COVID-19: Identifying The Scientific Methodologies Behind a Displaced Palate

I received a few requests to publish my research paper from last semester’s Advanced Food class, which I took as part of my graduate studies in Food Studies at New York University. It explores essential oils in retraining your accessory olfactory pathways. Feel free to reach out with questions or comments.

COVID-19: Identifying The Scientific Methodologies Behind a Displaced Palate

Introduction

The COVID-19 pandemic indelibly shapeshifted many thoughts around food.  Being personally fortunate enough to maintain typical eating habits centered around sourcing ethically-curated, whole food ingredients, the past few years have still transformed my individual viewpoints on utilizing food more as a form of advocacy and nourishment, rather than a source of entertainment and pleasure. As I complete my master’s candidacy in Food Studies, extending aid to those going through food insecurity has now entered the forefront of my priorities.

With a background in neuroscience and lifelong interest in gastronomy acting as a merging academic lens, one particular form of food advocacy of interest is helping those who had their palates altered due to a medical diagnosis. COVID-19 strained the human population in such multi-dimensional ways, including an unprecedented number of people experiencing the loss of sense of smell and altered taste perception. This raises many a question from how one can tell if food is rancid, to keeping on weight if not motivated to eat, making wise choices in selecting sometimes less flavorful unprocessed food items, and even maintaining social and cultural connection when disengaged from such a pivotal part of the human experience.

Brain Taste Mechanisms

The human brain contains over 1.1 trillion cells, with millions of neurons and several different neural pathways dedicated to taste and smell. Evolutionarily speaking it was a survival tactic— today it helps define us as a species. Food has become such a multi-faceted experience apart from essential nourishment. It encompasses our daily lives through formulating our emotional well-being and is even pivotal in the formulation of memories.

“Smell is directly related to human emotions; it is the main trigger for human emotions after sight. In fact, it has been reported that 75% of human emotions are created through aroma. The olfactory bulb is part of the brain’s limbic system (seat of emotions, desires, and instincts), and that is why smells can trigger strong emotional reactions. This explains the strong link between smells, emotions, and memories (Girona Ruíz 1).”

Many have experienced the typical cold or flu where food flavors were dulled. This is mainly due to congestion, where aroma molecules are retronasally blocked from chemoreceptors in our nose (Erenstein 1). Frequently coined anosmia, it is a phenomenon where there is a physical blockage contributing to the loss of smell, which comprises 90% of taste or flavor. Soon after the influx of COVID-19 patients reporting such symptoms, scientists were quick to leap to uncover more details.

COVID-19 Statistics & Symptoms

Forty to sixty percent of positive COVID-19 cases reported experiencing a form of smell loss. Sometimes this was even the only symptom experienced, in the absence of any fever or flu symptoms. The scientific community thinks that the number might have been as high as eighty percent (Froum 1). Many extended this sensation to taste loss, losing the ability to distinguish food flavors. The technical terms for these occurrences are as following—

“total or partial loss of smell (anosmia/hyposmia) and taste (ageusia/hypogeusia), distorted perception of smell/taste (parosmia and parageusia), and perception of an odor or a taste without any concurrent stimulus (phantosmia, also known as olfactory hallucination, and phantogeusia, also known as gustatory hallucination) (Ercoli 1).”

For those reporting phantosmia, or olfactory hallucinations, the smell they described was that of a burning fire while parosmiatic patients smelled garbage or rotten food while eating. Parageusia patients described fuel, iron and plastic taste sensations while partaking in meals (Ercoli 3).

These statistics can be particularly troubling because most will agree that an individual battling COVID-19 can most definitely benefit from nutritive foods to help support their immune system as they recover to a more optimal state of health. Already isolated because of their diagnosis, individuals are usually left to navigate this newly twisted maze of sensations in an environment where they might not even have a large range of foods available to them, nor the motivation or physical capability to cook for themselves.

COVID-19 Olfactory Mechanisms

Why does food suddenly smell of burning fuel and decomposing trash, and food taste like metal and plastic? This intense reaction is thought to be the result of a viral attack on the neural olfactory epithelium, specifically supporting cells with receptors connecting to the olfactory nerve (Froum 1).

“When Meunier and his team at Paris-Saclay University in France infected hamsters with the COVID-19 virus, tiny hair-like projections known as cilia on the surfaces of olfactory neurons began to peel back from sustentacular cells. This disruption is a possible explanation for the difficulties with smell that patients experience (Erenstein 2).”

The brain of a COVID-19 patient has trouble interpreting sensory signals of incoming odors originating from the nose because of the sustentacular cell damage the virus has caused. The good news is that the olfactory nerve and olfactory support cells both possess the capabilities to regenerate within a matter of a couple weeks.

“On average, 50% of patients will recover their sense of smell in the first two to three weeks and another 40% in the first eight weeks post infection. (Froum 1)”

Potential Treatments

Health practitioners have been known to prescribe both intranasal and systemic corticosteroids to their patients as a first-line therapy for smell loss but the actual effects are still unclear (Mullol 2). Other studies examine the benefits of using phosphodiesterase inhibitors and intranasal calcium buffers, but overall there is little rigorous study, few known interventions, lack of demonstrated efficacy and safety concerns with this set of medical recommendations (Levy 1).

The silver lining in this smell predicament is that olfactory support cells do regularly regenerate.  Since the loss of smell is typically temporary, practitioners became interested in exploring mechanisms in which patients could be given the chance to retrain their senses.

“Compared to baseline, training patients experienced an increase in their olfactory function, and for thresholds for the odors used in the training process. In contrast, olfactory function was unchanged in patients who did not perform olfactory training. The present results indicate that the structured, short-term exposure to selected odors may increase olfactory sensitivity (Hummel 1).”

In fact, olfactory training is the only intervention that demonstrates effective results. The exact mechanism is unknown, but the thought is that the “repeated stimulation of olfactory neurons by clearly defined odorants increases both the regenerative ability and the neuroplastic potential of this unique system (Levy 1)”. The average amount of time recommended to spend retraining your sense of smell is approximately two to three months.  The chosen scents are strong, yet typically pleasant ones— spices, florals, citrus and botanicals.

“A British company, AbScent, sells kits with rose, lemon, and eucalyptus. Scientists have found that recurring exposure to these strong scents gives the brain time to recalibrate its networks, a feature known as neuroplasticity (Erenstein 3).”

Utilizing Specified Scents for Restoring Intranasal Function

In one clinical study, patients exposed themselves two times per day for a period of twelve weeks to four specified odorant molecules: phenyl ethyl alcohol: rose (flower), eucalyptol: eucalyptus (resonance), citronellal: lemon (fruit), and eugenol: cloves (spicy) (Hummel 1). This technique has been originally developed by otolaryngologists prior to COVID-19 occurrences, and recommends the usage of essential oils (Froum 2).

“There are three types of scents used in environments known as head, heart, and basic. Head scents are generally small, light molecules that give a refreshing and invigorating sensation. These are typically fresh citrus or green notes, including lemon, lime, neroli, bergamot, grapefruit, and cooler herbal notes such as lavender, thyme, and basil. The molecules responsible for heart-like scents tend to be larger and can take anywhere from five minutes to an hour to develop. They can include different ingredients, such as flowers, spices, woods, resins, and grasses. Lastly, the basic-type scent molecules are the largest and heaviest. They are aromas such as woods, resins, oakmoss, vanilla, amber, and musk. (Girona-Ruíz 3)”

Scientists have also cited Alzheimer’s and Parkinson’s diseases, head trauma, and chemotherapy as triggers for anosmia (Erenstein 1). What is particularly interesting about essential oils is that they can tout further benefits that can resonate with other neurological conditions such as dopamine release in depression cases (Fukumoto 1), improvement of cognitive function in individuals with dementia (Agatonovic-Kustrin 2402), and neuroprotective effects in Alzeihmer’s patients (Aboubakr 111).

Discussion & Concluding Thoughts

There is some irony in the fact that we live in a modern age where we are constantly inundated with a plethora of processed foods loaded with excitatory flavor molecules that essentially hijack our neural pathways, while the COVID-19 virus left a good sector of the population in neurological sensory digress. Any coping strategies that can help an afflicted population can certainly make a positive impact in the lives of many. In the case of essential oils, they are not only accessible to most from a monetary standpoint, but the regime is simple enough to follow to be inclusive to most individuals.

Food is a deep source of comfort, human connection and nourishment. As a chef, when seasoning food we advise more acid, sweetness, salt or a drizzle of finishing oil. What do you feed a person who can no longer experience the sensation of taste? COVID-19 left a significant sector of our population isolated, confused and looking for answers. In addition to olfactory retraining with essential oils, it would be interesting to explore if sounds, comfort foods, environmental cues, pigments, and physically touching and assembling food items could also hold olfactory regenerative potential.

It being a worldwide occurrence, the COVID-19 pandemic brought asomnia to the spotlight, with widespread funding made available. The olfactory retraining results have been promising thus far, but more studies need to be conducted to form a more complete picture of which other scents can potentially be used, to confirm if 8 to 12 weeks is the definitive training window and if two times per day for 20 seconds per session is indeed the optimal exposure strategy. It is nevertheless exciting to be able to potentially apply these findings to other neurodegenerative conditions.  Hopefully the whole world will continue to stay involved in studying how to unlock plant potentials to provide relief to neurological conditions affecting millions of individuals.

WORKS CITED:

Aboubakr, Mohamed, et al. "Neuroprotective effects of clove oil in acrylamide induced neurotoxicity in rats." Pak Vet J 39.1 (2019): 111-115.

Agatonovic-Kustrin, Snezana, et al. "Models for skin and brain penetration of major components from essential oils used in aromatherapy for dementia patients." Journal of Biomolecular Structure and Dynamics 38.8 (2020): 2402-2411.

Erenstein, Daniel. "COVID-19 survivors can retrain their smell to enjoy food and wine again.” The Aggie Transcript, 24 Sept. 2021, https://aggietranscript.ucdavis.edu/covid-19-survivors-can-retrain-their-smell-to-enjoy-food-and-wine-again/

Ercoli, Tommaso, et al. "Qualitative smell/taste disorders as sequelae of acute COVID-19."  Neurological Sciences 42.12 (2021): 4921-4926.

Froum, Scott. "Olfactory training and COVID-19-related loss of smell March 8, 2021 Dr. Scott Froum explains how essential oils can help retrain neurons damaged by coronavirus and speed along recovery.”

Fukumoto, Syuichi, et al. "Flavor components of monoterpenes in citrus essential oils enhance the release of monoamines from rat brain slices." Nutritional neuroscience 9.1-2 (2006): 73-80.

Girona-Ruíz, Dámaris, et al. "Aromachology related to foods, scientific lines of evidence: A review." Applied Sciences 11.13 (2021): 6095.

Hummel, Thomas, et al. "Effects of olfactory training in patients with olfactory loss." The Laryngoscope 119.3 (2009): 496-499.

Levy, Joshua M. "Treatment recommendations for persistent smell and taste dysfunction following COVID-19—the coming deluge." JAMA Otolaryngology–Head & Neck Surgery 146.8 (2020): 733-733.

Mullol, Joaquim, et al. "The loss of smell and taste in the COVID-19 outbreak: a tale of many countries." Current allergy and asthma reports 20.10 (2020): 1-5.