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Physiological Reviews Jan 2023Taste and smell play a key role in our ability to perceive foods. Overconsumption of highly palatable energy-dense foods can lead to increased caloric intake and... (Review)
Review
Taste and smell play a key role in our ability to perceive foods. Overconsumption of highly palatable energy-dense foods can lead to increased caloric intake and obesity. Thus there is growing interest in the study of the biological mediators of fat taste and associated olfaction as potential targets for pharmacologic and nutritional interventions in the context of obesity and health. The number of studies examining mechanisms underlying fat taste and smell has grown rapidly in the last 5 years. Therefore, the purpose of this systematic review is to summarize emerging evidence examining the biological mechanisms of fat taste and smell. A literature search was conducted of studies published in English between 2014 and 2021 in adult humans and animal models. Database searches were conducted using PubMed, EMBASE, Scopus, and Web of Science for key terms including fat/lipid, taste, and olfaction. Initially, 4,062 articles were identified through database searches, and a total of 84 relevant articles met inclusion and exclusion criteria and are included in this review. Existing literature suggests that there are several proteins integral to fat chemosensation, including cluster of differentiation 36 (CD36) and G protein-coupled receptor 120 (GPR120). This systematic review will discuss these proteins and the signal transduction pathways involved in fat detection. We also review neural circuits, key brain regions, ingestive cues, postingestive signals, and genetic polymorphism that play a role in fat perception and consumption. Finally, we discuss the role of fat taste and smell in the context of eating behavior and obesity.
Topics: Animals; Humans; Feeding Behavior; Obesity; Smell; Taste; Taste Buds
PubMed: 36409650
DOI: 10.1152/physrev.00061.2021 -
Ageing Research Reviews Sep 2021Alterations in olfactory functions are proposed to be early biomarkers for neurodegeneration. Many neurodegenerative diseases are age-related, including two of the most... (Review)
Review
Alterations in olfactory functions are proposed to be early biomarkers for neurodegeneration. Many neurodegenerative diseases are age-related, including two of the most common, Parkinson's disease (PD) and Alzheimer's disease (AD). The establishment of biomarkers that promote early risk identification is critical for the implementation of early treatment to postpone or avert pathological development. Olfactory dysfunction (OD) is seen in 90% of early-stage PD patients and 85% of patients with early-stage AD, which makes it an attractive biomarker for early diagnosis of these diseases. Here, we systematically review widely applied smelling tests available for humans as well as olfaction assessments performed in some animal models and the relationships between OD and normal aging, PD, AD, and other conditions. The utility of OD as a biomarker for neurodegenerative disease diagnosis and future research directions are also discussed.
Topics: Aging; Alzheimer Disease; Animals; Humans; Neurodegenerative Diseases; Olfaction Disorders; Parkinson Disease; Smell
PubMed: 34325072
DOI: 10.1016/j.arr.2021.101416 -
The Cochrane Database of Systematic... Nov 2022Perception is the ability to understand information from our senses. It allows us to experience and meaningfully interact with our environment. A stroke may impair... (Review)
Review
BACKGROUND
Perception is the ability to understand information from our senses. It allows us to experience and meaningfully interact with our environment. A stroke may impair perception in up to 70% of stroke survivors, leading to distress, increased dependence on others, and poorer quality of life. Interventions to address perceptual disorders may include assessment and screening, rehabilitation, non-invasive brain stimulation, pharmacological and surgical approaches.
OBJECTIVES
To assess the effectiveness of interventions aimed at perceptual disorders after stroke compared to no intervention or control (placebo, standard care, attention control), on measures of performance in activities of daily living. SEARCH METHODS: We searched the trials registers of the Cochrane Stroke Group, CENTRAL, MEDLINE, Embase, and three other databases to August 2021. We also searched trials and research registers, reference lists of studies, handsearched journals, and contacted authors.
SELECTION CRITERIA
We included randomised controlled trials (RCTs) of adult stroke survivors with perceptual disorders. We defined perception as the specific mental functions of recognising and interpreting sensory stimuli and included hearing, taste, touch, smell, somatosensation, and vision. Our definition of perception excluded visual field deficits, neglect/inattention, and pain.
DATA COLLECTION AND ANALYSIS
One review author assessed titles, with two review authors independently screening abstracts and full-text articles for eligibility. One review author extracted, appraised, and entered data, which were checked by a second author. We assessed risk of bias (ROB) using the ROB-1 tool, and quality of evidence using GRADE. A stakeholder group, comprising stroke survivors, carers, and healthcare professionals, was involved in this review update.
MAIN RESULTS
We identified 18 eligible RCTs involving 541 participants. The trials addressed touch (three trials, 70 participants), somatosensory (seven trials, 196 participants) and visual perception disorders (seven trials, 225 participants), with one (50 participants) exploring mixed touch-somatosensory disorders. None addressed stroke-related hearing, taste, or smell perception disorders. All but one examined the effectiveness of rehabilitation interventions; the exception evaluated non-invasive brain stimulation. For our main comparison of active intervention versus no treatment or control, one trial reported our primary outcome of performance in activities of daily living (ADL): Somatosensory disorders: one trial (24 participants) compared an intervention with a control intervention and reported an ADL measure. Touch perception disorder: no trials measuring ADL compared an intervention with no treatment or with a control intervention. Visual perception disorders: no trials measuring ADL compared an intervention with no treatment or control. In addition, six trials reported ADL outcomes in a comparison of active intervention versus active intervention, relating to somatosensation (three trials), touch (one trial) and vision (two trials). AUTHORS' CONCLUSIONS: Following a detailed, systematic search, we identified limited RCT evidence of the effectiveness of interventions for perceptual disorders following stroke. There is insufficient evidence to support or refute the suggestion that perceptual interventions are effective. More high-quality trials of interventions for perceptual disorders in stroke are needed. They should recruit sufficient participant numbers, include a 'usual care' comparison, and measure longer-term functional outcomes, at time points beyond the initial intervention period. People with impaired perception following a stroke should continue to receive neurorehabilitation according to clinical guidelines.
Topics: Adult; Humans; Activities of Daily Living; Perceptual Disorders; Stroke; Stroke Rehabilitation; Vision Disorders; Randomized Controlled Trials as Topic
PubMed: 36326118
DOI: 10.1002/14651858.CD007039.pub3 -
European Eating Disorders Review : the... Sep 2022The aim of this study was to assess the relationship between sensory processing and a broad range of eating behaviours across the lifespan. (Review)
Review
OBJECTIVES
The aim of this study was to assess the relationship between sensory processing and a broad range of eating behaviours across the lifespan.
METHODS
Five electronic databases of published and unpublished quantitative studies were systematically searched, evaluated for risk of bias and synthesised according to identified eating outcomes.
RESULTS
Across 25 studies, there was consistent evidence of a relationship between sensory processing and a range of eating behaviours. There was early evidence for the particular role of taste/smell sensitivities, as well as hypersensitivities, although future research is needed looking at different sensory patterns and modalities. There was also tentative evidence to suggest this relationship extends across development.
DISCUSSION
Study findings are discussed in relation to implications for sensory-based eating and feeding interventions and the development of eating disorders. Methodological and conceptual limitations are discussed and suggestions for future research are made to address these limitations. A broader investigation of multi-sensory issues and clearly defined eating behaviours, including disordered eating in clinically diagnosed samples, will allow for a more comprehensive and robust understanding of the relationship between sensory processing and eating behaviours in autism.
Topics: Autistic Disorder; Feeding Behavior; Feeding and Eating Disorders; Humans; Perception; Taste
PubMed: 35737818
DOI: 10.1002/erv.2920 -
Neuropsychology Review Mar 2024Olfactory training (OT), or smell training,consists of repeated exposure to odorants over time with the intended neuroplastic effect of improving or remediating... (Review)
Review
Olfactory training (OT), or smell training,consists of repeated exposure to odorants over time with the intended neuroplastic effect of improving or remediating olfactory functioning. Declines in olfaction parallel declines in cognition in various pathological conditions and aging. Research suggests a dynamic neural connection exists between olfaction and cognition. Thus, if OT can improve olfaction, could OT also improve cognition and support brain function? To answer this question, we conducted a systematic review of the literature to determine whether there is evidence that OT translates to improved cognition or altered brain morphology and connectivity that supports cognition. Across three databases (MEDLINE, Scopus, & Embase), 18 articles were identified in this systematic review. Overall, the reviewed studies provided emerging evidence that OT is associated with improved global cognition, and in particular, verbal fluency and verbal learning/memory. OT is also associated with increases in the volume/size of olfactory-related brain regions, including the olfactory bulb and hippocampus, and altered functional connectivity. Interestingly, these positive effects were not limited to patients with smell loss (i.e., hyposmia & anosmia) but normosmic (i.e., normal ability to smell) participants benefitted as well. Implications for practice and research are provided.
Topics: Humans; Brain; Cognition; Olfaction Disorders; Olfactory Training; Smell
PubMed: 36725781
DOI: 10.1007/s11065-022-09573-0 -
Chemical Senses Jan 2022Little attention has been paid to olfactory changes during pregnancy with contemporary studies limited in number and sample size. We examined whether pregnancy is... (Meta-Analysis)
Meta-Analysis
Little attention has been paid to olfactory changes during pregnancy with contemporary studies limited in number and sample size. We examined whether pregnancy is associated with differences in olfactory performance and if there were any specific gestational ages at which these differences occur through a comprehensive systematic review and meta-analysis of the current literature. An initial electronic database search identified 234 citations, which were screened at the abstract level. Twenty-three citations were germane for full-text review, and 13 met criteria for inclusion. Our review assessed 5 olfactory measures of interest: odor identification (n = 11 articles), threshold (n = 8), discrimination (n = 5), hedonics (n = 6), and intensity (n = 5). Nine of these 13 studies contained sufficient data for meta-analysis, and these studies included a total of 523 pregnant women and 365 non-pregnant controls. Despite previous subjective and objective reports of odor intolerances and odor hypersensitivity, we did not find any significant differences between pregnant and non-pregnant women in odor discrimination, thresholds, or hedonics. However, meta-analysis of 506 cases and 333 controls showed worse odor identification in pregnant women compared to controls in a random-effects model. Thus, we demonstrate worse performance at odor identification during pregnancy. In this review, we discuss the current evidence (and lack thereof) regarding olfaction in pregnancy as well as highlight current knowledge gaps in this field.
Topics: Pregnancy; Humans; Female; Smell; Odorants; Olfaction Disorders
PubMed: 36469055
DOI: 10.1093/chemse/bjac035 -
The Cochrane Database of Systematic... Mar 2021This living systematic review is one of several Cochrane Reviews evaluating the medical management of patients with chronic rhinosinusitis. Chronic rhinosinusitis is... (Meta-Analysis)
Meta-Analysis
BACKGROUND
This living systematic review is one of several Cochrane Reviews evaluating the medical management of patients with chronic rhinosinusitis. Chronic rhinosinusitis is common. It is characterised by inflammation of the nasal and sinus linings, nasal blockage, rhinorrhoea, facial pressure/pain and loss of sense of smell. It occurs with or without nasal polyps. 'Biologics' are medicinal products produced by a biological process. Monoclonal antibodies are one type, already evaluated in other inflammatory conditions (e.g. asthma and atopic dermatitis).
OBJECTIVES
To assess the effects of biologics for the treatment of chronic rhinosinusitis.
SEARCH METHODS
The Cochrane ENT Information Specialist searched the Cochrane ENT Register; CENTRAL (2020, Issue 9); Ovid MEDLINE; Ovid Embase; Web of Science; ClinicalTrials.gov; ICTRP and additional sources for published and unpublished studies. The date of the search was 28 September 2020.
SELECTION CRITERIA
Randomised controlled trials (RCTs) with at least three months follow-up comparing biologics (monoclonal antibodies) against placebo/no treatment in patients with chronic rhinosinusitis.
DATA COLLECTION AND ANALYSIS
We used standard Cochrane methodological procedures. Our primary outcomes were disease-specific health-related quality of life (HRQL), disease severity and serious adverse events (SAEs). The secondary outcomes were avoidance of surgery, extent of disease (measured by endoscopic or computerised tomography (CT) score), generic HRQL and adverse effects (nasopharyngitis, including sore throat). We used GRADE to assess the certainty of the evidence for each outcome.
MAIN RESULTS
We included 10 studies. Of 1262 adult participants, 1260 had severe chronic rhinosinusitis with nasal polyps; 43% to 100% of participants also had asthma. Three biologics, with different targets, were evaluated: dupilumab, mepolizumab and omalizumab. All of the studies were sponsored or supported by industry. For this update (2021) we have included two new studies, including 265 participants, which reported data relating to omalizumab. Anti-IL-4Rα mAb (dupilumab) versus placebo/no treatment (all receiving intranasal steroids) Three studies (784 participants) evaluated dupilumab. Disease-specific HRQL was measured with the SNOT-22 (a 22-item questionnaire, with a score range of 0 to 110; minimal clinically important difference (MCID) 8.9 points). At 24 weeks, dupilumab results in a large reduction (improvement) in the SNOT-22 score (mean difference (MD) -19.61, 95% confidence interval (CI) -22.54 to -16.69; 3 studies; 784 participants; high certainty). At between 16 and 52 weeks of follow-up, dupilumab probably results in a large reduction in disease severity, as measured by a 0- to 10-point visual analogue scale (VAS) (MD -3.00, 95% CI -3.47 to -2.53; 3 studies; 784 participants; moderate certainty). This is a global symptom score, including all aspects of chronic rhinosinusitis symptoms. At between 16 and 52 weeks of follow-up, dupilumab may result in a reduction in serious adverse events compared to placebo (5.9% versus 12.5%, risk ratio (RR) 0.47, 95% CI 0.29 to 0.76; 3 studies, 782 participants; low certainty). Anti-IL-5 mAb (mepolizumab) versus placebo/no treatment (all receiving intranasal steroids) Two studies (137 participants) evaluated mepolizumab. Disease-specific HRQL was measured with the SNOT-22. At 25 weeks, the SNOT-22 score may be reduced (improved) in participants receiving mepolizumab (MD -13.26 points, 95% CI -22.08 to -4.44; 1 study; 105 participants; low certainty; MCID 8.9). It is very uncertain whether there is a difference in disease severity at 25 weeks: on a 0- to 10-point VAS, disease severity was -2.03 lower in those receiving mepolizumab (95% CI -3.65 to -0.41; 1 study; 72 participants; very low certainty). It is very uncertain if there is a difference in the number of serious adverse events at between 25 and 40 weeks (1.4% versus 0%; RR 1.57, 95% CI 0.07 to 35.46; 2 studies; 135 participants, very low certainty). Anti-IgE mAb (omalizumab) versus placebo/no treatment (all receiving intranasal steroids) Five studies (329 participants) evaluated omalizumab. Disease-specific HRQL was measured with the SNOT-22. At 24 weeks omalizumab probably results in a large reduction in SNOT-22 score (MD -15.62, 95% CI -19.79 to -11.45; 2 studies; 265 participants; moderate certainty; MCID 8.9). We did not identify any evidence for overall disease severity. It is very uncertain whether omalizumab affects the number of serious adverse events, with follow-up between 20 and 26 weeks (0.8% versus 2.5%, RR 0.32, 95% CI 0.05 to 2.00; 5 studies; 329 participants; very low certainty).
AUTHORS' CONCLUSIONS
Almost all of the participants in the included studies had nasal polyps (99.8%) and all were using topical nasal steroids for their chronic rhinosinusitis symptoms. In these patients, dupilumab improves disease-specific HRQL compared to placebo. It probably also results in a reduction in disease severity, and may result in a reduction in the number of serious adverse events. Mepolizumab may improve disease-specific HRQL. It is very uncertain if there is a difference in disease severity or the number of serious adverse events. Omalizumab probably improves disease-specific HRQL compared to placebo. It is very uncertain if there is a difference in the number of serious adverse events. There was no evidence regarding the effect of omalizumab on disease severity (using global scores that address all symptoms of chronic rhinosinusitis).
Topics: Adult; Anti-Allergic Agents; Antibodies, Monoclonal, Humanized; Bias; Biological Products; Chronic Disease; Humans; Nasal Obstruction; Nasal Polyps; Omalizumab; Placebos; Quality of Life; Randomized Controlled Trials as Topic; Rhinitis; Sinusitis; Treatment Outcome
PubMed: 33710614
DOI: 10.1002/14651858.CD013513.pub3 -
Chemical Senses Jul 2016Previous studies on the relationship between olfaction and depression have revealed mixed results. In addition, few have focused on the reciprocity of this association.... (Review)
Review
Previous studies on the relationship between olfaction and depression have revealed mixed results. In addition, few have focused on the reciprocity of this association. The aim of this study is to combine depression and olfactory data in two separate patient populations to further understand their association. A systematic literature review was conducted using 3 online databases to identify studies correlating olfaction and depression in patients presenting with either primary depression or primary olfactory dysfunction. For the depressed population, weighted means and standard deviations for the Sniffin' Sticks Test and the 40-item Smell Identification Test were combined using 10 studies. For the olfactory dysfunction population, weighted means of Beck's Depression Inventory were combined using 3 studies. Independent t-tests were used to compare differences between groups. Comparing primary depressed patients with controls, depressed patients showed decreased scores in olfactory threshold (6.31±1.38 vs. 6.78±0.88, P = 0.0005), discrimination (12.05±1.44 vs. 12.66±1.36, P = 0.0073), identification (12.57±0.74 vs. 12.98±0.90, P < 0.0001), and 40-Item Smell Identification Test (35.31±1.91 vs. 37.41±1.45, P < 0.0001). In patients with primary olfactory dysfunction, Beck's Depression Inventory scores were significantly different between patients classified as normosmics, hyposmics and anosmics (5.21±4.73 vs. 10.93±9.25 vs. 14.15±5.39, P ≤ 0.0274 for all 3 comparisons). In conclusion, patients with depression have reduced olfactory performance when compared with the healthy controls and conversely, patients with olfactory dysfunction, have symptoms of depression that worsen with severity of smell loss.
Topics: Depressive Disorder; Humans; Olfaction Disorders; Sensory Thresholds; Smell
PubMed: 27170667
DOI: 10.1093/chemse/bjw061 -
Frontiers in Psychology 2022Objective tests of olfaction are widely available to aid in the assessment of olfaction. Their clearest role is in the characterization of olfactory changes, either...
Objective tests of olfaction are widely available to aid in the assessment of olfaction. Their clearest role is in the characterization of olfactory changes, either reported by or suspected in a patient. There is a rapidly growing literature concerned with the association of olfactory changes with certain neuropsychiatric conditions and the use of olfactory testing to supplement conventional assessments in clinical and research practice is evolving. Neural pathways important for olfactory processing overlap extensively with pathways important for cognitive functioning, and especially those important for executive functioning, many of which are concentrated in the frontal lobes. Previous work has identified associations between performance on certain olfactory tests (most frequently olfactory identification) and executive functioning and behavioral measures (e.g. of impulsivity). More recently, similar associations have also been identified in non-clinical samples, raising new questions as to the utility of olfactory test scores as proxy measures for non-olfactory phenomena. In this systemic review, we sought to identify studies, both clinical and non-clinical, that investigated the associations of olfaction with performance on tasks sensitive to frontal lobe functioning. Our search criteria led to the identification of 70 studies published in English. We examined in detail and tabulated the data from these studies, highlighted each study's key findings, and critically evaluated these studies. We use the results of this review to reflect on some of the current and future challenges concerning the use of olfactory testing in clinical neuropsychiatric practice and research and speculate on the potential benefits of administering phonemic fluency in combination with olfactory testing to enhance its predictive value.
PubMed: 35615205
DOI: 10.3389/fpsyg.2022.871391 -
Frontiers in Psychology 2015The study provides a systematic review that explores the current literature on olfactory capacity in abnormal eating behavior. The objective is to present a basis for... (Review)
Review
The study provides a systematic review that explores the current literature on olfactory capacity in abnormal eating behavior. The objective is to present a basis for discussion on whether research in olfaction in eating disorders may offer additional insight with regard to the complex etiopathology of eating disorders (ED) and abnormal eating behaviors. Electronic databases (Medline, PsycINFO, PubMed, Science Direct, and Web of Science) were searched using the components in relation to olfaction and combining them with the components related to abnormal eating behavior. Out of 1352 articles, titles were first excluded by title (n = 64) and then by abstract and fulltext resulting in a final selection of 14 articles (820 patients and 385 control participants) for this review. The highest number of existing literature on olfaction in ED were carried out with AN patients (78.6%) followed by BN patients (35.7%) and obese individuals (14.3%). Most studies were only conducted on females. The general findings support that olfaction is altered in AN and in obesity and indicates toward there being little to no difference in olfactory capacity between BN patients and the general population. Due to the limited number of studies and heterogeneity this review stresses on the importance of more research on olfaction and abnormal eating behavior.
PubMed: 26483708
DOI: 10.3389/fpsyg.2015.01431