Investigating oral somatosensory perception and oral symptoms of head and neck cancer patients: insights on eating behaviour

Altered eating, or “losing the ability to eat well”, is a problem among cancer patients, including and especially among head and neck cancer (HNC) patients due to the cancer location being in the food ingestion site [1‐3]. Several side effects were reported prior to, during, and following cancer treatments that interfere with their eating ability. These oral symptoms include dry mouth, chewing/swallowing difficulty, and mucositis [4, 5]. The symptom of dry mouth is reported by up to 90% of HNC patients following radiotherapy, which affects their ability to eat since a reduction in saliva alters the formation of the food bolus and makes swallowing difficult [5, 6]. Mucositis, experienced by 80–90% of HNC patients, induces pain and oral discomfort, which also affects their ability to eat [5, 7]. These oral symptoms lead to an alteration in eating habits that reduce food intake and may contribute to a decline in nutritional status [5, 8]. For instance, 51–74% of HNC patients were malnourished [2, 3]. It also adds a psychological burden as patients lose pleasure from eating and the social interactions surrounding mealtimes [9]. Consequently, this leads to a lowered quality of life [10].

Another aspect that contributed to the altered eating experience was the sensory aspect. Altered sensory perception plays a crucial role in cancer patients’ eating behaviour. Eating behaviour is a broad and complex term encompassing aspects of eating that can influence individuals’ nutritional choices. This includes food choices (preferences and avoidance), food intake, and eating experience [11]. It was shown that sensory alteration was correlated to lower energy intake and higher weight loss, contributing to declined nutritional status and quality of life of advanced HNC patients and patients with gastrointestinal stromal tumours [10, 12].

Several studies have investigated sensory alterations among HNC patients, focusing on alterations in smell and taste perception, with the prevalence ranging from 30 to 80% [13, 14]. However, sensory perception is not only limited to taste and smell but also somatosensation, which few studies have investigated [1, 15, 16]. Somatosensation comprises perception towards texture, temperature, and chemesthetic sensations (e.g. spiciness of chilli and cooling sensation of peppermint) processed by the trigeminal system [17]. In addition, overall food perception is highly dependent on the oral condition, such as salivary function and oral health status. For instance, it was shown that saliva influences the perception of food texture [18].

HNC patients reported oral complaints such as sensitivity to texture, sensitivity to spices, dry mouth, mucositis, and difficulty in chewing or swallowing [1, 15]. These oral complaints are related to somatosensory aspects and oral symptoms. HNC patients also reported that these changes have led to adjustments in their diets, such as adding sauce/gravy to add extra moisture to the food, blending the food, and avoiding certain foods with difficult textures (e.g. dry bread, red meat, hard vegetables) [16]. To better understand their eating experience, it is necessary to assess not only their taste and smell perception but also their somatosensory perception and oral symptoms. In contrast to the objective evaluation of somatosensation and salivary measures detailed in the previous part of our study [19], the present investigation delved into the self-reported sensory perception and oral symptoms of HNC patients, and their association with eating behaviour. It was hypothesised that sensory alterations among HNC consist not only of taste and smell alterations but also somatosensory alterations along with oral symptoms, altogether related to modified food preferences and eating behaviour.

More than half of the HNC patients in this study reported experiencing sensory alterations, which is in agreement with the prevalence of self-reported sensory alteration ranging between 12 and 84% among various cancer patients [11]. Among these HNC patients, changes in taste and somatosensory perception (texture, temperature, and chemesthesis) were reported more frequently than changes in smell perception (Fig. 1), which is consistent with earlier observations [26]. A study showed that changes in smell perception tend to be gradual and unnoticed compared to taste perception [27].

The study highlights the relationship between sensory alteration, sensory-related food preference, and eating behaviour. Upon categorising the patients into two distinct profiles, the alteration group demonstrated a higher proportion of patients with a reduced preference for all somatosensory sub-modalities as well as towards bitter and sour tastes. These findings suggest that changes in sensory perception are linked with sensory-related food preferences. Similar observations have been reported in previous studies [20, 28]. Among patients receiving anti-tumour therapy, significant differences in product preferences of various oral nutritional supplements (ONS) were observed in the patient group with altered perception but not in the unaltered perception group [21]. Among testicular cancer patients, taste and smell sensitivity was associated with liking of ONS [28]. Further, previous studies showed that sensory alteration was related to reduced appetite, food appreciation, and food selection or intake [29‐31].

The presence of sensory alteration was also reflected in items concerning eating behaviour. A higher proportion of patients with sensory alteration agreed to the negatively connotated statements compared to the no alteration group. The HNC patients in the alteration group experienced more eating difficulties such as eating in smaller portions, having food aversion, and having difficulty eating certain foods. This may consequently lead to lower food intake, as it was shown that sensory alterations were correlated with a negative impact on nutritional status [5, 10].

The present study demonstrated that HNC patients experienced several oral symptoms. The oral symptoms frequently experienced by patients were dry mouth, sticky saliva, difficulty chewing, difficulty swallowing, food stuck in the mouth, and food stuck in the throat. These symptoms seem to be mediated by the lack of salivation, as observed in our previous publication [19]. The perception of dry mouth and sticky saliva were experienced by 80% and 60% of patients, respectively. The prevalence of dry mouth and thick saliva among HNC patients who have completed radiotherapy in previous studies was approximately 90% [5, 32]. The prevalence was higher in previous studies as they were assessed at the end of their radiotherapy, whereas in this study patients were included 4 months to 5 years after the end of their radiotherapy. Xerostomia, defined as the subjective perception of dry mouth and/or sticky saliva due to reduced salivary flow, has been widely reported to be one of the most common side effects in this subpopulation of cancer [33].

Difficulty in swallowing and chewing were experienced by 67% and 57% of patients, respectively. Saliva is responsible for bolus formation during mastication, in “wetting and coating, hydration, and granulation” [34]. Lack of saliva will cause the food to be more compact and cohesive, making it more difficult to chew [35, 36]. In addition to salivation, difficulty in chewing may be influenced by age, jaw muscle activity, and use of dentures [35]. Following mastication, the bolus needs to be optimally moistened before it can be swallowed; hence, sufficient saliva is also necessary to facilitate swallowing [34, 37]. Previous studies have shown that difficulty in food processing is common among HNC patients post-radiotherapy, ranging from 88 to 90% for swallowing difficulty and 40 to 63% for chewing difficulty [5, 32, 38]. These altogether may lead to fear of eating due to the risk of choking [39].

Food sticking in the throat and mouth was experienced by 57% and 53% of patients, respectively. These, too, can be associated with salivary function. The hydrating and lubricating properties of saliva facilitate oral clearance [40]; therefore, the lack of it causes food to get stuck in the mouth and/or throat. The other oral symptoms that the HNC patients in this study frequently experienced were dental problems, sensitive teeth/gum, pain in the throat, and pain/problems with teeth. These symptoms can be related to salivary function, as saliva protects teeth and oro-oesophageal mucosa [40]. It was shown that pain surrounding the oral cavity was one of the symptoms reported by HNC patients associated with cancer treatments such as radiotherapy and chemotherapy [4, 5]. Further, it was suggested that severe oral symptoms may influence patients’ physical functioning, quality of life, and nutritional status [41].

The correlation between oral symptoms and sensory perception was observed. Oral symptoms, such as difficulty in chewing and swallowing, food getting stuck in the mouth, and pain in the oral cavity, were positively correlated with texture and temperature perception. It implies that patients affected by these oral symptoms exhibit increased awareness or caution when selecting foods, aiming to avoid food textures and temperatures that may cause pain or discomfort upon consumption.

In addition to the aforementioned oral symptoms, dry mouth, and oral inflammation were also correlated to the preference for sourness, spiciness, astringency, carbonation, and alcohol. Saliva serves multiple functions, including sensory perception, food oral processing, and digestion [39]; hence, impairment in salivary production may influence their eating experience and food intake. A previous study demonstrated that salivary quantity was related to the perception of oral comfort, depending on the food products. The food needs enough moisture, or compensated with some fat, to be easily processed and ingested [42]. The amount and composition of saliva influence the perception of food texture [43]. Further, the interaction between salivary protein and polyphenols influenced the perception of astringency [44, 45], whereas spiciness will become an irritating sensation with the presence of oral pain and inflammation.

Finally, the correlations between oral symptoms and eating behaviour also demonstrated that patients with more oral symptoms have more difficulty in eating situations. Notably, patients with more oral symptoms were correlated with having less appetite, eating smaller portions, not feeling at ease when eating out, not liking food before tasting, developing food aversion, and making certain foods unpleasant or difficult to eat. Consequently, it was reported in previous studies that patients with more serious oral symptoms had reduced intake and higher weight loss [4, 5]. Therefore, both sensory alterations and oral symptoms may affect patients’ eating experience, contributing to adverse nutritional and health outcomes.

Prior research has identified discrepancies between objective and self-reported measurements of sensory alterations. In particular, self-reported taste alterations tend to be overestimated, whereas subjective smell alterations tend to be underestimated [13, 14]. Relying solely on objective measurements may underestimate the complex and subjective nature of the eating experience. Patients reported altered somatosensory perception, consistent with altered somatosensory measures observed previously [19]. However, it is important to note that the results obtained from these two measurements cannot be directly compared. The objective measurements captured the current situation, while the self-reported sensory perception was captured in a retrospective manner (i.e. “in comparison to before the cancer treatment, my sensitivity has”).

This study has limitations, including its small sample size and cross-sectional design; therefore, it cannot infer causation. As the sensory perception was based on retrospective response, it would have higher validity if conducted in a longitudinal design comparing the perception before the cancer treatments and a few time points following the treatments. Moreover, data on oral health status (e.g. number of teeth, occlusal functional units) and use of palliative care (e.g. artificial saliva), which may influence food perception and eating behaviour, was not assessed. However, the study still indicates that patients perceived somatosensory alteration, together with adverse oral symptoms, as being related to greater eating difficulties, which can potentially lead to deteriorated nutritional outcomes.

Eating is a fundamental act that not only fulfills physiological needs but also carries psychological value. The primary findings of the present study showed that more than half of the HNC patients perceived sensory alterations, including their somatosensory perception. These alterations were associated with different aspects of eating including sensory-related food preference and eating behaviour. In addition, common oral symptoms related to salivary dysfunction were reported by patients, which also influenced their eating experience. Patients with perceived sensory alterations and oral symptoms were more likely to face challenges in eating. In order to develop holistic nutritional interventions that enhance patients’ eating experience, it is necessary to consider these two aspects.