A matter of taste: alteration in patients with cancer

Malnutrition is a common feature in cancer patients and is associated with more complications, poorer tolerance of treatment and increased morbidity and mortality. Maintaining nutritional status is recognised as a major part of cancer care. European guidelines in clinical nutrition in cancer recommend screening to detect nutritional disturbances as early as possible, beginning with cancer diagnosis (Muscaritoli et al, 2021).

Taste alteration and changed taste perception is also common in patients with cancer. This can be as a result of the cancer itself, its type and stage, as well as treatment regimens of chemotherapy and radiotherapy. It is reported to be as high as 70% in cancer patients receiving chemotherapy, with significant associations between taste alterations and fatigue, appetite and quality of life (Zabernigg et al, 2010). Alterations in taste and smell functions are not confined to patients on active treatment, with common complaints in advanced cancer being persistent bad taste in the mouth, distorted taste and heightened sensitivity to smells. In a study by Hutton et al (2007) at a regional cancer centre, up to 86% of patients with advanced cancer reported some degree of perception abnormality to taste and smell. Taste alteration is a nutritional impact symptom likely to adversely affect dietary intake and compromise nutritional status, adding to the risk factors for developing malnutrition.

Altered taste perception can not only cause physical problems, but can also cause emotional distress, result in reduced appreciation of food, and have a negative impact on social functioning. Despite the high prevalence, there is a lack of evidence-based strategies and guidelines to support a standard definition, identification and management of taste alterations. Patient support material and literature on the topic often recommends various strategies, including increased use of herbs and spices, using non-metal cutlery and adding sharp and tart foods to refresh the palate. There is a lack of evidence for the efficacy of these interventions.

Taste and its alteration in cancer

Taste alterations can describe a wide range of experiences, which can vary greatly between individuals. Cancer patients can report a change in perception and sensitivity, for example, noting foods appearing to be less salty or less sweet than usual (hyposensitivity), or they may report heightened sensitivity (hypersensitivity), for example, to a bitter taste, which can become almost unbearable. Some will report a continuous, long-term sensation of a metallic or chemical taste in the mouth and this can occur very early in a cancer patient's journey. The PreMiO study (Muscaritoli et al, 2017), an observational study assessing nutritional status and related factors at the patients' first oncological appointment, before any treatment, highlighted that as many as 41% of newly presenting patients had a loss of appetite. Among the reasons for appetite loss were:

• Taste changes in 41%
• Meat aversion in around 30%
• Smell disturbances in around 20%.

Routine assessment of patients' needs, including nutritional impact symptoms such as reduced appetite and taste alterations, should be encouraged as early as possible after diagnosis.

There are five taste sensations, all of which can be affected:

• Sweet
• Sour
• Bitter
• Salty
• Umami.

Taste is a sense that develops through the interaction of dissolved molecules from food—such as sodium ions (Na+) reflecting saltiness, or sourness from free hydrogen ions (H+) – with taste receptor cells on taste buds located on the tongue, soft palate and oropharyngeal regions. Taste is only one aspect of the overall sense of flavour, which also takes account of smell, touch, temperature, texture and oral irritation. Taste and smell are also very closely linked; a change to a person's sense of smell can affect how things taste.

Effects of chemotherapy and radiotherapy

Chemotherapy is thought to act on the most rapidly dividing cells, including the taste and smell receptor cells, which have an approximate life span of 10-20 days, so it is likely that the cytotoxic effect has a damaging impact.

Radiotherapy to head and neck and upper gastrointestinal cancers can alter taste perception due to the direct damage to the taste cells and buds, the oral cavity and the microvilli lining the nasal cavity in the radiotherapy field. It can also cause damage to the salivary glands affecting the composition, quality and quantity of saliva production.

Tables 1 and 2 outline the potential effects of these therapies on taste.

Dry mouth (xerostomia)

Saliva acts as a solvent; it dilutes and disseminates these molecules to the taste receptors that facilitate tasting. People who have a dry mouth (xerostomia) will often report distorted or diminished taste. Each taste bud contains up to a hundred taste cells and several specialist taste cells, or gustatory receptor cells, for the transduction of taste stimuli. Once the receptor cells are chemically activated they release neurotransmitters, which activate the nerve fibres in the glossopharyngeal nerves to the taste-processing region of the brain in the cerebral cortex and the taste is experienced. The trigeminal nerve is also involved in tasting through the perception of touch, pressure, temperature and pain (eg spicy foods).

Xerostomia is a condition in which the salivary glands in the mouth do not make enough saliva to keep the mouth wet. This lack of saliva can not only affect taste perception but also adversely affect the sensation of food texture and texture perception in the palate and increase the difficulty in mastication. This can make the experience of eating more uncomfortable and unpleasant. Patients often report food ‘tasting like cardboard’, which is likely describing not only the perceived taste but also the perceived texture change.

Although commonly recognised in radiotherapy, xerostomia can also be present in patients receiving chemotherapy and is associated with taste change. Silva et al (2021) measured symptoms of xerostomia and taste using the Chemotherapy-Induced Taste Alteration Scale (CiTAS) in a group of solid tumour patients receiving chemotherapy. The CiTAS scores were significantly higher in those patients who were reported as having xerostomia compared with those who did not, indicating that they had an increased intensity of taste alterations.

Dry mouth can also be caused by some medicines including antidepressants, diuretics, pain medications and antiemetics (to treat nausea and vomiting), many of which will be commonly used in cancer management. It would therefore be logical when discussing taste perception to assess for dry mouth and implement some of the strategies known to alleviate it, for example, to encourage soft moist foods, or moisten dry foods with nourishing sauces.

The pleasure of eating (food hedonics)

Hedonics refers to the psychological determination of the extent to which a life experience gives us pleasure. When evaluating eating experiences, food hedonics could be referred to as food liking, and liking as the experience or anticipation of pleasure from the oro-sensory stimulation of eating a food. Food hedonics is likely to be influenced by many of the properties related to taste alteration, including smell, mouthfeel and temperature. A reduction in joy or pleasure from food and food aversion is likely to have an effect not only on oral intake and appetite but also on social eating habits and social functioning.

The hedonic/liking experience is also thought to change during chemotherapy, according to Boltong and Keast (2012). This systematic review highlighted changes in food liking and associated food aversions and a general trend of decreased liking of food as chemotherapy begins. The review showed those foods and drinks most commonly reported as producing reduced liking were caffeinated foods and drinks, red meat and citrus fruits and juices. It may be useful to prepare patients with this information and possible alternatives, for example to red meat, to continue to ensure an adequate protein intake. It could also have implications for current dietary strategies encouraging the use of sharp/tart foods and flavours as palate cleansers.

TASTE trial

The TASTE trial, which was carried out in cancer patients undergoing chemotherapy (Von Grundherr et al, 2019), may lead to more clinical training strategies. This trial used intensive nutritional counselling alongside taste and smell training to improve taste disorders. It involved a 15-minute taste and smell training session where blindfolded patients tasted specific drinks (eg different fruit juices and teas) and foods (eg pretzel sticks) and smelled scent pencils (lemon and cloves). Patients were encouraged to conduct home-based smell and taste training and were also taught how to maintain adequate oral hygiene and encouraged to drink at least 1.5-2 litres of fluid a day.

The result of these interventions after 12 weeks was that, clinically, patients improved their taste by at least 2 taste strip points from baseline. There was a significant improvement in all analysed taste categories—sweet, sour, bitter and salty—although it was noted that salty had the lowest value of all the tastes both at baseline and after the intervention. The authors concluded that intensive nutrition counselling and taste and smell training may improve taste perception of patients undergoing chemotherapy and may shape how to manage chemosensory problems in the future. A confirmatory randomised trial is planned.

Taste perception in advanced cancer

Research in patients with advanced cancer has shown significant association between the increased level of chemosensory symptoms and energy intake (Hutton et al, 2007). Patients completed a 3-day food diary alongside a questionnaire on self-perceived taste and smell abnormalities, which were scored to give a chemosensory complaint score. Patients were grouped by total chemosensory complaint score into four groups: absent, mild, moderate and severe. There was a difference in intake of 900-1100 kcals/day between patients who had severe abnormalities versus those with none.

Food enjoyment and quality of life was also rated lower in the severe group; unsurprisingly this was linked to increased weight loss and reduced time to death. An additional finding in this study, which is consistent with other articles, is the increased perception of bitter or sour taste. Management strategies that incorporate advice on taste changes may be useful in order to assist patients in balancing or neutralising these tastes.

Patients' food preferences

A lot of the patient information and literature available comes from patients' personal experiences and what patients have told health professionals. For example, many patients say they avoid meat because it tastes bitter. It is likely that the information has been supplemented by healthy individuals' experiences of what gives food more flavour, for example, cooking with more herbs and spices. However, it may be useful to apply the learning from observed patient research:

A large study undertaken with 7 cancer centres in the USA including 1199 cancer outpatients receiving treatment (Coa et al, 2015) highlighted that 67% of patients, with a range of tumour sites including breast, lung, gastrointestinal and haematological cancers, reported at least one taste or smell sensitivity. In the patients who had lost weight in this study there was an increased sensitivity to metallic and salty tastes, reduced sensitivity to sour and sweet tastes, and an increased sensitivity to cooking smells.

What was also interesting in this study, and may be helpful when developing patient information materials, was the list of foods that patients showed preferences and aversions for (Table 3). The results highlighted that these taste alterations are individual and also interlink with other nutritional impact symptoms requiring holistic assessment. There were variations with subgroups, for example, gastrointestinal cancer patients were more likely to report gastrointestinal symptoms, including diarrhoea. When looking at their food aversions they were more likely to avoid spicy foods, fruit and vegetables and high-fibre foods, which are thought to be more likely to exacerbate diarrhoea.

A more recent small pilot study, carried out in South Korea, investigated changes in taste threshold and dish preferences of breast cancer patients compared with healthy controls and found that sensitivities to sweet, salty and sour, but not bitter, taste differed between the cancer patients and controls and the sensitivity to sweet increased during treatment. They also showed a preference for mild tastes and soft texture dishes including porridge, fish cakes, soft noodles, boiled potatoes, yogurt and soup, whereas dishes with strong flavours and sweet or greasy dishes were less preferred (Kim et al, 2020).

With the lack of evidence in supporting the management of taste alterations, it may be useful to consider food preferences such as these, and the other common themes identified in the research, to help provide practical and patient sensitive information about recipes, meal and snack suggestions and implementation techniques supporting patients to meet their nutritional requirements.

Nutritional guidelines in cancer

Maintaining nutritional status plays a major part in cancer care. Patients who are malnourished or at risk of malnutrition should be supported to increase their oral intake through dietary advice, nutrition counselling and the treatment of nutrition impact symptoms. According to European guidelines, cancer patients are recommended to have 25-30 kcals per kilogram of body weight per day and their protein intake should be above 1 g of protein per kilogram of body weight per day and if possible up to 1.5 g/kg/day (Muscaritoli et al, 2021).

In a study by Turcott et al (2020), taste alterations were reported in 35% of chemotherapy-naïve lung cancer patients, those patients with dysgeusia had a lower consumption of protein, iron and sodium.

Compromised protein status could be a nutritional issue particularly given that one of the foods most commonly avoided is meat, because it is perceived as bitter. Patients may need to be proactively guided to alternative protein sources to meet requirements and support anabolism, which could include non-meat and plant-based varieties such as fish, eggs, dairy products, Quorn or other meat substitutes, tofu, beans and pulses.

A lower calorie intake has been associated with a reduced taste function in breast cancer patients into their third cycle of treatment (Boltong et al, 2014). This was further highlighted in a mixed cancer population, where cancer patients who had a decreased calorie, protein and zinc intake had a higher sweet detection threshold and a higher bitter recognition threshold, with a number of patients not meeting their energy requirements (Sanchez-Lara et al, 2010). It is important to be aware of the potential for decreased intake and potential decline in nutritional status and to ensure management strategies are appropriate.

Taste alterations and oral nutritional supplements

If nutrition counselling and other tailored management strategies to improve oral intake are not sufficient to meet protein and energy needs, oral nutritional supplements (ONS) are commonly used to help bridge the nutrient deficit (Muscaritoli et al, 2021). Although there are a variety of formats they generally contain protein, energy, vitamins and minerals. They are intended to be an additional source of nutrients and not a replacement for food. The following should be considered:

• The effectiveness of ONS will depend on patient tolerance and compliance
• The presence of taste alterations is likely to affect tolerance
• It is all the more important to offer patients a choice of flavours and texture preferences. ONS come in a range of styles including milk, juice, yogurt, dessert and savoury soup style and a variety of formats including powder, liquid and concentrated small volumes
• Patients should be assessed by a dietitian to support them with their individual nutritional requirements, which should also take account of their perceived taste and mouthfeel disturbances. It is helpful to offer sample packs to assess tolerance and acceptability and reduce taste fatigue (Ravasco, 2005).

De Haan et al (2021) recently published work that highlights the need for more sensory design of ONS to better address the sensory needs of patients with cancer and meet the likings of as many patients as possible. The study used five prototype ONS flavours: a neutral flavour, two ‘hot’ flavours (hot tropical ginger and hot mango with an additional warming sensation in the form of added capsicum derivatives) and two ‘cool’ flavours (cool red fruits and cool lemon with a cooling sensation in the form of menthol derivatives) in an attempt to identify liked flavours and stimulate the trigeminal sensation. Sixty percent of the study group of mixed cancer patients reported taste alterations, of which a chemical or metallic taste were common. For all of the patients three flavours were rated highly: the neutral, the cool red fruits and the hot tropical ginger, particularly in patients with taste alteration. These three flavour varieties are available on prescription in the UK.

Patients with taste alteration also showed a larger variation in their overall liking scale across flavours compared with patients without taste alteration. The results highlight the need for patients with cancer to be involved in the ongoing development of new flavour options.

Supporting taste and smell alterations: practical points

Taking into account the discussion above, the following seems a sensible approach to help manage taste alterations in the absence of more evidence-based guidance:

• Screen for taste alterations, desire for food, eating habits and other associated nutritional impact symptoms
• Prepare patients for the potential occurrence of problems related to taste, smell and food hedonics and that these can vary throughout the cancer journey
• Ensure good mouth care to maintain oral hygiene
• Ensure adequate fluid intake, substituting the bitter and citrus varieties for other fruit or herbal tea (eg peppermint), milk, fruit juices such as apple, mango and pineapple or flavoured squashes
• Check for dry mouth and where present encourage moist nourishing foods such as pasta/noodles in sauce, enriched soups or risottos
• Encourage alternative protein sources where meat is unappetising such as cheese, dairy foods, nuts, eggs, beans and pulses, tofu and Quorn
• Where there is increased sensitivity to smell, advise patients to try to minimise exposure to odour molecules by avoiding cooking smells, using the extractor fan, putting lids on pots, or asking family or friends to prepare nourishing meals. Try nourishing cold or room-temperature foods such as quiche, cold tortilla/Spanish omelette, cottage cheese, pasta salads, or fruit compote and yogurt
• Herbs, spices, increased seasoning, smoked or pickled products may be useful for some individuals, but others prefer more bland, mild options—encourage nourishing options such as milky porridge, cheesy mashed potatoes, creamed chicken in white sauce with rice
• Where ONS are required to supplement intake, ensure patients have the opportunity to sample different styles and flavours and that prescriptions are issued clearly detailing which product and flavour is required, to help support patients' tolerance.

The Malnutrition Pathway website has available a free online resource for professionals including patient factsheets that give advice on dealing with common symptoms and issues interfering with the ability to eat and drink (www.malnutritionpathway.co.uk/cancer).

Conclusion

Taste change is very individual and subjective and in the absence of more evidence-based management strategies patients should be given a range of possible strategies tailored to their individual needs and meeting their nutritional requirements. The provision of timely and appropriate nutritional care is often delayed and in some cases overlooked, adding diet-related anxiety to anxieties that already exist for patients and their families. Individualised nutritional interventions may not only help to improve nutritional status but also have a major effect on the patient's quality of life and overall experience.

More research is required to inform evidence-based nutritional interventions and guidelines, and studies need to consider whether improving the perception of taste and smells in affected patients can improve their intake of food, nutritional status and quality of life.

KEY POINTS

• Taste alterations are common in cancer patients and can be present at various times during the patient pathway, from diagnosis' through treatment, in rehabilitation and in advanced cancer
• A dry mouth can be associated with taste changes and can make chewing and swallowing uncomfortable – good oral hygiene and an adequate fluid intake should form part of any support strategy
• Lower protein, energy and micronutrient intakes have been associated with taste alterations in cancer patients with overall potential to affect nutritional status and outcome
• Nutritional screening, to include taste alteration, should be undertaken as soon as possible after diagnosis and should be repeated at key points in the cancer pathway
• Oral nutritional supplements may be used to bridge nutrient gaps – it is vital to take account of perceived taste changes and mouthfeel disturbances when helping select flavours and styles and also vital that patient tolerance and compliance are regularly assessed

CPD reflective questions

• Reflect on how the information here might be different on managing taste alteration compared with the information you would have previously given a patient
• At what point would you discuss with a patient any issues they have with taste alteration?
• Could screening/assessing for taste alteration form part of an existing tool or checklist where you work?