| The aims of this thesis were to, first, determine the glycemic index (GI) of traditional Chinese foods, and second, to investigate the effect of GI and fructose content in pre-exercise mixed meals on substrate utilization during subsequent brisk walking.;Study I (Chapter 4) determined the GI values of 29 traditional Chinese foods. Fifteen healthy adults (eight males and seven females; mean +/- SEM: age, 25.4+/-1.2 year; BMI, 21.2+/-0.6 kg·m-2 ) volunteered to participate in the study. All subjects consumed either 50 g of glucose or one of 29 test foods containing 50 g of available carbohydrate (CHO) after 10--14 hrs overnight fast. Capillary blood glucose concentrations were analyzed immediately before food consumption and 15, 30, 45, 60, 90, and 120 min after consumption. The GI value of each test food was calculated by expressing the incremental area under the blood response curve (IAUC) value of glucose for the test food as a percentage of each subject's average IAUC value for the glucose. Among the 29 test foods, seven were classified as low-GI foods (i.e., Tuna Fish Bun, Egg Tart, Green Bean Dessert, Chinese Herbal Jelly, Fried Rice Vermicelli in Singapore-style, Udon Noodle, and Spring Roll), 13 as moderate-GI foods (i.e., Baked Barbecued Pork Puff, Fried Fritter, "Mai-Lai" Cake, "Pineapple" Bun, Fried Rice Noodles with Sliced Beef, Barbecue Pork Bun, Moon Cakes, Glutinous Rice Ball, Instant Sweet Milley Bun, Shanghai Noodle, Rice Vermicelli, Instant Noodle, and Salted Meat Rice Dumpling), and the remaining nine as high-GI foods (i.e., Fried Rice in Yangzhou-Style, Sticky Rice Wrapped in Lotus Leaf, Steamed Glutinous Rice Roll, Jam and Peanut Butter Toast, Plain Steamed Vermicelli Roll, Red Bean Dessert, Frozen Sweet Milky Bun, Shrimp Egg Noodle, and Spinach Noodle). The results of this study provided valuable information to both researchers and the general public on their food preference. A number of the food items in the present study were used in subsequent works, namely, Study II and Study III.;Study II (Chapter 5) investigated the effect of GI and fructose content in breakfast on substrate utilization during subsequent brisk walking. Ten healthy young males (mean +/- SEM: age, 21.7+/-1.5 year; BMI, 20.9+/-1.1 kg·m-2; VO2max, 53.7+/-3.7 mL·kg-1 ˙min-1) volunteered to participate in the study. All subjects completed 60-min of 46% VO2max brisk walking 2-hrs after consuming one of three breakfast meals: a low-GI meal without fructose (LGI), a low-GI meal including fructose beverage (LGIF) and a high-GI meal (HGI). The three main trials were completed in a counterbalanced crossover design. Calculated GI values for LGI, LGIF, and HGI breakfast meals were 41, 39, and 72, respectively. These three isocaloric breakfast meals provided 1.0 g·kg-1 body weight CHO for each subject and approximately 20% energy from fat, 17% from protein, and 63% from CHO. In the LGIF and HGI trials, approximately 25% of energy came from either fructose or glucose beverage. Substrate utilization was measured using indirect respiratory calorimetry method. Capillary blood samples and venous blood samples were collected at certain time points during the experiment. During the postprandial period, IAUC values of glucose and insulin were higher (p<0.05) in the HGI trial, compared with those in the LGI and LGIF trials (HGI vs. LGI and LGIF: glucose, 223.6+/-19.1 vs. 70.2+/-7.4 and 114.1+/-16.4 mmol·min·L-1; insulin, 4257+/-932 vs. 920+/-319 and 1487+/-348 mU·min·L-1). During brisk walking, no difference was observed in substrate utilization between LGIF and HGI trials. Nevertheless, decreased CHO oxidation and increased fat oxidation were found (p<0.05) in the LGI trial when compared with the other two trials (LGI vs. LGIF and HGI: CHO, 59.3+/-2.4 vs. 69.8+/-3.9 and 72.7+/-3.9 g; fat, 22.7+/-2.0 vs. 18.5+/-1.7 and 17.6+/-1.3 g). In conclusion, compared with LGI breakfast meal without fructose, either HGI breakfast meal or the presence of fructose in a similar LGI breakfast meal decreased fat oxidation and increased CHO oxidation during subsequent brisk walking. Therefore, it appeared that both GI and fructose content in a breakfast individually affected substrate utilization during subsequent moderate intensity exercise.;Study III (Chapter 6) investigated the effect of GI and fructose content in lunch meal on substrate utilization during subsequent brisk walking. Ten healthy young male adults (mean +/- SEM: age, 20.5+/-1.0 year; BMI, 20.8+/-0.7 kg·m-2; VO2max, 48.6+/-1.9 mL·kg-1·min-1) were recruited to participate in the study. All subjects were required to complete three main trials in a counterbalanced crossover design. The subjects completed 60-min of brisk walking at approximately 50% of individual VO2max after consuming a standard breakfast meal and one of three lunch meals, i.e., a low-GI meal without fructose (LGI), a low-GI meal including fructose beverage (LGIF), or a high-GI meal (HGI). Calculated GI values for LGI, LGIF, and HGI lunch meals were 41, 39, and 72, respectively. All lunch meals provided 1.0 g·kg-1 body weight CHO for each subject and approximately 20% energy from fat, 17% from protein, and 63% from CHO. In the LGIF and HGI trials, approximately 25% of energy came from either fructose or glucose beverage. Substrate utilization was measured using indirect respiratory calorimetry method. Capillary blood samples and venous blood samples were collected at certain time points during the experiment. During the postprandial period after lunch, IAUC values of glucose and insulin were higher (p<0.05) in the HGI trial, compared with those in the LGI and LGIF trials (HGI vs. LGI and LGIF: glucose, 223.5+/-24.4 vs. 92.5+/-10.4 and 128.0+/-17.7 mmol·min·L-1; insulin, 3603+/-593 vs. 1425+/-289 and 1888+/-114 mU·min·L-1). During brisk walking, decreased CHO oxidation was found (p<0.05) in the LGI trial when compared with the LGIF and HGI trials, whereas no difference was found between the latter two trials (LGI vs. LGIF and HGI: 60.8+/-4.0 vs. 68.1+/-6.0 and 74.4+/-4.7 g). No difference was observed in fat oxidation among the three trials (LGI vs. LGIF vs. HGI: 21.6+/-2.3 vs. 19.2+/-2.3 vs. 16.4+/-2.2 g). In conclusion, compared with a LGI lunch meal without fructose, either a HGI lunch meal or the presence of fructose in a LGI lunch meal induced more CHO oxidation during subsequent brisk walking. However, no differences were found in fat oxidation among the three trials, although there was a trend to be higher in the LGI trial than in the LGIF and HGI trials. Consumption of a standard breakfast appeared to reduce the effect of pre-exercise lunch meals with different GI and fructose content on substrate utilization during subsequent moderate intensity exercise to a certain degree.;According to the results of the studies conducted in this thesis, both GI and fructose content of pre-exercise mixed meals could individually affect substrate utilization during subsequent moderate intensity exercise. Furthermore, a slight difference was observed in this effect when meals were consumed after a standard breakfast and 4-hrs of fasting compared with when these were consumed after an overnight fast. The findings of this thesis enhance the understanding of the effect of pre-exercise CHO consumption on substrate utilization during subsequent moderate intensity exercise. The results likewise provide practical information for those who exercise for health or weight management. |
