Appetite 83 (2014) 236–241

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Research report

Taste perception in kidney disease and relationship to dietary sodium intake ☆ Emma J. McMahon a,b,*, Katrina L. Campbell b, Judith D. Bauer a a b

Centre for Dietetics Research, School of Human Movement Studies, University of Queensland, St Lucia, Qld. 4067, Australia Nutrition and Dietetics Department, Princess Alexandra Hospital, 199 Ipswich Road, Woolloongabba, Qld. 4102, Australia

A R T I C L E

I N F O

Article history: Received 4 February 2014 Received in revised form 7 July 2014 Accepted 10 August 2014 Available online 2 September 2014 Keywords: Taste Sensory assessment Renal disease Dietary sodium Salt intake

A B S T R A C T

Taste abnormalities are prevalent in Chronic Kidney Disease (CKD) potentially affecting food palatability and intake, and nutrition status. The TASTE CKD study aimed to assess taste and explore the relationship of dietary sodium intake with taste disturbance in CKD subjects. This was a cross-sectional study of 91 adult stage 3–5 CKD participants (78% male) aged 65.9 ± 13.5 years with mean estimated glomerular filtration rate of 33.1 ± 12.7 ml/min/1.73 m2, and 30 controls (47% male) aged 55.2 ± 7.4 years without kidney dysfunction. Taste assessment was performed in both groups, presenting five basic tastes (sweet, sour, salty, umami and bitter) in blinded 2 ml solution which the participants tasted, identified (identification) and rated perceived strength (intensity) on a 10 cm visual analogue scale. Sodium intake was measured in the CKD group using validated food frequency questionnaire to determine high or low sodium intake (cut-off 100 mmol sodium/day). Differences between groups (CKD vs controls; high vs low sodium intake) were analysed using chi-square for identification and t-test for intensity. Multivariate analysis was used to adjust for age and gender differences between CKD and controls. The control group identified mean 3.9 ± 1.0 tastants correctly compared with 3.0 ± 1.2 for CKD group (p < 0.001), which remained significant after adjustment for age and gender. After adjustment for age and gender, sour identification and intensity and salty and umami intensity were impaired in CKD compared with controls. Participants with low sodium intake were more likely to correctly identify salty and umami, and rated intensity of umami and bitter significantly higher than those with high sodium intake. These findings add to the body of evidence suggesting that taste changes occur with CKD, independent of age and gender differences, with specific impairment in sour, umami and salty tastes. Our finding that sodium intake is related to umami and bitter disturbance as well as salty taste warrants further investigation. © 2014 Published by Elsevier Ltd.

Introduction Taste is one component of flavour, an important determinant of the overall eating and drinking experience (Boltong & Campbell, 2013). Previous research has indicated that taste disturbance is common in chronic kidney disease (CKD) patients (Fornari & Avram, 1978; Manley, Haryono, & Keast, 2012; Middleton & Allman-Farinelli,

Abbreviations: BMI, body mass index; CKD, chronic kidney disease; eGFR, estimated glomerular filtration rate. ☆ Acknowledgements: The authors acknowledge the Princess Alexandra Hospital Renal Outpatient Department for providing organisational support, the study nurse, Rachael Hale; Prof Russell Keast and Dr Anna Boltong for consultation on sensory assessment; and Prof Carmel Hawley, Assoc Prof Nicole Isbel (study design/ nephrology), Prof Michael Stowasser (study design) and Prof David Johnson (study design/nephrology) for study design consultation. * Corresponding author. E-mail address: [email protected] (E.J. McMahon). http://dx.doi.org/10.1016/j.appet.2014.08.036 0195-6663/© 2014 Published by Elsevier Ltd.

1999; van der Eijk & Allman Farinelli, 1997), with evidence for taste disturbance in five of the basic taste qualities when compared with controls (Kusaba et al., 2009; Middleton & Allman-Farinelli, 1999; van der Eijk & Allman Farinelli, 1997); however, most of these data have come from studies in dialysed patients, with limited studies including those in the earlier stages in CKD. In addition, most evidence thus far has been conducted in studies with small sample sizes, likely due to the time-consuming nature of comprehensively assessing taste (Boltong & Campbell, 2013). Several factors are thought to influence taste in CKD, including the uraemic state, medication usage, salivary changes and differences in dietary intake and nutrition status, including zinc deficiency (van der Eijk & Allman Farinelli, 1997). Taste function has previously been shown to vary with changes in taste-active salivary solutes (Manley et al., 2012). It is thought that increased sodium intake may increase salivary sodium in CKD patients, increasing the salt taste threshold (Manley et al., 2012). Sodium restriction has been shown previously to improve salt taste sensitivity (Kusaba et al., 2009); however, this also has been explored in a small sample size only,

E.J. McMahon et al./Appetite 83 (2014) 236–241

and it is unknown whether dietary sodium is linked to other four taste senses; sweet, bitter, sour and umami. Evidence for the prevalence and nature of taste dysfunction in CKD patients can be used to inform further intervention studies to improve taste function in CKD patients; however, existing data on taste function in CKD to date are limited to studies of small size and mainly in the later stages of CKD. Further, the link between dietary intake and taste dysfunction in CKD has not been explored to date. The TASTE CKD study was designed to overcome these limitations by assessing a large sample of CKD patients, focusing on pre-end stage CKD population where data are sparse, and by exploring the relationship between dietary sodium intake and taste dysfunction. The aims of the present study were to assess the taste function in a large convenience sample of non-dialysed CKD patients, and to explore the relationship between sodium intake and taste disturbance in this population. It is hypothesised that: 1) CKD will be associated with a higher degree of taste disturbances (by incorrect identification of taste stimuli and reduced taste sensitivity as assessed by perceived intensity) compared with healthy controls and 2) high dietary intake of sodium will be associated with impaired salt taste in non-dialysed CKD patients. Material and methods Participants The target population for the study was CKD patients (estimated glomerular filtration rate; eGFR 10–59 ml/min/1.73 m2) attending a single outpatient nephrology clinic from October 2012 to January 2013. Exclusion criteria were those receiving renal replacement therapy (dialysis or transplant), unable to speak and understand English or unable to complete taste testing due to level of mental cognition or comprehension (identified via medical records). Control subjects without kidney dysfunction were recruited, aiming for a similar age and gender distribution. This group was comprised of healthy volunteers as well as participants with hypertension (but with an eGFR > 60 ml/min/1.73 m2) from a separate study. Where possible, eGFR was collected from medical records to verify that the inclusion criteria of eGFR > 60 ml/min/1.73 m2 was met. Where eGFR was not available, medical history was checked, and eGFR was measured only for participants with risk of CKD (e.g. previous history of hypertension of diabetes). Study protocol was conducted in accordance with the ethical standards of the responsible institutional and regional committee on human experimentation or in accordance with the Helsinki Declaration of 1975, as revised in 1983. All participants gave fully informed consent before participation in the study. Measurement of outcomes Assessment of the five primary tastes (sweet, sour, bitter, salty and umami/savoury) was performed using well-established methodology in accordance with the International Organization for Standardization (ISO) method of investigating sensitivity of taste (International Organization for Standardization, 1991). Solutions representing the five basic taste qualities were prepared using standardised methods in a laboratory: sweet (300 mmol/l sucrose), salty (200 mmol/l sodium chloride), sour (5 mmol/l citric acid), bitter (10 mmol/l caffeine), and umami (200 mmol/l sodium glutamate). Participants were presented with a 2 ml sample of each solution in a random order and were asked to hold the solution in the mouth for 10 seconds before expectorating. On sampling each tastant, participants were asked to identify the taste quality detected (taste identification task; potential answers were: sweet, salty, sour, bitter,

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savoury, metallic or none) and rate the strength of the tastant on a 10 mm visual analogue scale from ‘water like’ (0 mm) to ‘very strong’ (10 mm) (taste intensity task). Participants were directed to rinse their mouth three times with room temperature water prior to and between sampling each tastant. Participants who had smoked within 4 hours or eaten within 30 min were excluded from taste assessment. Taste measurements were performed on both CKD patients and control subjects. A short, validated, sodium-targeted food frequency questionnaire (FFQ) (Charlton et al., 2007) was collected to assess sodium intake. This questionnaire includes a list of 40 foods/food types that have been previously found to contribute sodium to the diet (e.g. white bread, processed breakfast cereal, processed meat, added salt; full list of foods available in Charlton et al., 2007). Some alterations were made to the food list from the original version to make it more relevant to the Australian food supply (e.g. ‘Jerky’ instead of ‘Biltong’ and adding popular Australian brand names instead of South African brand names). Participants indicated how often they consumed each of these foods, choosing from a range of frequencies (e.g. never, one to three times per week, four to eight times per week, once per day, twice per day, thrice per day). To classify participants as having a high versus low sodium intake, a cut-off of 100 mmol/day was used, in line with current sodium intake targets for people with CKD (Ash et al., 2006; Fouque et al., 2007; Levin et al., 2008; Voss, 2005). Clinically available data were collected from the CKD subjects’ medical records including age, gender, weight, height, presence of diabetes and eGFR. Body mass index was calculated by body weight divided by height squared (kg body weight/height in metres2).

Statistical analysis All values are expressed as mean ± standard deviation (SD) with normally distributed data or median (interquartile range (IQR)) for non-normal data. Identification and intensity for each of the five basic tastes was analysed individually. In addition, an overall score for taste identification was calculated by addition of the number of tastes identified correctly (range 0 to 5), and an overall score for taste intensity was calculated by averaging the intensity of the five individual taste intensity scores from the visual analogue scale (scale 0 to 10). Differences between groups (CKD versus controls; high versus low sodium intake) were analysed using chi square for categorical variables (correct identification of sweet, sour, bitter, umami, salty) and independent samples t-test for continuous variables (overall correct for taste identification task, and taste intensity score variables). Multivariate analysis was conducted to adjust for age and gender differences between CKD group and control group using logistic regression for categorical taste variables and linear regression for continuous taste variables. P-values < 0.05 were considered significant. Statistical analysis was performed using STATA v12.

Results Patient characteristics Ninety-one CKD subjects and 30 control subjects completed the study and were included for analysis (Table 1). Mean (±SD) eGFR in the CKD group was 33.1 ± 12.7 ml/min/1.73 m2, with 57% in CKD Stage 3 (n = 52/91), 34% CKD Stage 4 (n = 34/91) and 5% CKD Stage 5 (n = 5/91). Participants in the CKD group were significantly older than control subjects and there was a higher proportion of males in the group when compared with controls (Table 1).

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E.J. McMahon et al./Appetite 83 (2014) 236–241

Table 1 Subject characteristics of the CKD (n = 91) and control (n = 30) groups in the TASTE CKD Study. Characteristics

CKD

Controls

p

Age (years) Gender (male) Weight (kg) BMI (kg/m2)

65.9 ± 13.5 78% (n = 71/91) 89.3 ± 22.1 30.6 ± 6.4

55.2 ± 7.4 47% (n = 14/30) 87.3 ± 19.0 29.7 ± 6.2

100 mmol/day) (Table 2), indicating higher sensitivity of the umami and bitter tastes in this group.

Taste intensity task Discussion Mean values for taste intensity assessment are shown in Fig. 2. The umami tastant was rated significantly less intense by the CKD group compared with controls.

100

*

90 80

Percent (%)

70

The TASTE CKD study was an exploratory study aiming to assess taste function in CKD patients and compare with controls without

*

60

CKD group

50

Controls

40 30 20 10 0 Sour

Salty

Sweet

Umami

Bitter

Taste Bars indicate proportion of participants who identified the tastant correctly (unadjusted data). *Denotes significance between groups set at p

Taste perception in kidney disease and relationship to dietary sodium intake.

Taste abnormalities are prevalent in Chronic Kidney Disease (CKD) potentially affecting food palatability and intake, and nutrition status. The TASTE ...
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