Carbohydrate intake before physical activity

Athletes are cautioned against consuming large amounts of carbohydrates before exercise. This caution is based on the results of a study by Foster et al. that showed that consuming 75 g of glucose 30 min before exercise reduced endurance performance due to accelerated muscle glycogen depletion and hypoglycemia. High blood insulin levels caused by pre-exercise carbohydrate consumption were implicated in these effects.

As a result of this research, some practitioners have advised athletes to avoid carbohydrates before exercise or to use low-glycemic index foods. This advice is based on the fact that low-glycemic index foods (beans, milk) provide a slow but continuous release of glucose into the blood, without an accompanying surge in insulin. In comparison, sugar and high-glycemic index foods (bread, potatoes, sports drinks, and many breakfast cereals) quickly increase blood glucose and insulin levels.

Research by Hargreaves et al. contradicts earlier studies by Foster. Subjects consumed 75 g of glucose (high glycemic index), 75 g of fructose (low glycemic index), or water 45 min before cycling to failure. Although glucose consumption resulted in high blood insulin levels and low blood glucose levels, there was no difference in time to failure between cyclists who consumed glucose, fructose, or water.

Consuming high-glycemic index carbohydrates 1 h before exercise, especially in the fasted state, may improve performance. Sherman et al. compared the consumption of drinks containing 1.1 g-kg and 2.2 g-kg carbohydrate 1 h before exercise. Cyclists rode at 70% V02max for 90 min. Early serum insulin levels increased at the onset and during exercise, and blood glucose levels initially decreased. However, performance was enhanced by 12.5% due to carbohydrate consumption, primarily through increased oxidation.

Hyperglycemia and hyperinsulinemia resulting from pre-exercise carbohydrate ingestion are transient and will likely not affect performance unless the athlete is sensitive to the drop in blood glucose and experiences premature muscle fatigue or CNS symptoms indicative of hypoglycemia. Athletes should evaluate their responses to both low- and high-glycemic index high-carbohydrate meals to determine which is best.

Low glycemic index carbohydrates may be an option for athletes who are sensitive to drops in blood glucose. Thomas et al. compared the carbohydrate intake of lentils (low glycemic index) and water 1 h before exercise. Cyclists rode to exhaustion at 65-70% V02max. Lentils provided a gradual rise and fall in blood glucose compared with potato, glucose, and water. The endurance period provided by lentils (low glycemic index) was 20 min longer than the other conditions, which were not different from each other.

Athletes who are sensitive to low blood glucose levels have several strategies to choose from.

• Take low glycemic index carbohydrates before exercise.
• Take carbohydrates a few minutes before exercise.
• Take carbohydrates during exercise.

Consuming high glycemic index carbohydrates (such as glucose) immediately before anaerobic exercise (sprinting or weightlifting) does not improve performance. Sufficient ATP, creatine phosphate (CrP), and muscle glycogen have been stored for these anaerobic exercises. High glycemic index carbohydrates do not provide rapid energy release, allowing athletes to train harder. Consuming excessive amounts of carbohydrates before exercise may increase the risk of gastrointestinal upset such as cramps, diarrhea, and bloating.

Pre-workout meal

Athletes are advised to eat 2-3 hours before exercise to allow time for the stomach to empty. This is based on the fact that if food remains in the stomach, the athlete may feel nausea or discomfort at the start of exercise as blood is diverted from the gastrointestinal tract to the working muscles, so many athletes who train or compete in the morning fast rather than rise at dawn for breakfast. Such fasting depletes liver glycogen stores and may impair exercise performance, especially if the athlete is subjected to prolonged strenuous exercise that requires blood glucose levels to be maintained.

During exercise, athletes rely primarily on existing glycogen and fat stores. Although eating before exercise does not provide immediate energy, it can provide energy when an athlete is working hard for 1 hour or more. Eating also prevents hunger, which in itself can impair performance. Having carbohydrates in the meal increases blood glucose levels to provide energy to the working muscles.

Consuming carbohydrates 2-4 hours before morning exercise helps restore liver glycogen stores. This allows for exercise that is largely fueled by blood glucose. If muscle glycogen levels are also low, consuming carbohydrates a few hours before exercise increases them. If delayed gastric emptying is a concern, liquid foods should be consumed.

Sherman et al. evaluated the effects of 312-, 156-, and 45-g liquid carbohydrate meals 4 h before exercise. The high-glycemic index carbohydrate meals provided 4.5, 2, and 0.6 g-kg carbohydrate, respectively. A 95-min interval cycling session was performed, followed by testing after a 5-min rest. The 312-g carbohydrate meal improved performance by 15% despite elevated insulin levels at the onset of exercise.

Nuefer et al. also found that endurance was enhanced by consuming a mixed meal (porridge, bread, milk, fruit juice) containing 200 g of carbohydrates 4 h before exercise.

Carbohydrate-rich, palatable, and well-tolerated foods are ideal for pre-exercise consumption. Sherman et al. suggest that a pre-exercise meal containing 1.0–4.5 g-kg of carbohydrate should be consumed 1–4 h before exercise. To avoid potential gastrointestinal upset, the carbohydrate and calorie content should be decreased as the interval between meals and exercise decreases. For example, a 1 g-kg serving of carbohydrate should be consumed 1 h before exercise, and a 4.5 g-kg serving 4 h before exercise.

Liquid food

The industry has created several types of liquid food specifically for athletes - GatorPro, Nutrament and Exceed Nutritional Beverage.

These foods meet the nutritional needs before exercise: they are rich in carbohydrates, taste good, and provide the body with energy and fluid. Liquid food, unlike regular food, should be consumed immediately before competition, as it helps to empty the stomach quickly. This will help athletes who are under stress avoid nausea.

Liquid food produces scanty stools, which minimizes the weight gain immediately after eating. This is especially beneficial for wrestlers who must "maintain weight." Liquid food is also convenient for athletes participating in all-day competitions, tournaments, and multi-event events (such as triathlon).

Liquid food can also be used as a nutritional supplement during intense training sessions when caloric needs are extremely high. It provides a significant amount of calories and promotes satiety.

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