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The aim of this review is to provide an up-to-date summary of the evidence surrounding glycemic index (GI) and endurance performance. Athletes are commonly instructed to consume low-GI (LGI) carbohydrate (CHO) before exercise, but this recommendation appears to be based on the results of only a few studies, whereas others have found that the GI of CHO ingested before exercise has no impact on performance. Only 1 study was designed to directly investigate the impact of the GI of CHO ingested during exercise on endurance performance. Although the results indicate that GI is not as important as consuming CHO itself, more research in this area is clearly needed. Initial research investigating the impact of GI on postexercise recovery indicated consuming high-GI (HGI) CHO increased muscle glycogen resynthesis. However, recent studies indicate an interaction between LGI CHO and fat oxidation, which may play a role in enhancing performance in subsequent exercise. Despite the fact that the relationship between GI and sporting performance has been a topic of research for more than 15 yr, there is no consensus on whether consuming CHO of differing GI improves endurance performance. Until further well-designed research is carried out, athletes are encouraged to follow standard recommendations for CHO consumption and let practical issues and individual experience dictate the use of HGI or LGI meals and supplements before, during, and after exercise.
Preexercise Nutrition and GI
Most studies suggest that consuming LGI CHO before exercise results in a favorable metabolic profile during exercise, but only some report an enhancement in performance. Taken together the studies suggest there may be benefits to consuming LGI CHO before exercise, but to date, no research has indicated that consuming HGI foods before exercise negatively affects endurance performance. Recent improvements in study design to include mixed meals and CHO ingestion both before and during exercise mean that researchers are getting closer to being able to mimic real-life sporting situations. However, until methodology is developed that allows for identification of the cause of the disparity between physiology and performance, it is unlikely that a definite answer will be reached. Until that time, athletes are encouraged to follow standard recommendations in terms of the timing and amount of CHO ingested before exercise and to let practical issues and individual experience dictate their use of HGI or LGI meals before exercise.
Nutrition During Exercise and GI
Consumption of CHO during exercise is common practice among athletes. Intuitively, many athletes opt to consume HGI CHO during exercise, possibly because most HGI foods are less bulky and easier to consume. However, research into the effect of GI of CHO consumed during exercise is severely lacking. The one study that investigated the consumption of CHOs of differing GIs during exercise reported that the consumption of CHO itself was more important than the GI of the CHO consumed. However, this result is far from conclusive. Athletes are encouraged to let individual preference guide their
selection of CHO while giving consideration to the type of training or competition and the length and intensity of each exercise session.
Postexercise Nutrition and GI
Initial research suggested that consuming HGI CHO during recovery increased muscle glycogen synthesis postexercise. This may be particularly important to athletes who train twice a day and thus have limited recovery time between sessions. However, when recovery periods are longer, protein (which is commonly found in commercially available LGI foods and beverages) may be included without any negative impact on glycogen resynthesis and benefits in terms of muscle protein synthesis. Recent results suggest that the interaction between increased fat oxidation and LGI CHO consumed in the first 24 hr of recovery may play an important role in enhancing subsequent performance. However, these studies are yet to be replicated in fed participants.
Between individuals of equal athletic ability, nutrition may be the key factor in success. Optimizing dietary strategies before, during, and after exercise may provide endurance athletes with the winning advantage. However, the role GI plays in the complex area of enduranceperformance enhancement is inconclusive. Future research should consider the training regimens of athletes because the type of training and competition being performed often dictates dietary strategies. Acute laboratory studies investigating the influence of GI on one or two exercise bouts may not truly reflect the influence of a habitual diet of, for example, LGI foods, especially when an athlete is trying to maintain intensity through a period of high-volume training. Thought should also be given to the appropriate use of meals or supplements, in terms of the timing of the feeding in relation to the exercise bout. Future research will need to be carefully designed to consider both individual variability in glycemic response and the importance of using measures of performance that mimic competition as closely as possible. Research should also focus on identifying causes of the currently observed disparities between physiological observations and improvements in performance. Undoubtedly, exciting challenges and opportunities lie ahead for researchers determined to unwind the complexities of GI, nutrition, and endurance performance
FONTE: International Journal of Sport Nutrition and Exercise Metabolism, 2010, 20, 154-165 © 2010 Human Kinetics, Inc.
The aim of this review is to provide an up-to-date summary of the evidence surrounding glycemic index (GI) and endurance performance. Athletes are commonly instructed to consume low-GI (LGI) carbohydrate (CHO) before exercise, but this recommendation appears to be based on the results of only a few studies, whereas others have found that the GI of CHO ingested before exercise has no impact on performance. Only 1 study was designed to directly investigate the impact of the GI of CHO ingested during exercise on endurance performance. Although the results indicate that GI is not as important as consuming CHO itself, more research in this area is clearly needed. Initial research investigating the impact of GI on postexercise recovery indicated consuming high-GI (HGI) CHO increased muscle glycogen resynthesis. However, recent studies indicate an interaction between LGI CHO and fat oxidation, which may play a role in enhancing performance in subsequent exercise. Despite the fact that the relationship between GI and sporting performance has been a topic of research for more than 15 yr, there is no consensus on whether consuming CHO of differing GI improves endurance performance. Until further well-designed research is carried out, athletes are encouraged to follow standard recommendations for CHO consumption and let practical issues and individual experience dictate the use of HGI or LGI meals and supplements before, during, and after exercise.
Preexercise Nutrition and GI
Most studies suggest that consuming LGI CHO before exercise results in a favorable metabolic profile during exercise, but only some report an enhancement in performance. Taken together the studies suggest there may be benefits to consuming LGI CHO before exercise, but to date, no research has indicated that consuming HGI foods before exercise negatively affects endurance performance. Recent improvements in study design to include mixed meals and CHO ingestion both before and during exercise mean that researchers are getting closer to being able to mimic real-life sporting situations. However, until methodology is developed that allows for identification of the cause of the disparity between physiology and performance, it is unlikely that a definite answer will be reached. Until that time, athletes are encouraged to follow standard recommendations in terms of the timing and amount of CHO ingested before exercise and to let practical issues and individual experience dictate their use of HGI or LGI meals before exercise.
Nutrition During Exercise and GI
Consumption of CHO during exercise is common practice among athletes. Intuitively, many athletes opt to consume HGI CHO during exercise, possibly because most HGI foods are less bulky and easier to consume. However, research into the effect of GI of CHO consumed during exercise is severely lacking. The one study that investigated the consumption of CHOs of differing GIs during exercise reported that the consumption of CHO itself was more important than the GI of the CHO consumed. However, this result is far from conclusive. Athletes are encouraged to let individual preference guide their
selection of CHO while giving consideration to the type of training or competition and the length and intensity of each exercise session.
Postexercise Nutrition and GI
Initial research suggested that consuming HGI CHO during recovery increased muscle glycogen synthesis postexercise. This may be particularly important to athletes who train twice a day and thus have limited recovery time between sessions. However, when recovery periods are longer, protein (which is commonly found in commercially available LGI foods and beverages) may be included without any negative impact on glycogen resynthesis and benefits in terms of muscle protein synthesis. Recent results suggest that the interaction between increased fat oxidation and LGI CHO consumed in the first 24 hr of recovery may play an important role in enhancing subsequent performance. However, these studies are yet to be replicated in fed participants.
Between individuals of equal athletic ability, nutrition may be the key factor in success. Optimizing dietary strategies before, during, and after exercise may provide endurance athletes with the winning advantage. However, the role GI plays in the complex area of enduranceperformance enhancement is inconclusive. Future research should consider the training regimens of athletes because the type of training and competition being performed often dictates dietary strategies. Acute laboratory studies investigating the influence of GI on one or two exercise bouts may not truly reflect the influence of a habitual diet of, for example, LGI foods, especially when an athlete is trying to maintain intensity through a period of high-volume training. Thought should also be given to the appropriate use of meals or supplements, in terms of the timing of the feeding in relation to the exercise bout. Future research will need to be carefully designed to consider both individual variability in glycemic response and the importance of using measures of performance that mimic competition as closely as possible. Research should also focus on identifying causes of the currently observed disparities between physiological observations and improvements in performance. Undoubtedly, exciting challenges and opportunities lie ahead for researchers determined to unwind the complexities of GI, nutrition, and endurance performance
FONTE: International Journal of Sport Nutrition and Exercise Metabolism, 2010, 20, 154-165 © 2010 Human Kinetics, Inc.
