510 International Journal of Sport Nutrition and Exercise Metabolism, 2006, 16, 510-527 © 2006 Human Kinetics, Inc. A Low Glycemic Index Meal Before Exercise Improves Endurance Running Capacity in Men Ching-Lin Wu and Clyde Williams This study investigated the effects of ingesting a low (LGI) or high (HGI) glyce- mic index carbohydrate (CHO) meal 3 h prior to exercise on endurance running capacity. Eight male recreational runners undertook two trials (LGI or HGI) which were randomized and separated by 7 d. After an overnight fast (12 h) the subjects ingested either a LGI or HGI meal 3 h prior to running at 70% VO 2max until exhaustion. The meals contained 2 g/kg body mass CHO and were isocaloric and iso-macronutrient with calculated GI values 77 and 37 for the HGI and LGI respectively. The run times for the LGI and HGI trials were 108.8 ± 4.1 min and 101.4 ± 5.2 min respectively (P = 0.038). Fat oxidation rates were higher during exercise after the LGI meal than after the HGI meal (P < 0.05). In summary, inges- tion of a LGI meal 3 h before exercise resulted in a greater endurance capacity than after the ingestion of a HGI meal. Key Words: carbohydrates, glycemic index, fatigue, insulinemia Ingestion of carbohydrate (CHO) before exercise may result in an improved exercise performance when compared with exercise in the fasting state (3, 4, 15, 22, 24, 35). Paradoxically, ingesting CHO before exercise increases the rate utilization of this limited substrate store and yet still delays the onset of fatigue. This increased rate of CHO utilization is a consequence of a glucose-induced rise in plasma insulin concentration that, in turn, suppresses the rate of fatty acid oxidation (6, 16). Strategies that help increase the contribution of fat metabolism to energy pro- duction during prolonged exercise will lead to a more economical use of the body’s limited CHO stores and consequently, an increase in endurance capacity. One such strategy is to use low glycemic index (LGI) carbohydrate foods in pre-exercise meals (2). Consuming LGI CHO foods results in lower glucose and insulin concentrations than after consuming high GI (HGI) CHO foods (17). Several studies have exam- ined the effects of ingesting foods with different GI values on subsequent exercise performance (8, 11, 18-20, 25, 26, 28-30, 34) however only some have reported improvements in exercise performance (8, 18, 19, 20, 28, 34). The inconsistency Wu is with the Dept of Exercise Health Science, National Taiwan College of Physical Education, Taiwan. Williams is with the School of Sport and Exercise Sciences, Loughborough University, Loughborough, UK.