Liquid meals produce a low stool residue, thereby minimizing immediate weight gain. This is espe-


cially advantageous for athletes who need to “make weight.” Liquid meals are convenient for athletes competing in day-long tournaments, meets, and ultraendurance events (eg, Ironman Triathlon). Liquid meals can also be used for nutritional supplementation during heavy training when energy require- ments are extremely elevated.


Carbohydrate in the Hour Before Exercise


Based primarily on the results of only one early study, athletes have been cautioned to avoid eating carbo- hydrate in the hour before exercise. In the late 1970s, researchers found that consuming 75 g of glucose 30 minutes before cycling at 80% of VO2


exercise time by 19%. High blood insulin levels induced by preexercise carbohydrate feeding were blamed for this chain of events.32


max caused initial rapid decrease in blood glucose and reduced However, subsequent studies have contradicted these findings. Preexercise carbo-


hydrate feedings either improve performance or have no detrimental effect. In most cases, the decrease in blood glucose observed during the first 20 minutes of exercise is self-correcting and has no apparent effects on the athlete.13,30,33 A small number of athletes react negatively to carbohydrate feedings in the hour before exercise and


experience symptoms of hypoglycemia and fatigue. Te reason for this unusual reaction is not known. Pre- ventive strategies include the following34


:


1. Choose low-GI carbohydrate sources before exercise because they produce more stable glucose and insulin responses.


2. Consume carbohydrate a few minutes before exercise. 3. Wait until exercising to consume carbohydrate. Te metabolic and performance effects of ingesting carbohydrate shortly before exercise are similar to


consuming carbohydrate during exercise. Te exercise-induced increase in the hormones epinephrine, norepinephrine, and growth hormone inhibit the release of insulin and thus counter insulin’s effect in reducing blood glucose.34


Preexercise Carbohydrate and the Glycemic Index A 1991 study sparked interest in the use of the GI in sports.35


kilogram from lentils (low GI) 1 hour before cycling at 67% of VO2


Consumption of 1 g carbohydrate per max promoted more stable blood


glucose levels during exercise and increased endurance performance compared with an equal amount of carbohydrate from potatoes (high GI). Few studies have reported enhanced endurance from consum- ing low GI meals before exercise, although most studies have failed to show improvements in exercise performance.4,13,36 Te overall importance of the preexercise meal for maintaining carbohydrate availability is questionable


because endurance athletes also consume carbohydrate-rich foods and fluids during prolonged exercise.4 When carbohydrate is ingested during exercise, according to sports nutrition guidelines, there is no dif- ference in performance or carbohydrate oxidation between low- and high-GI preexercise meals. Tus, consuming carbohydrate during exercise negates the glycemic effects of the preexercise meal on performance and metabolism.13,36-38 A low-GI preexercise meal may be beneficial when it is difficult to consume carbohydrate during pro-


longed exercise or when the athlete reacts negatively to carbohydrate feedings. However, there is no evidence that athletes will universally benefit from low-GI preexercise meals, especially when athletes can refuel during exercise. Te type, timing, and amount of carbohydrate in the preexercise meal should be individualized based on the athlete’s specific event, gut comfort, and individual preferences.4,13 Consuming a high-GI carbohydrate (eg, glucose) immediately before anaerobic exercise, such as sprint-


ing or weight liſting, will not provide athletes with a quick burst of energy, allowing them to exercise harder. Tere is adequate ATP, creatine phosphate, and muscle glycogen already stored for these anaerobic tasks.


28 SECTION 1: SPORTS NUTRITION BASICS


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