. Insect female exhibited the ability to select among bottarga samples based on their visual and olfactory properties. In the human model, a potential contribution of free fatty acid amount in the pleasantness and familiarity dimensions of taste of bottarga samples was evidenced. Women exhibited a greater ability than men to select bottarga samples based on their better olfactory perception. Our results increase the knowledge about this outstanding product with nutritional and nutraceutical properties.
... For example, sweet food odors usually emanate from food high in sugar content. In addition, through orthonasal olfaction, humans can discriminate high concentrations of long-chain fatty acids in vapor phase (Bolton and Halpern, 2010) and were able to discriminate between skimmed, medium, and full fat milk samples with an overall accuracy of 40-55% correct trials in three consecutive experiments, a value that is significantly above the expected chance level (33.3%) (Boesveldt and Lundstrom, 2014). Thus, the orthonasal olfaction may function as a detection system for nutrients content within natural food sources. ...
... Asterisks denote statistically significant differences (*p < 0.05). gl, glomerular layer; gr, granular layer; opl, outer plexiform layer; ml, mitral layer; ipl, inner plexiform layer; onl, olfactory nerve layer mediated regulation of appetite for high-fat foods has been extensively studied in animal models and in human [26][27][28][29], even though no great progresses have been made in defining how much genetic background might impact on individual eating-related chemosensory landscape [30]. Prep1/Pknox1 transcription factor has been widely investigated in our previous studies as an important regulator of metabolic homeostasis, as Prep1-deficient mouse model displays better insulin sensitivity and a reduced risk of developing diabetes and diabetes-related comorbidities [11][12][13][14]. ...
Prep1 is a homeodomain transcription factor which has an important role in hindbrain development. Prep1 expression is also kept in adult mouse brain and in particular within the olfactory bulbs. Moreover, many Prep1 neurons co-localize with Calbindin-positive periglomerular interneurons in olfactory glomerular layer. However, Prep1 function in this brain region is still unknown. In this study, we show that Prep1 hypomorphic heterozygous (Prep1i/+) mice express low levels of protein and feature a 30% reduction of olfactory bulb area, compared to WT mice. In addition, Prep1i/+ mice olfactory bulb histological analysis indicated a 20% lower cytochrome C oxidase activity within the glomerular layer, accompanied by a reduced number of periglomerular interneurons, compared to the WT littermates. Consistently, olfactory perception test highlighted that Prep1 hypomorphic heterozygous mice display a scant ability to distinguish odors, which significantly impacts on feeding behavior, as Prep1i/+ mice revealed a reduced preference for high-fat food. Analysis of BDNF signaling, which represents the main molecular mediator of olfactory plasticity, showed that Prep1i/+ mouse olfactory bulbs feature a 30% reduction of TrkB receptor levels and a decreased activation of ERK1/2. Similarly, overexpression of Prep1 in mouse neuronal cells (N2A) caused an increase of TrkB expression levels, BDNF-induced ERK phosphorylation, and cell viability, compared to control cells. We conclude that Prep1 deficiency alters olfactory morpho-functional integrity and olfaction-mediated eating behavior by affecting BDNF-TrkB signaling. Prep1 could, therefore, play a crucial role in behavioral dysfunctions associated to impaired responsiveness to BDNF.
Electronic supplementary material
The online version of this article (10.1007/s12035-018-0873-7) contains supplementary material, which is available to authorized users.
