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A Comparison of the Glycemic Index (Gi) Results Obtained from Two Techniques on a Group of Healthy and a Group of Mixed Subjects

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A Comparison of the Glycemic Index (Gi) Results Obtained from Two Techniques on a Group of Healthy and a Group of Mixed Subjects A COMPARISON OF THE GLYCEMIC INDEX (GI) RESULTS OBTAINED FROM TWO TECHNIQUES ON A GROUP OF HEALTHY AND A GROUP OF MIXED SUBJECTS by Elizabeth Delport Submitted in fulfillment of the requirements of the MAGISTER IN DIETETICS in the FACULTY OF HEALTH SCIENCES UNIVERSITY OF PRETORIA PRETORIA MAY 2006 Promoter: GJ Gericke ACKNOWLEDGEMENTS I would like to thank the following persons from the bottom of my heart: The Lord without Whom this research would not have been completed Ms Gerda J Gericke for your valuable guidance and support throughout the duration of the study Prof HT Groeneveld for your guidance in and statistical processing of the data Sam Mawson and Michelle van den Berg for your invaluable technical assistance Anne and Pete Grantham for perusing the document for grammatical correctness Dr Mark Wickham and his team of medical technologists at Du Buisson and Partners Pathologists - for the generous sponsorship and friendly assistance during part one of the study Pioneer Food Group and specifically Bokomo Breakfast Foods, Ceres Fruit Juices and Sasko Milling and Baking for your generous sponsorship of the study Novo Nordisk for your handsome sponsorship of the study All the test subjects for your sacrifice, diligence and selfless testing during part one and two of the study Elizabeth Combrink and Marinda Venter, my partners at our consulting rooms, for standing in for me so often during all the times I had to take study leave My husband, children, parents and friends for your prayers, encouragement and support during the course of the study i TABLE OF CONTENTS Abstract Page List of Tables vi List of Figures viii List of Addenda xi List of Abbreviations xii Abstract xiii 1. BACKGROUND TO THE STUDY 1 1.1 The Glycemic Index and its use 1 1.2 Substantiation of the research 2 1.3 Investigation 4 2. LITERATURE REVIEW 5 2.1 Introduction 5 2.2 Historical perspective 5 2.2.1 Pioneers 5 2.2.2 Coining of the concept 6 2.2.3 Measurement and interpretation 6 2.2.4 Arguments against the use of GI values 7 2.2.4.1 Lack of agreement in GI values obtained between different centers 7 2.2.4.2 Individual variation in glycemic responses 8 2.2.4.3 Glycemic response of mixed meals 8 2.2.4.4 The use of 50g carbohydrate portion sizes in GI testing 11 2.2.4.5 Lack of demonstration of long-term benefits of low GI foods 11 2.2.4.6 The GI and its complexity 11 2.2.4.7 Insulin response versus glycemic response 12 2.2.4.8 Sucrose versus starch: different effects on body weight, lipidemia and 12 glycemia ii 2.2.5 Driving forces 12 2.3 Current Scenario 13 2.3.1 Application and clinical use of GI values 13 2.3.1.1 Dietary GI in relation to metabolic risk factors and incidence of lifestyle 13 diseases 2.3.1.2 Mood and cognitive performance 23 2.3.1.3 Sports performance 23 2.3.2 Need for expanding food lists 26 2.4 Evolution of measurement 26 2.4.1 Reflection on methodology and interpretation 26 2.4.1.1 Techniques 26 2.4.1.2 Validity and reliability 28 2.4.1.3 Advantages 34 2.4.1.4 Limitations 34 2.4.1.5 Grey areas 37 2.4.2 Other relevant concepts 39 2.4.2.1 Insulin Index (II) 39 2.4.2.2 Glycemic Load (GL) 40 2.4.2.3 RAG and SAG measures 40 2.4.3 Factors influencing the glycemic response to foods and the variability of the 41 GI of a food 2.4.3.1 Factors influencing the blood glucose response to foods 41 2.4.3.2 Factors influencing the variability of the GI values of foods 49 2.5 Need for standardized measurement 66 2.6 Conclusion from literature 66 iii 3. RESEARCH DESIGN AND METHODOLOGY 69 3.1 Aim of the study 69 3.2 Part 1 69 3.2.1 Background information 69 3.2.2 Research problem 69 3.2.3 Sub-problems 70 3.2.4 Hypotheses 71 3.2.5 Study design 71 3.2.6 Materials and methods 72 3.2.7 Statistical analysis 75 3.3 Part 2 81 3.3.1 Background information 81 3.3.2 Research problem 81 3.3.3 Sub-problems 81 3.3.4 Hypotheses 82 3.3.5 Study design 82 3.3.6 Materials and methods 83 3.3.7 Statistical analysis 84 4. RESULTS AND DISCUSSION 85 4.1 Part 1 85 4.1.1 Sub-problem 85 4.1.2 Sub-problem 89 4.1.2.1 GI Values 89 4.1.2.2 AUC Values 97 4.1.3 Sub-Problem 109 4.1.3.1 AUC Minimum (AUCmin) 109 4.1.3.2 Total AUC (AUC0) 111 iv 4.1.4 Research Problem 116 4.1.4.1 Muesli 116 4.1.4.2 Apple juice 119 4.2 Part 2 121 4.2.1 Sub-problem 121 4.2.2 Sub-problem 128 4.2.3 Research problem 132 4.3 Reflection on hypotheses 138 4.4 Limitations of the study 141 5. CONCLUSION AND RECOMMENDATIONS 142 REFERENCES 146 ADDENDA 152 v Abstract This comparative study was conducted in two parts. Part 1 Objectives • To compare the mean GI-values of two foods, i.e. Muesli (M) and Apple juice (A) from a mixed group of subjects (healthy, type 1 and type 2 diabetic), using the Medisense Precision QID Glucometre (MPQIDG) extra-laboratory (EL) to the mean GI-values of the same two foods from a group of healthy subjects intra-laboratory (IL), using laboratory equipment (YSI Analyser or YSI) and the MPQIDG, and determine whether the former method is an acceptable alternative for the latter. • To compare the Area under the curve (AUC), their means and GI values of each healthy subject, using the YSI and MPQIDG (IL). Subjects and Methodology A group of 12 trained subjects, aged 29-54 years (41+7), BMI 18-30 kg/m2 (24+4), were tested IL (Group 1) under well-controlled conditions, as recommended by the FAO/WHO (1998).(3) M and A were each tested once and the reference food (glucose) was tested on 3 occasions, using the MPQIDG and the YSI. Capillary blood glucose was measured fasting and every 15min for 2h, after the glucose/test food was consumed (diabetic subjects measured blood glucose concentrations over 3h). Mean GI-values of M and A, obtained IL by Group 1 were compared to the mean GI-values of M, obtained EL by a mixed group of subjects (Group 3), and of A, obtained EL by another mixed group of subjects (Group 4), and the mean GI-values of M and A, obtained EL by the group of 12 healthy subjects (Group 2), using ANOVA. The AUC and GI values of each healthy subject of Group 1 were compared using Pearson’s correlation coefficient (r). Lin’s concordance correlation coefficient (rc) was used for testing agreement (4). Statistical significance was set at p=0.05. Results The mean GI-values of M and A, as determined by Groups 1, 2, 3 and 4 (using ANOVA) did not differ significantly for M (p( =0.2897) and A (p=0.8454). Pearson’s correlation coefficient (r) was acceptable and significant for the AUC-values of Glucose 1 (r=0.7; p=0.0081), good and significant for the GI-value of A (r=0.8; p=0.0043) and very good and highly significant for the AUC-values of Glucose 2 (r=0.9; p<0.0001), Glucose 3 (r=0.9; p<0.0001), M (r=0.9; p<0.0001) and A (r=0.9; p<0.0001) and the GI-value of M (r=0.9;p=0.0003), respectively, after removal of outliers. The mean AUCMPQIDG of all the foods tended to be higher than the mean AUCYSI, after removal of outliers, but this was not significant (p=0.69301; p=0.20838; p=0.43311; p=0.32926; p= 0.49199 for Glucose 1, 2 , 3 M and A, respectively). Lin’s concordance correlation coefficient [which tests reproducibility/agreement (rc)] was acceptable for the AUC-value of Glucose 1 (rc=0.7) and the GI-value of A (rc=0.7), good for the AUC-value of Glucose 2 (rc=0.8) and very good for the AUC-value of Glucose 3 (rc=0.9), M (rc=0.9) and A (rc=0.9) and the GI-value of M (rc=0.9), respectively, after removal of outliers. vi Part 2 Objective To compare the GI-values from a mixed group of subjects using the MPQIDG, EL with GI-values from a group of healthy subjects IL, using laboratory equipment laboratories A-E who took part in an inter- laboratory study(39) and determine whether the former method is an acceptable alternative for the latter. Subjects and methodology A mixed group of 10 trained subjects (5 male: 2 diabetic and 3 healthy; 5 female: 3 diabetic and 2 healthy) were tested EL under well-controlled conditions, as recommended by the FAO/WHO (1998)(3) The test foods were White bread, Barley, Rice, Instant potato and Spaghetti (reference food: glucose). Capillary blood glucose concentrations were measured fasting and every 15min after the glucose/test food was consumed for 2h (healthy subjects) and 3h (diabetics), using the MPQIDG. Mean GI-values were compared to the weighted mean GI-values of the 5 laboratories (laboratories A–E), using the analysis of variance (paired t-test).
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