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The Journal of Nutrition Vol. 129 No. 1 January 1999,
pp. 122-125
Human Nutrition Unit GO8, University of Sydney, New South Wales 2006, Australia
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ABSTRACT |
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Abstract
Introduction
Methods
Results
Discussion
References
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Decreased taste sensitivity may be one of the many factors influencing the poor nutritional status of many patients with chronic renal failure. Several studies examining taste in chronic uremic and hemodialysis (HD) patients indicate decreased sensitivity; continuous ambulatory peritoneal dialysis (CAPD) patients, however, warrant investigation. The aim of this study was to determine if the taste detection threshold for each of the four tastes (sweet, salty, sour and bitter) differs between CAPD patients and age and sex matched controls with normal renal function. The thresholds were determined using Cornsweet's staircase technique for increasing and decreasing stimulus concentration, in which the subject's response determines the next concentration to be tested. A forced-choice design using three samples was used to help minimize bias. The taste detection threshold for the CAPD patients was significantly higher than that of the controls for sodium chloride (salty)(P = 0.001) and quinine (bitter) (P = 0.01). This information may be useful when designing dietary supplements and devising meal plans to help patients consume nutritionally adequate diets.
KEY WORDS: continuous ambulatory peritoneal dialysis · hemodialysis · detection threshold · recognition threshold · taste sensitivity · humans
Patients with renal failure have decreased taste sensitivity (Atkin-Thor et al. 1978 Continuous ambulatory peritoneal dialysis (CAPD) is increasingly the first line of renal replacement therapy, but few studies have examined taste in CAPD patients. Because the dialysis process differs from HD, it cannot be assumed that taste will be affected in the same way. CAPD involves a steady state of solute removal, whereas the intermittent nature of HD results in greater fluctuation in solute concentrations.
Inadequate dietary intake is one factor contributing to poor nutritional status (Allman et al. 1990 The most traditional way of assessing taste function is threshold sensitivity. Taste sensitivity can be measured in two ways, taste detection and recognition threshold. The taste detection threshold is defined as the lowest concentration of a solution that can be distinguished from water. The recognition threshold is the lowest concentration of a solution at which the taste sensation such as sweet can be recognized.
The objective of this study was to test the hypothesis that renal patients receiving CAPD have a higher detection threshold for one or more of the four tastes than do matched controls.
Subjects.
A total of 36 subjects were studied. The selection criteria for all of the subjects included the following: nonsmokers, absence of a chronic disease that could affect taste (such as cancer or insulin-dependent diabetes) and having received CAPD for at least 2 mo.
Taste testing procedure.
The solutions used for the evaluation of taste detection threshold were sucrose (CSR, Sydney, Australia) for sweet, sodium chloride (Saxa, Sydney, Australia) for salty, citric acid (David Craig and Co., Sydney, Australia) for sour and quinine dihydrochloride (Ophthalmic Labs, Sydney, Australia) for bitter. All solutions were made with demineralized water as solvent. Table 1 lists the concentrations of each solution. All solutions were freshly made every 2 d and served to each subject at room temperature. The testing cups were made of plastic (Solo Cups, Chicago, IL).
Data analysis.
Data were analyzed using Statview (version 4.02, Abacus Concepts, Berkeley, CA). A mean taste detection threshold and SD was calculated for each group and a comparison was made between the two. The Wilcoxon rank-sign test was used to assess whether the taste detection thresholds were different between the two subject groups (Altman 1991 Table 2 summarizes the demographic and clinical characteristics of the two groups.
Patients receiving CAPD demonstrated higher taste detection thresholds than controls for NaCl (salty) and quinine (bitter). The thresholds found are higher than those reported for normal subjects and renal patients (Bales et al. 1986
INTRODUCTION
Abstract
Introduction
Methods
Results
Discussion
References
, Brouns Schiro and Eveleen Olin 1988, Burge et al. 1979, Ciechanover et al. 1980, Fornari and Avram 1978, Shepherd et al. 1986, Vreman et al. 1980). The four qualities of taste are sweet, salty, sour and bitter. Both patients with chronic uremia and those undergoing hemodialysis (HD) have been studied, and sweet and sour have commonly been shown to be affected. Taste improves immediately after a dialysis session although not to normal levels (Burge et al. 1979, Ciechanover et al. 1980, Fornari and Avram 1978, Shepherd et al. 1986 and 1987), implicating an accumulation of toxins between dialyses in the etiology; however, the responsible toxins have not been determined (Getchell 1991).
). Taste influences food palatability and appetite; however, this link between taste sensitivity and food consumption is largely unstudied in renal patients. One study in HD patients demonstrated that improvement in taste acuity (by zinc supplementation) was accompanied by an increase in energy intake of 2.8 MJ/d (Atkin-Thor et al. 1978). It was necessary to obtain baseline data on taste acuity in CAPD patients before investigation into the presence of a relationship with food intake was undertaken (Fernstrom et al. 1996, Smith Hurley et al. 1987).
MATERIALS AND METHODS
Abstract
Introduction
Methods
Results
Discussion
References
View this table:
Table 1.
Concentration of solutions used to determine taste
detection threshold1
, Fornari and Avram 1978, Grzegorczyk et al. 1979, Vreman et al. 1980, Weiffenbach et al. 1982).
). A change in response from correct to incorrect or visa versa was designated a turn. Testing continued until six turns were recorded. The taste detection threshold for each subject was taken as the average of the last four concentrations at which a turn occurred. The taste detection threshold for each subject was assigned a rank number; for example, if the threshold found was between the first and the second concentration values, the rank assigned was a one. Multiple values for taste detection threshold by a tester at a given time were shown to be reproducible to within one rank for 100% of tests and to the same rank for at least 75% of the tests. This is in agreement with the findings of others (American Society for Testing of Materials 1985b).
). A probability of P < 0.01 was taken as an acceptable level of significance because four tests were conducted. Simple linear regression was used to examine the relationship between the taste detection threshold and length of time receiving CAPD, serum urea and creatinine and age (Altman 1991). Body mass indices of the two groups were compared using the unpaired t test.
RESULTS
Abstract
Introduction
Methods
Results
Discussion
References
View this table:
Table 2.
Demographic and clinical characteristics of the subjects1
View larger version (30K):
[in a new window]
Fig 1.
Taste detection threshold of continuous ambulatory peritoneal patients and controls. Values are mean rank ± SD, n = 18. Asterisks indicate values significantly different from those of patients, *P = 0.01,**P = 0.001.
DISCUSSION
Abstract
Introduction
Methods
Results
Discussion
References
, Fornari and Avram 1978, Grzegorczyk et al. 1979, Vreman et al. 1980, Weiffenbach et al. 1982). This study used three samples in each trial, whereas most studies use only two samples, increasing the probability of guessing the correct answer. Therefore, higher thresholds are obtained when using three samples (Grzegorczyk et al. 1979).
studied the four tastes by assessing recognition thresholds in 17 CAPD patients. Compared with controls, the patients' bitter taste was impaired, but no difference was detected for salty taste. The differences between that study and ours may reflect subject variability or the use of different methods. In a pilot study of 12 patients by our group (I. Van der Eijk, Student University of Maastricht, personal communication), the recognition threshold for salty was higher in the patients but the detection threshold was not impaired. However, this study used only two samples in each trial.
also found that CAPD patients had a preference for salty foods. It is plausible that if people are less sensitive to the salty taste, they will require a greater concentration of the substance compared with controls and hence might prefer saltier foods. However, the link between sensitivity and salt intake has not been substantiated (Mattes 1984).
, Mattes 1997). To elicit a salty sensation, this level must be exceeded by a given amount (Mattes 1984). Therefore, an individual with an increased salivary sodium concentration would have a higher threshold for salty. However, in the current study, serum sodium and salivary sodium were not measured; thus correlations between these and the salty detection threshold could not be identified. It is possible that sodium levels in the dialysate could affect taste threshold.
also found CAPD patients to have a decreased sensitivity to bitter taste. However, the explanation for the dysfunction of taste acuity for bitter in CAPD patients is unknown. Among the explanations for renal patients having impaired taste are metabolic disturbances, deficiencies of multiple micronutrients due to decreased food intake (zinc deficiency has been frequently implicated, Atkin-Thor et al. 1978, Burge et al. 1984, Shepherd et al. 1986, Vreman et al. 1980), kidney dysfunction and alterations of peripheral nerve function (Getchell 1991). Drugs may also either decrease or increase the sensitivity to a certain taste; thus medication remains a confounding variable in most studies of taste in renal patients (Van Der Eijk and Allman-Farinelli 1997). However, neither the reasons for impaired taste nor the effects of medication have been elucidated or specifically related to CAPD patients.
, Grzegorczyk et al. 1979, Moore et al. 1982, Spitzer 1988, Weiffenbach et al. 1982). They have found that older people have a higher taste sensitivity threshold. This effect was demonstrated only for the detection threshold for sucrose (sweet) in this study. The effect of age does not bias these results because the patients and controls were matched for age. Previous studies of renal patients (Burge et al. 1979, Fernstrom et al. 1996) indicated that as serum urea rises, the taste sensitivity diminishes. However, in this study, no relationship with either urea or creatinine was found.
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FOOTNOTES |
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Manuscript received 23 December 1997. Initial reviews completed 20 March 1998. Revision accepted 8 October 1998.
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ACKNOWLEDGMENTS |
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We are grateful to Ingrid Van Der Eijk who did the preliminary work that enabled the current study and to P. Lyons Wall for sharing her expertise on taste testing. We also thank Adrian Gillan and the staff at Dame Edith Walker, Dialysis Training Center, Central Sydney Area Health Service for their cooperation and assistance and also all of the subjects who participated in the study.
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LITERATURE CITED |
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Abstract
Introduction
Methods
Results
Discussion
References
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