Original Research

The Effect of a Low Glycaemic Index Breakfast on Blood Glucose, Insulin, Lipid Profiles, Blood Pressure, Body Weight, Body Composition and Satiety in Obese and Overweight Individuals: A Pilot Study Sebely Pal, PhD, Siew Lim, BSc, and Garry Egger, PhD School of Public Health; ATN Centre for Metabolic Fitness, Curtin University, Perth Western Australia, (S.P., S.L.), Health and Applied Sciences, Southern Cross University, New South Wales (G.E.), AUSTRALIA Key words: obesity, glycaemic index, energy intake, body composition, blood glucose, total cholesterol, lipoproteins, triacylglycerol Background: Low glycaemic index (GI) carbohydrates have been shown to have favourable effects on blood glucose, lipid profiles and satiety in individuals with chronic disease. However, modifying GI for the entire diet may be too complicated for an average individual without professional support. This study aims to investigate the health benefits of changing the GI index of a single meal a day, a more achievable goal. Objective: The objective of this study was to investigate whether altering the GI of one meal/day (breakfast meal only) for 21 days in obese individuals would have a favourable effect on fasting serum glucose, low density lipoproteins, high density lipoproteins, insulin and triglycerides. Design: A randomised, crossover design was used to compare the effects of a high GI with a low GI breakfast replacement meal. The macronutrient compositions of the breakfasts were matched. The subjects, 16 women and 5 men, who were overweight or obese, were randomly allocated to two intervention periods of 21 days each separated by a washout interval of 21 days. Subjects were seen at the beginning (baseline) and end of each intervention period (final). Results: The change in fasting glucose (baseline versus final data) during the Low GI period was significantly lower (p ⬍ 0.05) from that during the High GI period). Fasting triglycerides, insulin and fasting total, HDL LDL cholesterol were unaffected by the daily changes in the type of breakfast. The change in satiety ratings before lunch (baseline versus final) during the Low GI period was slightly higher from that during the High GI period. Conclusion: Results of this study show beneficial changes in fasting glucose and satiety by modifying the GI of a single meal per day, suggesting such modifications could potentially be a useful public health recommendation.

INTRODUCTION

Studies have shown that dietary fat is associated with obesity and a low fat diet was effective in weight loss in some people [2,3]. However, the steady increase in the obesity rate in spite of the (apparent) decrease in fat consumption in recent decades suggests that other dietary factors may be involved [4]. It has recently been suggested the reason these low fat, high carbohydrate diets may be ineffective is that high carbohydrate diets may incorporate foods that promote a high glycemic response (a rapid increase in blood glucose concentration). Such foods may alter appetite and energy partition in a manner that is conducive to fat gain [5].

Obesity is a major health problem worldwide. Obesity has reached epidemic proportions globally, with more than 1 billion adults overweight with at least 300 million of them clinically obese. Obesity is associated with a number of metabolic disorders including coronary heart disease, hypertension, stroke, certain cancers, non-insulin diabetes mellitus, gallbladder disease, and dyslipidemia [1]. Dietary intervention is one of the main aspects in the management of this epidemic.

Address reprint requests to: Associate Professor Sebely Pal, Department of Nutrition, Dietetics and Food Science, School of Public Health, Curtin University of Technology, Kent Street, Bentley, Western Australia 6102, AUSTRALIA. E-mail: [email protected]

Journal of the American College of Nutrition, Vol. 27, No. 3, 387–393 (2008) Published by the American College of Nutrition 387

Effect of a Low Glycaemic Index Breakfast Increasing evidence is now showing that the quality and quantity of carbohydrates may play a significant role in the development of chronic diseases [6 – 8]. Diets with a high glycemic load, which lead to increased glycemic and insulinemic response after consumption, may contribute to the development of insulin resistance, a primary cause of the metabolic syndrome [5]. Studies have also shown that a low GI diet is associated with lower fasting plasma LDL cholesterol, fasting triglyceride, and postprandial glucose concentrations and increase in fasting plasma HDL concentrations [6 –12]. Given that overweight and obese people are at greater risk of developing diabetes and cardiovascular disease, changing GI of foods may favourably influence their health prospect by conferring benefits to their blood glucose and lipid profile. Furthermore, evidence suggests that low dietary GI leads to increased satiety and decreased energy intake [13]. If this leads to a reduction in body weight, a further reduction in health risks could be seen. Most intervention studies examining the effect of glycaemic index on blood glucose, lipids and body composition have been conducted in diabetic subjects [6,11,14]. Therefore, the beneficial effects of this type of diet on risk factors are unknown in nondiabetic, overweight subjects. In addition, many of the studies to date have focused on altering the GI of all meals. Modifying total dietary GI of all meals during the day may be an unattainable goal for some individuals. We propose that changing the GI of one meal may be more practical and therefore may have a greater compliance by individuals, but no study has been done to assess the benefits of a single low GI meal a day on satiety, blood glucose, and lipids. Therefore, the aim of this study was to investigate whether altering the GI of one meal for 21 days in obese individuals would have a favourable effect on satiety, fasting serum glucose, insulin, LDL, HDL and TG.

the community using poster advertising and radio. Subjects were screened for plasma cholesterol concentrations of ⱖ5.5mmol/L. Subjects with hypercholesterolemia were recruited so that we could examine whether a low GI breakfast could have a lipid lowering effect. This effect may be harder to observe in subjects with normal lipid levels. All subjects who met these inclusion criteria underwent a medical examination. Exclusion criteria included current chronic medical disease, pregnancy, hormone replacement therapy, lipid-lowering medication, use of steroids and other agents that may influence lipid metabolism, use of warfarin, smoking, hyper- or hypothyroidism, diabetes mellitus, cardiovascular events within last 6 months, psychological unsuitability, major systemic diseases, gastrointestinal problems, proteinuria, liver and renal failure, and apolipoprotein genotype (E2/E2 exclusion). Clinical features and anthropometric measures of the twenty-one subjects who completed the study are given in Table 1. All procedures were approved by the Ethics Committee of Curtin University and conformed to the Helsinki Declaration. Subjects provided written informed consent prior to participation in the study.

Study Design This is a randomised crossover single-blinded study examining the effects of low GI or high GI breakfast on satiety, lipid and glucose metabolism and body composition. Twenty one participants were randomly allocated to two intervention periods of either high GI or low GI breakfast for 21 days. The two intervention periods were separated by a washout interval of 21 days. Subjects were seen at the beginning (baseline) and end of each intervention period (final).

Experimental Protocol

SUBJECTS AND METHODS Subjects Twenty one obese or overweight volunteers (5 men 16 women), aged between 25 and 65 years, were recruited from

Initially, subjects arrived at Curtin University after a 10 –12 hour fast for baseline measurements. After a rest period of 30 minutes, fasting blood samples were drawn by venepuncture for analysis of blood glucose and lipids. Blood pressure and heart rate were measured on the right arm using an automatic

Table 1. Baseline Characteristics of Subjects1

Body weight (kg) BMI (kg/m2) Hip (cm) Waist (cm) Fasting triglycerides (mmol/L) Fasting total cholesterol (mmol/L) Fasting HDL-cholesterol (mmol/L) Fasting LDL-cholesterol (mmol/L) Fasting glucose (mmol/L) Fasting insulin (␮IU/ml) HOMA score 1

Group 1 (low) (n ⫽ 10)

Group 2 (high) (n ⫽ 11)

84.05 ⫾ 4.85 32.8 ⫾ 0.95 111.28 ⫾ 5.63 100.02 ⫾ 6.56 1.55 ⫾ 0.21 6.33 ⫾ 0.28 1.98 ⫾ 0.14 2.91 ⫾ 0.21 5.11 ⫾ 0.10 5.45 ⫾ 0.80 1.23 ⫾ 0.22

85.34 ⫾ 420 30.5 ⫾ 0.22 111.49 ⫾ 448 101.25 ⫾ 2.57 1.53 ⫾ 0.15 6.35 ⫾ 0.4 1.97 ⫾ 0.18 2.98 ⫾ 0.35 5.12 ⫾ 0.12 5.38 ⫾ 0.93 1.22 ⫾ 0.26

Data represented as means ⫾ s.e.m.

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Effect of a Low Glycaemic Index Breakfast Table 2. Food Composition of Test Meals Constituent

Low GI breakfast

High GI breakfast

Cereal Milk Bread Margarine Fruit Extras

1/3 cup All bran fruit ‘n oat 100 ml skim (fat ⬍ 0.16%) 1 slice Oat bran and Honey 1 tsp reduced fat polyunsaturated margarine 2 dried apricots 1/2 tsp honey

1 cup Corn Flakes 100 ml low fat (fat ⬍ 1%) 1 slice wholemeal bread 1 tsp polyunsaturated margarine 3–4 slices banana None

wrist manometer (Omron R6) after the subjects had sat quietly for 5 minutes. Weight and percentage body composition measurements were taken using Tanita scales (USA), with patients dressed in light clothing without shoes. Body composition was also measured using the RJL Systems BIA - 101 Body Composition Analyzer (USA). This system allows the measurement of percentage body fat via bioelectrical impedance. Height measurements were taken using a mechanical stadiometer (Surgical and Medical Products, Hills, Australia. BMI (kg/m2) was calculated from weight and height measurements. Waist (at umbilicus) and hip circumference were measured from which Waist to Hip ratio (WHR) was calculated. After baseline measurements, the subjects were then randomised to a 3-week intervention period consisting of breakfast meals of either low GI or high GI (Table 2). Subjects were to maintain their habitual intakes for the other meals (ad libitium). Dietary intake over the course of the trial was monitored through the completion of 3-day food diaries at the beginning and end of each intervention period. Subjects recorded their dietary intake during the 1st three consecutive days before baseline and last 3 consecutive days (day 19 –21) before final measurements. At the end of each intervention period, subjects arrive at Curtin University for final measurements, and protocol is as with baseline measurements.

Diets Both breakfast meals supplied the same energy, protein, fat and carbohydrate values ⫾ 6%, thus making GI the only variables. For all other meals of the day, subjects were instructed to maintain their normal eating behaviour. All subjects were asked to consume a low GI or high GI breakfast at 08:30 and usual lunch at 12:30. The high GI breakfast was based on wholemeal bread and a high GI cereal, the low GI on oat bran based bread and a low GI cereal. Macronutrient levels were matched by adjusting the fat content of milk and margarine and sugar content was varied by the addition of fruits and honey. The constituents and macronutrient content of the two breakfast meals are shown in Tables 2 and 3 respectively. All food items for breakfast were provided to subjects for the duration of the study to increase compliance. In addition, follow-up calls were made every 3 days to subjects to assist with compliance. Composition of the reported diet (mean ⫾ s.e.m) and subject compliance was assessed from 3-day food records, which included two weekend days and one weekday, at the start and

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end of each investigation period. Diet records were reviewed with each subject. Adequate compliance is assumed when subjects report consuming the designated breakfast. Energy and macronutrient intakes from the subjects’ combined food records were calculated using Food Works (Version 3 Xyris Software, 2002) based on data from the AUSNUT database.

Measurement of Satiety Satiety effects of the breakfast meals were assessed on the occasions on which 3-day food diaries were recorded by a questionnaire [15] with a rating from 1 to 10 being given to the level of satiety felt right after breakfast, just before lunch and before dinner where 1 ⫽ Hungry; starving, dizzy, irritable, 5 ⫽ Neutral; comfortable, neither hungry nor full, 10 ⫽ Satiety; full to the point of feeling satified. The questionnaires were completed on the occasions food records were taken.

Biochemical Analyses Serum and plasma was isolated by low-speed centrifugation at 3000rpm for 10 minutes (Rofina 48R centrifuge). Samples were stored at ⫺80°C until ready to be analysed. The blood glucose was measured in plasma using an enzymatic assay kit (Randox Laboratories, UK). Serum total cholesterol and triglyceride were analysed using enzymatic colorimetric kits (Thermo Trace Ltd, Melbourne, Australia). Serum HDL-cholesterol concentration was measured after separating out the LDL and VLDL lipoproteins by selective precipitation, the supernatant containing HDL cholesterol was analysed using enzymatic colorimetry kit (Thermo Trace Ltd, Melbourne, Australia). LDL-cholesterol was calculated using the Friedwalde equation [16]. Plasma insulin was measured by enzyme-linked immunosorbent assay (ELISA) based on two Table 3. Macronutrient Composition of High GI and Low GI Breakfast Replacement Meals

Energy (KJ) Protein (g) Fat (g) Carbohydrate (g) Fibre (g) Glycemic load (GI) Glycemic index (GL)

Low GI breakfast

High GI breakfast

1081 10.0 4.8 40.7 9.92 1455 35

1065 9.3 4.5 43.0 3.18 2960 79

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Effect of a Low Glycaemic Index Breakfast Table 4. The Macronutrient Composition of Intervention Diets before and after 3 Weeks of Low GI or High GI Diets Derived from 3-Day Food Records1 Low

High P-value2

Variable Energy (Kj) Protein (g) Fat (g) Carbohydrate (g) Fibre (g) 1 2

Before

Final

Before

Final

9010 ⫾ 600 83.1 ⫾ 5.18 76.1 ⫾ 8.77 244 ⫾ 26.2 20.2 ⫾ 2.05

7600 ⫾ 494 74.4 ⫾ 3.64 60.9 ⫾ 4.33 218 ⫾ 16.4 22.03 ⫾ 2.32

8125 ⫾ 634 83.5 ⫾ 5.23 75.3 ⫾ 7.44 237 ⫾ 21.1 21.4 ⫾ 1.96

7350 ⫾ 434 80.2 ⫾ 4.07 63.23 ⫾ 5.07 211 ⫾ 15.2 19.36 ⫾ 2.96

0.45 0.306 0.562 0.812 0.630

Data is represented as means ⫾ s.e.m. Data was analysed using repeated measures analysis of variance taking into account the repeated measurements for each subject.

monoclonal antibodies (Dako Diagnostic, UK) according to manufacturer’s instructions. The homeostasis model assessment (HOMA score) was used as a surrogate estimate of the state of insulin sensitivity by multiplying fasting insulin concentration (mIU/L) with fasting glucose concentration (mM) and dividing by 22.5.

Statistical Analysis This is a cross over study where power calculation is based on a predicted change in fasting triglyceride of 20% difference between groups over the treatment period. Assuming a standard deviation of 15%, a sample size of 8 subjects/group provided sufficient power (90%) to detect a significance level of p ⬍ 0.05 in a paired student t-test calculation. A total of 21 subjects were recruited to ensure adequate numbers in the event of subjects choosing to withdraw from the trial. Data is expressed as mean ⫾ SEM. Changes in all measurements (ie lipids, insulin, glucose, weight etc) during each dietary period (baseline versus final data) were compared (Low GI versus High GI). The 2 groups were compared using repeated measures analysis of variance taking into account the repeated measurements for each subject. Results were considered significant when P values ⬍0.05. Covariates used were age, weight, diet order and baseline lipid and glucose values, as well as energy in each diet phase. Statistical analysis was performed with SPSS for windows statistical software version 11.0 (Chicago, USA).

RESULTS Diets and Saiety The changes in dietary composition as assessed from 3-day food records are as shown in Table 4. Results showed that total daily energy intake (calculated from 3-day dietary records) were not significantly different between the low and high dietary interventions after 21 days (final: 7600 ⫾ 494 versus 7350 ⫾ 434, respectively). Although low GI intervention resulted in lower absolute intake (g) of all macronutrients measured compared with high GI intervention, the differences between interventions did not reach statistical significance. Total compliance with the prescribed diets (ie completion of assigned breakfast items) was observed in all subjects. A change in satiety within each diet treatment was assessed (Table 5). The change in satiety after the consumption of the breakfast meal and also in the period before lunch (baseline versus final data) during the Low GI intervention was higher (p ⬍ 0.05) than that during the High GI period (Table 5). Satiety ratings were observed to be 7% and 12% higher after breakfast and lunch, respectively when subjects consumed a low GI breakfast compared with a high GI breakfast.

Body Weight and Metabolic Factors Body weight (84.34 ⫾ 4.88 kg versus 84.25 ⫾ 4.43 kg, respectively) and other anthropometric measures such as waist (101.17 ⫾ 6.23 cm versus 102.22 ⫾ 2.68 cm, respectively), %

Table 5. Comparison of Satiety Ratings before and after 3 Weeks of Low GI or High GI Diets1 Low

High P-value2

After breakfast Before lunch Before Dinner

Before

Final

Before

Final

3.68 ⫾ 0.23 4.08 ⫾ 0.17 3.59 ⫾ 0.29

3.95 ⫾ 0.14 4.85 ⫾ 0.23 4.4 ⫾ 0.205

4.17 ⫾ 0.21 4.12 ⫾ 0.23 3.94 ⫾ 0.2

3.68 ⫾ 0.17 3.59 ⫾ 0.17 3.66 ⫾ 0.175

0.014* 0.034* 0.857

Data are given as means ⫾ s.e.m of satiety ratings. Data was analysed using repeated measures analysis of variance. Changes during each dietary period (baseline versus final data) were compared (Low GI versus High GI). P values ⬍ 0.05 were considered statistically significant (*P ⬍ 0.05).

1 2

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Effect of a Low Glycaemic Index Breakfast Table 6. Comparison of Anthropometric Data before and after 3 Weeks of Low GI or High GI Diets1 Low

High P-value2

Weight (kg) Waist (cm) Hip (cm) Body Fat (%) BMI (kg/m2) 1 2

Before

Final

Before

Final

84.05 ⫾ 4.85 100.02 ⫾ 6.56 111.28 ⫾ 5.63 40.44 ⫾ 2.69 32.8 ⫾ 0.95

84.34 ⫾ 4.88 101.17 ⫾ 6.23 110.20 ⫾ 5.58 39.65 ⫾ 2.70 32.8 ⫾ 0.94

85.34 ⫾ 420 101.25 ⫾ 2.57 111.49 ⫾ 448 40.35 ⫾ 1.19 30.5 ⫾ 0.22

84.25 ⫾ 4.43 102.22 ⫾ 2.68 111.36 ⫾ 4.69 40.21 ⫾ 2.15 30.7 ⫾ 0.21

0.614 0.221 0.547 0.959 0.632

Data are given as means ⫾ s.e.m. Data was analysed using repeated measures analysis of variance.

body fat (39.65 ⫾ 2.70 versus 40.21 ⫾ 2.15, respectively) and hip (110.20 ⫾ 5.58 cm versus 111.36 ⫾ 4.69 cm, respectively) were comparable at the end of the low and high GI intervention (Table 6). In addition, fasting triacyglycerol, insulin and total, HDL and LDL cholesterol levels were unaffected by the shortterm changes in the type of breakfast (Table 7). However, fasting glucose levels (Fig. 1) were lower when subjects were consuming a low GI (4.88 ⫾ 0.11 mmol/L) breakfast for 3 weeks (final) compared to when they were consuming a high GI breakfast (5.11 ⫾ 0.14 mmol/L) (p ⬍ 0.05). There were no differences in changes in systolic or diastolic blood pressure observed between the dietary periods (Table 7).

seen with a single meal GI modification suggest that this could potentially be a good public health recommendation, as opposed to total dietary GI modification of all meals during the day. In this study, satiety was measured after breakfast, before lunch and before dinner using a self-administered questionnaire. Results demonstrated that satiety was higher after breakfast and before lunch, but not before dinner. These results are consistent with a postprandial study by van Amelsvoort JM and Weststrate JA in 1992 [20], which found that low GI food induced satiety for up to 6 hours after meal. In a recent review by Ludwig DS (2000) [21], 15 out of the 16 studies reviewed have shown that lower GI foods leads to decreased hunger, increased satiety or decreased energy intake. According to the glucostatic hypothesis, a rapid increase in blood glucose after the consumption of high GI foods is associated with decreased satiety but a gradual, prolonged elevation of blood glucose leads as seen to sustained satiety [13,22]. In addition, other factors such as prolonged contact of food with the gastrointestinal tract with slowly digested low GI foods may also play a role in initiating and sustaining satiety through the secretion of various satiety peptides [13]. Although we observed a significant increase in satiety, this study failed to find a significant decrease in voluntary energy intake. The reason that a decrease in energy intake was not observed may have been because the change in satiety may not have been clinically significant. The lack of significance may also be due to large variations in energy intake derived

DISCUSSION The current study was designed to evaluate the short-term dietary effects of GI modification on glycemic control, lipid metabolism, anthropometric measures, satiety and blood pressure. To our knowledge, this is the first study to determine the effects of a single meal substitution in non-diabetic, obese or overweight subjects. Previous studies have shown beneficial effects with single meal interventions in diabetic subjects [17– 19], but it is unclear if similar benefits would be seen in non-diabetic subjects, overweight or obese subjects. The present study showed that substituting a high GI breakfast with a low GI breakfast resulted in decreases in fasting blood glucose level in obese, non-diabetic subjects. Such positive effects

Table 7. Fasting Plasma Lipid and Blood Pressure Levels before and after 3 Weeks of Low GI or High GI Diets1 Low

High P-value2

Total cholesterol (mmol/L) HDL-cholesterol (mmol/L) LDL-cholesterol (mmol/L) Triacylglyceride (mmol/L) Fasting insulin (␮IU/ml) HOMA score Systolic blood pressure (mmHg) Diastolic blood pressure (mmHg) 1 2

Before

Final

Before

Final

6.33 ⫾ 0.28 1.98 ⫾ 0.14 2.91 ⫾ 0.21 1.55 ⫾ 0.21 5.45 ⫾ 0.80 1.23 ⫾ 0.22 132.36 ⫾ 3.32 85.27 ⫾ 3.23

6.27 ⫾ 0.23 1.93 ⫾ 0.14 2.95 ⫾ 0.22 1.54 ⫾ 0.13 5.22 ⫾ 0.80 1.13 ⫾ 0.35 128.98 ⫾ 3.53 87.54 ⫾ 3.33

6.35 ⫾ 0.4 1.97 ⫾ 0.18 3.05 ⫾ 0.31 1.53 ⫾ 0.15 5.38 ⫾ 0.93 1.22 ⫾ 0.26 130.34 ⫾ 2.68 86.73 ⫾ 2.98

6.39 ⫾ 0.33 1.99 ⫾ 0.17 2.98 ⫾ 0.35 1.56 ⫾ 0.19 5.45 ⫾ 0.80 1.23 ⫾ 0.34 130.23 ⫾ 2.97 88.24 ⫾ 3.74

0.495 0.582 0.78 0.178 0.228 0.124 0.734 0.424

Data are given as means ⫾ s.e.m. Data was analysed using repeated measures analysis of variance.

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Effect of a Low Glycaemic Index Breakfast

Fig. 1. Fasting glucose concentrations before and final measurements with low GI or high GI diets. Fasting glucose concentrations before and final measurements with low GI or high GI diets for 3 weeks. Data are given as means ⫾ s.e.m. Data was analysed using repeated measures analysis of variance taking into account the repeated measurements for each subject. Statistically significant differences from between groups is indicated by *p ⬍ 0.05.

from self-reported food records or errors in satiety records. Previous intervention studies investigating the effect of GI on satiety were performed in laboratory settings involving precise measurements of food consumed [22–24]. The inaccuracies in food records in this study when compared to weighed food intake may have masked an existing significant difference in energy intake in this study, or there may not have been any real decrease in energy intake as there was no weight loss at the end of the intervention. The current study found that subjects had a lower fasting blood glucose after 3 weeks of low GI breakfast as compared to those on high GI breakfast. An increased fasting blood glucose, or impaired fasting glucose is one of the risk markers for development of diabetes and cardiovascular diseases [25]. Therefore, a decrease in fasting glucose is beneficial in preventing the development of metabolic diseases, especially in high risk groups as represented in this study. Previous studies have shown that low dietary GI decreases fasting blood glucose in diabetic subjects [6,26,27]. We observed similar effects in non-diabetic, overweight or obese subjects with a single meal GI modification. The decrease in fasting blood glucose may be due to a slight improvement (not significant) in insulin sensitivity (Table 7) when subjects consumed a low GI breakfast compared with a high GI breakfast for 3 weeks (1.13 ⫾ 0.35 vs 1.23 ⫾ 0.34, respectively). It has also been previously been shown that insulin sensitivity improved in women after 3 weeks of low GI intervention, an effect attributed to the increased insulin-stimulated glucose uptake by adipocytes [28]. Subjects who participated in our study were classified as either overweight and obese with waist measurements (100 cm) and average BMI of 31, were insulin sensitive (HOMA score less than 2). Since these subjects had normal insulin sensitivity at the beginning of the study, it may be the reason why it did not change significantly after the 21 days intervention with a low GI breakfast.

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Consistent with another short-term study by Bouche et al (2002) [12] that involved a 5 weeks intervention, we did not observe any significant effects in other lipid parameters within 3 weeks. In contrast, reduced triglycerides, total-cholesterol, and LDL-cholesterol but with no effect on HDL-cholesterol was reported in a medium-term study, which involved daily consumption of low GI meals for 3 months [7]. These results suggest that changes in fasting cholesterol concentrations resulting from GI modification may require a longer timeframe than the duration of this study. This study did not find any changes in body weight or any anthropometric measures. In recent review [29], the findings of 15 parallel and crossover studies reported that GI had no effects on body weight. This is not surprising, however, as all studies reviewed were designed to deliver similar energy values for both low GI and high GI meals. One of the ways low GI foods could lead to weight loss is by decreasing energy intake through increased satiety. Therefore, ad libitum studies instead of energy-controlled studies are required to determine the effect of GI on body weight. In terms of anthropometric measures, Bouche et al (2002) [12] had observed a decrease in fat mass and an increase in lean body mass after 5 weeks of low GI diet in overweight non-diabetic men despite no significant change in body weight. Our study did not find similar changes, probably due to a shorter intervention duration or a single meal instead total dietary GI modification compared to the previous study. In conclusion, this study found that modifying GI in a single meal (ie at breakfast) alone resulted in lower fasting blood glucose levels and induced satiety until lunch. A high compliance rate also confirmed the fact that such modification is highly achievable. Together, these findings suggest that breakfast modification could potentially be a useful public health recommendation. However, it needs to be stressed that the small size of study group is an important limitation of this study therefore future studies should be conducted with larger sample sizes and for a longer time period to investigate the long-term benefits of breakfast meal modification on glycemic control, insulin sensitivity, blood pressure, body weight and anthropometric measures.

ACKNOWLEDGEMENTS The project was supported by grants from the Curtin Developmental Research Grant (DRG) Scheme.

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Received September 15, 2006; revision accepted October 12, 2007.

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