Sweet Taste Sensitivity in Diabetics and Controls: A Study
Sweet Taste Sensitivity in Diabetics and Controls: A Study
In this analytical cross sectional study, taste thresholds were compared in pre-diabetics with age, sex and body mass index (BMI) matched T2DM patients and with normoglycemic controls. Although a total of 191 subjects were studied, data of only 40 pre-diabetics, 40 diabetics and 34 normoglycemics were considered for analysis due to stringent matching of confounding baseline characteristics.
Patients with diagnosed T2DM aged between 20–60 years, attending the family practice centre of the University of Sri Jayewardenepura, Sri Lanka during a period of 4 months were included in the diabetic group. The employees in the same university with no history of diabetes were invited to be included in the pre-diabetic and control groups and were categorized into the two groups depending on their glycated haemoglobin (HbA1C) levels. HbA1C levels were determined by the high-performance liquid chromatography method under strict quality assurance guidelines. Grouping of these subjects to pre-diabetics and normoglycemic controls was done with HbA1C using the American Diabetes Association guidelines. Individuals with mental and physical illnesses, those on medications affecting the smell and taste sensations, pregnant and lactating women and those with diseases of the oral cavity were excluded from the study.
Ethical Considerations. This study was approved by the Ethics Review Committee of the University of Sri Jayewardenepura and informed written consent was obtained from participants prior to recruitment.
Data Collection. Taste sensitivity testing was carried out in batches of 5–6 subjects per day. On the day of the tests, the participants were asked to arrive between 8 AM and 8:30 AM refraining from food, smoking, alcohol and betal chewing from 10 PM. the previous day to standardize the testing procedure with regard to the level of hunger/satiation. Standard breakfast comprising of 3 slices of brown bread with margarine and a plantain was given 1 hour before sensitivity testing. An interviewer administered questionnaire was used to obtain demographic data, dietary history which included the details of sugar consumption of the subjects, the past medical history and details of all medications of the subjects. Measurements of height and weight were recorded. Blood (5 ml) was drawn to an EDTA tube for the estimation of HbA1C and these values were used to identify pre-diabetic subjects from normoglycemic controls. Taste testing was performed in an odorless room and completed before 11 AM.
Threshold Testing. Sucrose solutions which were prepared diluting sucrose in distilled water in successive dilutions of 1/4 log and 1/2 log steps were used for the estimation of detection and recognition thresholds and for supra threshold estimations respectively. The concentration gradients which were used for sucrose detection and recognition thresholds (1.25 × 10 to 6.4 × 10 mol/L) were based on previous literature and confirmed by a pilot study done on 30 subjects. All taste thresholds were assessed by the same research assistant trained by the investigators.
Detection and recognition thresholds were determined by the multiple forced-choice presentation of freshly prepared sucrose solutions in order of ascending concentration starting from the lowest. The sucrose solution and distilled water were offered to subjects in 3 disposable cups in a pre-randomized order – two containing 10 ml distilled water and one containing 10 ml sucrose solution. They were asked to swish the solutions in the mouth for 5 seconds, spit out and pinpoint which cup contains the solution with a taste. The subjects were instructed to rinse the mouth with distilled water in between tasting the solutions to eliminate any remaining traces of sucrose in the mouth. In the event of giving an incorrect response or stating the inability to distinguish between the solution and distilled water, the subjects were presented with the next set of solutions which contained the sucrose solution with the next higher concentration of sucrose. Solutions were offered in this manner until the presence of a taste was identified correctly twice in succession. The concentration of the solution at which the participant was able to identify the presence of a taste first, was considered as the detection threshold and the concentration of the solution at which the participant was able to identify the quality of the taste first, was considered as the recognition threshold.
The perceived sensations of suprathreshold intensities of sucrose solutions presented randomly were determined by the ratings indicated by the subjects in a 230 mm visual analogue scale (VAS) graded from '0' to '100' which is a modification of the general Labeled Magnitude scale (gLMS) described in published literature. The scale which is modified to suit our population was pre-tested in the pilot study. The top and bottom ends of the vertical scale had intensity labels with descriptive adjectives, "strongest imaginable" and "barely detectable" respectively, indicated in the native language (Sinhala) of the participants. Prior to introducing the test solutions of varying concentrations, each subject was allowed to taste the two solutions with the lowest (6.4 × 10 mol/L) and the highest (2.02 mol/L) concentrations for them to familiarize with the two ends of the scale. The 4 sucrose solutions (2.02 × 10, 6.40 × 10, 2.02 × 10 and 6.40 × 10 mol/L) were randomly presented to the subjects 1 minute apart. They were asked to taste each solution for 5 s, spit out and rate the intensity of it by marking a cross on the scale taking into account the intensities perceived for concentrations representing the ends of the scale. Instructions were given to rinse the mouth with distilled water in between tasting each sucrose solution. Since each concentration was rated 3 times, the average of these ratings was considered as the intensity rating for that particular concentration.
Statistical Analysis. The sociodemographic factors were presented as counts for categorical variables and as means and standard deviations for continuous variables. As only 8% (n = 10) of the sample were smokers and also because the smokers were distributed in almost equal proportions amongst the three groups, smoking was not considered in subsequent analysis. ANOVA was performed and post hoc comparisons were made using the Tukey's procedure to compare the differences between the three groups in detection and recognition thresholds and in the amount of sugar consumed per day.
Differences in Suprathreshold ratings were analyzed using ANOVA for repeated measures with the three groups (diabetics, pre-diabetics and normoglycemic controls) as between subject factor and suprathreshold intensity ratings as within subject factor. Application of this model showed positive kurtosis. Mauchly's test indicated that the assumption of sphericity has been violated, therefore degrees of freedom were corrected using Greenhouse-Geisser estimates of sphericity (ε = 0.43). When ANOVA revealed significant effects, post hoc Tukey's analysis was conducted. The criterion for statistical significance was at p < 0.05.
Methods
Subjects
In this analytical cross sectional study, taste thresholds were compared in pre-diabetics with age, sex and body mass index (BMI) matched T2DM patients and with normoglycemic controls. Although a total of 191 subjects were studied, data of only 40 pre-diabetics, 40 diabetics and 34 normoglycemics were considered for analysis due to stringent matching of confounding baseline characteristics.
Patients with diagnosed T2DM aged between 20–60 years, attending the family practice centre of the University of Sri Jayewardenepura, Sri Lanka during a period of 4 months were included in the diabetic group. The employees in the same university with no history of diabetes were invited to be included in the pre-diabetic and control groups and were categorized into the two groups depending on their glycated haemoglobin (HbA1C) levels. HbA1C levels were determined by the high-performance liquid chromatography method under strict quality assurance guidelines. Grouping of these subjects to pre-diabetics and normoglycemic controls was done with HbA1C using the American Diabetes Association guidelines. Individuals with mental and physical illnesses, those on medications affecting the smell and taste sensations, pregnant and lactating women and those with diseases of the oral cavity were excluded from the study.
Ethical Considerations. This study was approved by the Ethics Review Committee of the University of Sri Jayewardenepura and informed written consent was obtained from participants prior to recruitment.
Data Collection. Taste sensitivity testing was carried out in batches of 5–6 subjects per day. On the day of the tests, the participants were asked to arrive between 8 AM and 8:30 AM refraining from food, smoking, alcohol and betal chewing from 10 PM. the previous day to standardize the testing procedure with regard to the level of hunger/satiation. Standard breakfast comprising of 3 slices of brown bread with margarine and a plantain was given 1 hour before sensitivity testing. An interviewer administered questionnaire was used to obtain demographic data, dietary history which included the details of sugar consumption of the subjects, the past medical history and details of all medications of the subjects. Measurements of height and weight were recorded. Blood (5 ml) was drawn to an EDTA tube for the estimation of HbA1C and these values were used to identify pre-diabetic subjects from normoglycemic controls. Taste testing was performed in an odorless room and completed before 11 AM.
Threshold Testing. Sucrose solutions which were prepared diluting sucrose in distilled water in successive dilutions of 1/4 log and 1/2 log steps were used for the estimation of detection and recognition thresholds and for supra threshold estimations respectively. The concentration gradients which were used for sucrose detection and recognition thresholds (1.25 × 10 to 6.4 × 10 mol/L) were based on previous literature and confirmed by a pilot study done on 30 subjects. All taste thresholds were assessed by the same research assistant trained by the investigators.
Detection and recognition thresholds were determined by the multiple forced-choice presentation of freshly prepared sucrose solutions in order of ascending concentration starting from the lowest. The sucrose solution and distilled water were offered to subjects in 3 disposable cups in a pre-randomized order – two containing 10 ml distilled water and one containing 10 ml sucrose solution. They were asked to swish the solutions in the mouth for 5 seconds, spit out and pinpoint which cup contains the solution with a taste. The subjects were instructed to rinse the mouth with distilled water in between tasting the solutions to eliminate any remaining traces of sucrose in the mouth. In the event of giving an incorrect response or stating the inability to distinguish between the solution and distilled water, the subjects were presented with the next set of solutions which contained the sucrose solution with the next higher concentration of sucrose. Solutions were offered in this manner until the presence of a taste was identified correctly twice in succession. The concentration of the solution at which the participant was able to identify the presence of a taste first, was considered as the detection threshold and the concentration of the solution at which the participant was able to identify the quality of the taste first, was considered as the recognition threshold.
The perceived sensations of suprathreshold intensities of sucrose solutions presented randomly were determined by the ratings indicated by the subjects in a 230 mm visual analogue scale (VAS) graded from '0' to '100' which is a modification of the general Labeled Magnitude scale (gLMS) described in published literature. The scale which is modified to suit our population was pre-tested in the pilot study. The top and bottom ends of the vertical scale had intensity labels with descriptive adjectives, "strongest imaginable" and "barely detectable" respectively, indicated in the native language (Sinhala) of the participants. Prior to introducing the test solutions of varying concentrations, each subject was allowed to taste the two solutions with the lowest (6.4 × 10 mol/L) and the highest (2.02 mol/L) concentrations for them to familiarize with the two ends of the scale. The 4 sucrose solutions (2.02 × 10, 6.40 × 10, 2.02 × 10 and 6.40 × 10 mol/L) were randomly presented to the subjects 1 minute apart. They were asked to taste each solution for 5 s, spit out and rate the intensity of it by marking a cross on the scale taking into account the intensities perceived for concentrations representing the ends of the scale. Instructions were given to rinse the mouth with distilled water in between tasting each sucrose solution. Since each concentration was rated 3 times, the average of these ratings was considered as the intensity rating for that particular concentration.
Statistical Analysis. The sociodemographic factors were presented as counts for categorical variables and as means and standard deviations for continuous variables. As only 8% (n = 10) of the sample were smokers and also because the smokers were distributed in almost equal proportions amongst the three groups, smoking was not considered in subsequent analysis. ANOVA was performed and post hoc comparisons were made using the Tukey's procedure to compare the differences between the three groups in detection and recognition thresholds and in the amount of sugar consumed per day.
Differences in Suprathreshold ratings were analyzed using ANOVA for repeated measures with the three groups (diabetics, pre-diabetics and normoglycemic controls) as between subject factor and suprathreshold intensity ratings as within subject factor. Application of this model showed positive kurtosis. Mauchly's test indicated that the assumption of sphericity has been violated, therefore degrees of freedom were corrected using Greenhouse-Geisser estimates of sphericity (ε = 0.43). When ANOVA revealed significant effects, post hoc Tukey's analysis was conducted. The criterion for statistical significance was at p < 0.05.
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