Survey results
I recently did an MS-Selfie Q&A newsletter on the impact of having MS on taste and included a survey (please see: Q&A-33 multiple sclerosis and taste; 4-May-20204)
In short, two-thirds of readers were unaware that MS could impact taste. So, this newsletter addressed an unmet need.
Almost two-thirds of respondents stated that they had or may have experienced and alteration in taste that could be MS-related. This figure is much higher than I expected, but not surprising.
The most commonly reported change in taste was reduced (hypogeusia) or altered taste (dysgeusia). However, eight respondents described ageusia or loss of taste. Many respondents also described other changes in their taste, such as heightened or intermittent metallic tastes. Not surprisingly, changes in taste often occur as part of an MS relapse, indicating that MS disease activity can impact taste function. The majority of you who reported MS-related alterations in taste had yet to have them investigated or treated by your MS HCPs. Is this a problem?
Taste and MS
It is well known that MS can lead to changes in taste perception, resulting in a range of symptoms. Taste is a sensory modality not studied in depth in people with multiple sclerosis (pwMS). In a small study (see below), the taste identification scores for sucrose, citric acid, caffeine, and salt were significantly lower in pwMS. In 15-32% of subjects with MS, taste identification scores fell below the 5th percentile of controls for the different substances. These scores were inversely correlated with MRI MS lesion volume. Interestingly, women outperformed men in terms of taste.
A large proportion of pwMS exhibit taste deficits that are associated with MS-related pathology throughout the brain. Altered taste function is yet another hidden symptom of having MS.
Understanding altered taste in MS
Dysgeusia is a persistent, unpleasant taste in the mouth, manifesting as a metallic, bitter, or salty flavour. MS typically causes hypogeusia or diminished ability to taste flavours, reducing the perception of sweet, sour, salty, or bitter tastes as described above. Ageusia is a complete loss of taste perception, which rarely occurs in MS and significantly impacts an individual's ability to enjoy food. I have only seen one patient in my career who had a reversible loss of taste due to a brain stem relapse.
Altered taste sensation has implications for nutritional intake. Changes in taste perception may lead to a decreased appetite, aversion to certain foods, and difficulty enjoying meals. This could lead to poor dietary choices and inadequate nutritional intake. The new GLP1 agonists (e.g. semaglutide (Ozempic/Wegovy) or tirzepatide (Zepbound/Mounjaro)) are thought to modulate taste perception and cause food to taste bland. This is part of their action mode and why they cause weight loss.
The MS lesions that can affect taste are typically located in the areas associated with taste processing. These areas include the brainstem, thalamus, and cerebral cortex, which are involved in taste (gustatory) perception. When lesions form in these regions due to MS, they disrupt the transmission of taste signals and lead to alterations in taste perception.
Please be aware that if you have altered taste, don’t assume it is MS. Altered taste can be caused by a variety of factors, including:
Infections: Respiratory infections, sinus infections, and other illnesses can temporarily affect the taste buds, leading to a distorted taste perception. This was particularly common with SARS-CoV-2 during the COVID-19 pandemic.
Medications: Certain medications, such as antibiotics, antihistamines, and chemotherapy drugs, can cause taste disturbances as a side effect.
Dental issues: Oral conditions like gum disease, dental infections, or injuries to the mouth can impact taste sensation.
Other neurological conditions: Apart from multiple sclerosis, other diseases affecting the nervous system, such as Parkinson's disease or Bell's palsy, can lead to altered taste perception.
Chemical exposure: Certain chemicals or environmental toxins can change taste perception.
Nutritional deficiencies: Deficiencies in certain nutrients, such as zinc, vitamin B12, or folate, can lead to taste abnormalities.
Smoking: Smoking can reduce one's ability to perceive flavours.
Identifying the underlying cause of altered taste is important for determining the appropriate treatment and management strategies. Having MS may increase one's susceptibility to the effects of other diseases and medications that affect taste.
Managing taste disturbances in MS can be challenging, but there are strategies that pwMS can employ to improve their eating experience. If loss or altered taste is due to a relapse, a course of high-dose steroids may help. If reduced or altered taste persists, you can try experimenting with flavours by exploring different seasonings, herbs, and spices, enhancing the taste of foods and making meals more enjoyable. Adapting foods' texture, such as creamy or crunchy elements, can provide a more satisfying eating experience, even if the taste perception is altered. If you can’t get on top of troubling taste symptoms, you may need to see a dietician and/or oral medicine expert. A dietician can help you develop a personalised diet plan to meet your nutritional needs despite taste disturbances.
By understanding these challenges and implementing appropriate coping strategies, individuals with MS should be able to work towards maintaining a balanced diet, which hopefully is enjoyable.
Calorie-sensing
There is more to taste than its perception. The human body has a sophisticated calorie-sensing system for detecting and managing calorie intake. This system helps maintain energy balance and, hence, impacts metabolic health. However, while artificial sweeteners are beneficial in reducing sugar intake, they have raised concerns about their impact on the physiological function of calorie-sensing. Calorie sensing involves multiple physiological mechanisms that enable the body to gauge calorie intake and energy expenditure. This process is vital for maintaining homeostasis and preventing both undernutrition and overnutrition.
Sensory input: The taste buds and gut cells have receptors that respond to the caloric content of food, sending signals to the brain.
Hormonal responses: Hormones such as insulin, leptin, and ghrelin play pivotal roles in hunger regulation and energy storage.
Metabolic adjustments: The body adjusts its metabolic rate based on perceived calorie intake to maintain energy balance.
Artificial sweeteners are widely used as substitutes for sugar, offering sweetness without the calories. Examples include aspartame, sucralose, and saccharine. While artificial sweeteners are advantageous for reducing caloric intake, they challenge the body's natural calorie-sensing mechanisms. Artificial sweeteners provide intense sweetness with little to no calories. This discrepancy can trick the body into expecting energy that isn't delivered, potentially leading to increased appetite and overeating. Several studies have shown that artificial sweeteners can alter gut microbiota, impacting metabolism and energy utilisation. The sweet taste of artificial sweeteners triggers insulin release in anticipation of glucose. However, when artificial sweeteners are consumed regularly, this response can become disjointed, potentially leading to insulin resistance over time.
If you use artificial sweeteners, you must be aware of their impact on your health. There is now overwhelming evidence that artificial sweeteners are associated with cardiovascular disease (see paper 2 below). As vascular disease is linked to worse MS outcomes, will the regular consumption of artificial sweeteners lead to worse MS outcomes?
From an evolutionary medicine perspective, it is best to avoid artificial sweeteners. Why would we hijack a physiological system (calorie-sensing) to try and reduce sugar consumption? Do you agree?
For those of you who are not paying subscribers, I would like to hear if you have noticed problems with taste, either as part of a relapse or as a complication of smouldering or more advanced MS. If you have time, please complete the taste survey.
I would also be interested in your thoughts about artificial sweeteners and MS-related health outcomes. Should we ignore the emerging science or avoid artificial sweeteners to optimise our metabolic health?
Paper 1
Doty et al. Taste dysfunction in multiple sclerosis. J Neurol . 2016 Apr;263(4):677-88.
Empirical studies of taste function in multiple sclerosis (MS) are rare. Moreover, a detailed assessment of whether quantitative measures of taste function correlate with the punctate and patchy myelin-related lesions found throughout the CNS of MS patients has not been made. We administered a 96-trial test of sweet (sucrose), sour (citric acid), bitter (caffeine) and salty (NaCl) taste perception to the left and right anterior (CN VII) and posterior (CN IX) tongue regions of 73 MS patients and 73 matched controls. The number and volume of lesions were assessed using quantitative MRI in 52 brain regions of 63 of the MS patients. Taste identification scores were significantly lower in the MS patients for sucrose (p = 0.0002), citric acid (p = 0.0001), caffeine (p = 0.0372) and NaCl (p = 0.0004) and were present in both anterior and posterior tongue regions. The percent of MS patients with identification scores falling below the 5th percentile of controls was 15.07 % for caffeine, 21.9 % for citric acid, 24.66 % for sucrose, and 31.50 % for NaCl. Such scores were inversely correlated with lesion volumes in the temporal, medial frontal, and superior frontal lobes, and with the number of lesions in the left and right superior frontal lobes, right anterior cingulate gyrus, and left parietal operculum. Regardless of the subject group, women outperformed men on the taste measures. These findings indicate that a sizable number of MS patients exhibit taste deficits that are associated with MS-related lesions throughout the brain.
Paper 2
Objectives: To study the associations between artificial sweeteners from all dietary sources (beverages, but also table top sweeteners, dairy products, etc), overall and by molecule (aspartame, acesulfame potassium, and sucralose), and risk of cardiovascular diseases (overall, coronary heart disease, and cerebrovascular disease).
Design: Population based prospective cohort study (2009-21).
Setting: France, primary prevention research.
Participants: 103 388 participants of the web based NutriNet-Santé cohort (mean age 42.2±14.4, 79.8% female, 904 206 person years). Dietary intakes and consumption of artificial sweeteners were assessed by repeated 24 h dietary records, including brand names of industrial products.
Main outcomes measures: Associations between sweeteners (coded as a continuous variable, log10 transformed) and cardiovascular disease risk, assessed by multivariable adjusted Cox hazard models.
Results: Total artificial sweetener intake was associated with increased risk of cardiovascular diseases (1502 events, hazard ratio 1.09, 95% confidence interval 1.01 to 1.18, P=0.03); absolute incidence rate in higher consumers (above the sex specific median) and non-consumers was 346 and 314 per 100 000 person years, respectively. Artificial sweeteners were more particularly associated with cerebrovascular disease risk (777 events, 1.18, 1.06 to 1.31, P=0.002; incidence rates 195 and 150 per 100 000 person years in higher and non-consumers, respectively). Aspartame intake was associated with increased risk of cerebrovascular events (1.17, 1.03 to 1.33, P=0.02; incidence rates 186 and 151 per 100 000 person years in higher and non-consumers, respectively), and acesulfame potassium and sucralose were associated with increased coronary heart disease risk (730 events; acesulfame potassium: 1.40, 1.06 to 1.84, P=0.02; incidence rates 167 and 164; sucralose: 1.31, 1.00 to 1.71, P=0.05; incidence rates 271 and 161).
Conclusions: The findings from this large scale prospective cohort study suggest a potential direct association between higher artificial sweetener consumption (especially aspartame, acesulfame potassium, and sucralose) and increased cardiovascular disease risk. Artificial sweeteners are present in thousands of food and beverage brands worldwide, however they remain a controversial topic and are currently being re-evaluated by the European Food Safety Authority, the World Health Organization, and other health agencies.
Trial registration: ClinicalTrials.gov NCT03335644.
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General Disclaimer
Please note that the opinions expressed here are those of Professor Giovannoni and do not necessarily reflect the positions of Queen Mary University of London or Barts Health NHS Trust. The advice is intended as general and should not be interpreted as personal clinical advice. If you have problems, please tell your healthcare professional, who will be able to help you.
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