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The Glycemic Index and Recovery
By Thomas W. Nesser, PhD, CSCS
The weight loss industry has classified carbohydrates as "good carbs" and "bad carbs". However, when it comes to athletic performance, there are no "bad carbs". All carbohydrates are equally important; the trick is understanding when one carbohydrate is better than another in relation to training.
Even though carbohydrates are the body's primary energy source, they are not the body's only source of energy. The body can also use fats and proteins for energy, though neither are as efficient as carbohydrates. Fats are a rich energy source, however it takes the body more time to breakdown fats to be used as an energy. In addition, the conversion of fat into energy requires a great amount of oxygen. Therefore fats are predominantly used during aerobic (endurance) exercise. While proteins can be used as an energy source, they are not the preferred source because it takes a lot of time for the body to break them down into a useable form. Besides, the protein used as an energy source comes from muscle breakdown. As an athlete, the breakdown of muscle mass is not desired.
When carbohydrates are consumed they are broken down to glucose and released into the blood stream. Carbohydrate sources include grains, fruits, vegetables, and sugar. Glycemic index (GI) is a measure of the rate at which specific carbohydrates are broken down to glucose and released into the blood stream. The ranking used is relative to pure glucose which has a ranking of 100. Carbohydrates with a high GI (e.g. corn flakes = GI value of 80) are rapidly broken down and released into the blood while those with a low GI (e.g. kidney beans = GI value of 29) are slower to break down and released into the blood. See table 1 for a list of carbohydrates and their glycemic score.
Table 1. Glycemic index of Common Foods
Food GI Rank
Peanuts 13
Kidney beans 29
Apple 39
Orange 40
Whole wheat pasta 42
Sweet potatoes 48
Peas 51
Corn 59
Banana 62
Raisins 64
Brown rice 66
White bread 69
White rice 72
Corn flakes 80
Honey 87
Carrots 92
Note: Differences exist in GI ranking due to the exact type of food tested3.
As blood sugar (glucose) levels increase, the pancreas releases insulin to move the glucose from the blood into the tissue where it is used as energy or stored as glycogen. It is important to note insulin also inhibits fat metabolism and protein breakdown. Foods with a high glycemic index are often accompanied by a spike of insulin. The excessive insulin pulls too much glucose from the blood causing fatigue, hunger, and usually additional sugar cravings. This cycle continues throughout the day impeding the use of fats as a fuel and ultimately leading to weight gain. This does not mean all high GI carbohydrates are bad and should be avoided.
High glycemic index foods are very beneficial when consumed prior to, during, and following exercise. During exercise, glycogen is broken down into glucose and released into the blood where it is carried to the working muscles to be used as energy. When an athlete eats a high GI food prior to or during exercise, the absorbed glucose is used as an immediate energy source to fuel the working muscles. Another benefit of consuming carbohydrates during exercise is to spare the use of stored carbohydrate (glycogen), allowing an individual to exercise longer without the risk of depleting glycogen stores.
Following exercise, high glycemic carbohydrates are recommended for quickly replenishing glycogen stores. Upon cessation of exercise there is a 45 minute window in which the body's capacity to replenish glycogen stores is greatest (2). After this optimal window, replenishing glycogen stores will take longer and may not be entirely complete by the next exercise bout which could hinder performance. Not having glycogen stores at full capacity could hinder performance during subsequent training or competition.
Strength and power athletes can also benefit from high glycemic carbohydrates. As previously mentioned insulin moves glucose from the blood to the tissue, inhibits the breakdown of fats to be used as a fuel source, and most importantly, blocks the degradation of proteins (muscle). This is beneficial to the resistance trained athlete by limiting muscle damage during exercise leading to improved recovery following training (1).
Even greater benefit is observed in both the endurance and the strength athlete when protein is added to the carbohydrate in a 3:1 - 4:1 carbohydrate/protein ratio (20 — 24 g carbohydrate to 5 — 6 g protein). It appears the consumption of protein with carbohydrate further reduces muscle damage during training leading to faster recovery following training, and further enhances glycogen replacement following exercise (1,4).
For maximum benefit, it is advised to begin consuming carbohydrate 10 minutes prior to the start of exercise and throughout the exercise session. Endurance athletes should consume a carbohydrate/protein supplement in a 4:1 ratio within the 45 minute window following exercise. Resistance trained athletes should consume 40 g of carbohydrates with 15 g of protein within the same 45 minute window (2). Of the protein supplements available, whey protein is recommended since it empties from the stomach faster than other protein supplements.
When consuming a carbohydrate supplement prior to and during exercise, it is important that the carbohydrate is both high glycemic and a liquid, such as a sports drink. However, sports drinks made with the sugar fructose should be avoided since fructose is slower to move from the stomach. Most sports drinks will provide the carbohydrates necessary for the desired insulin response, though only a few drinks are commercially available that provide both the carbohydrate and protein necessary for glycogen replacement and muscle recovery. Of course you can get carbohydrates and proteins from solid foods, but solids may not be practical and they take a lot of time to pass from the stomach, which could lead to gastrointestinal distress during exercise.
Continual carbohydrate and protein consumption is vital beyond the initial 45-minute post exercise period so the body has the proper nutrients to continue to repair and recover from training. High glycemic carbohydrates can still be consumed up to four hours following exercise, though it should be combined with a quality lean protein source. At this point a meal may be more beneficial at meeting the nutritional needs rather than supplement bars and drinks. For the remainder of the day any carbohydrates consumed should be low glycemic to maintain a constant and controlled rate of insulin release. An insulin spike is no longer desirable and should be avoided.
Keep in mind the glycemic index is not a rating of nutritional value. Some foods can be high glycemic and low in calories, (e.g. beets) while some foods are low glycemic but high in calories (e.g. peanut M&M's). Choose wisely.
References
1. Baty JJ, Hwang H, Ding Z, Bernard JR, Wang B, Kwon B, Ivy JL.(2007). The effect of a carbohydrate and protein supplement on resistance exercise performance, hormonal response, and muscle damage. Journal of Strength and Conditioning Research, 21(2):321 — 329.
2. Ivy J, Portman R. (2004). Nutrient Timing: The Future of Sports Nutrition. Basic Health. North Bergen, NJ.
3. McArdle WD, Katch FI, Katch VL. (1999). Sports & Exercise Nutrition. Lippincott, Williams & Wilkins. Baltimore, MD.
4. Saunders MJ, Luden ND, Herrick JE. (2007). Consumption of an oral carbohydrate-protein gel improves cycling endurance and prevents postexercise muscle damage. Journal of Strength and Conditioning Research, 21(3):678 — 684.
About the Author
Dr. Thomas W. Nesser is an assistant professor in the Department of Physical Education at Indiana State University where he develops and teaches advanced courses in strength and conditioning. He has been a member of the National Strength and Conditioning Association (NSCA) for the past 17 years and has been a certified strength and conditioning specialist (CSCS) for 14 years. Dr. Nesser is the NSCA state director for Indiana and serves on the NSCA Education Committee. Dr. Nesser is also a certified health fitness instructor through the American College of Sports Medicine (ACSM). He holds a master's degree in exercise science from the University of Nebraska at Omaha and a PhD in Kinesiology from the University of Minnesota. Dr. Nesser's research interests include the effects of training and the factors related to athletic performance
By Thomas W. Nesser, PhD, CSCS
The weight loss industry has classified carbohydrates as "good carbs" and "bad carbs". However, when it comes to athletic performance, there are no "bad carbs". All carbohydrates are equally important; the trick is understanding when one carbohydrate is better than another in relation to training.
Even though carbohydrates are the body's primary energy source, they are not the body's only source of energy. The body can also use fats and proteins for energy, though neither are as efficient as carbohydrates. Fats are a rich energy source, however it takes the body more time to breakdown fats to be used as an energy. In addition, the conversion of fat into energy requires a great amount of oxygen. Therefore fats are predominantly used during aerobic (endurance) exercise. While proteins can be used as an energy source, they are not the preferred source because it takes a lot of time for the body to break them down into a useable form. Besides, the protein used as an energy source comes from muscle breakdown. As an athlete, the breakdown of muscle mass is not desired.
When carbohydrates are consumed they are broken down to glucose and released into the blood stream. Carbohydrate sources include grains, fruits, vegetables, and sugar. Glycemic index (GI) is a measure of the rate at which specific carbohydrates are broken down to glucose and released into the blood stream. The ranking used is relative to pure glucose which has a ranking of 100. Carbohydrates with a high GI (e.g. corn flakes = GI value of 80) are rapidly broken down and released into the blood while those with a low GI (e.g. kidney beans = GI value of 29) are slower to break down and released into the blood. See table 1 for a list of carbohydrates and their glycemic score.
Table 1. Glycemic index of Common Foods
Food GI Rank
Peanuts 13
Kidney beans 29
Apple 39
Orange 40
Whole wheat pasta 42
Sweet potatoes 48
Peas 51
Corn 59
Banana 62
Raisins 64
Brown rice 66
White bread 69
White rice 72
Corn flakes 80
Honey 87
Carrots 92
Note: Differences exist in GI ranking due to the exact type of food tested3.
As blood sugar (glucose) levels increase, the pancreas releases insulin to move the glucose from the blood into the tissue where it is used as energy or stored as glycogen. It is important to note insulin also inhibits fat metabolism and protein breakdown. Foods with a high glycemic index are often accompanied by a spike of insulin. The excessive insulin pulls too much glucose from the blood causing fatigue, hunger, and usually additional sugar cravings. This cycle continues throughout the day impeding the use of fats as a fuel and ultimately leading to weight gain. This does not mean all high GI carbohydrates are bad and should be avoided.
High glycemic index foods are very beneficial when consumed prior to, during, and following exercise. During exercise, glycogen is broken down into glucose and released into the blood where it is carried to the working muscles to be used as energy. When an athlete eats a high GI food prior to or during exercise, the absorbed glucose is used as an immediate energy source to fuel the working muscles. Another benefit of consuming carbohydrates during exercise is to spare the use of stored carbohydrate (glycogen), allowing an individual to exercise longer without the risk of depleting glycogen stores.
Following exercise, high glycemic carbohydrates are recommended for quickly replenishing glycogen stores. Upon cessation of exercise there is a 45 minute window in which the body's capacity to replenish glycogen stores is greatest (2). After this optimal window, replenishing glycogen stores will take longer and may not be entirely complete by the next exercise bout which could hinder performance. Not having glycogen stores at full capacity could hinder performance during subsequent training or competition.
Strength and power athletes can also benefit from high glycemic carbohydrates. As previously mentioned insulin moves glucose from the blood to the tissue, inhibits the breakdown of fats to be used as a fuel source, and most importantly, blocks the degradation of proteins (muscle). This is beneficial to the resistance trained athlete by limiting muscle damage during exercise leading to improved recovery following training (1).
Even greater benefit is observed in both the endurance and the strength athlete when protein is added to the carbohydrate in a 3:1 - 4:1 carbohydrate/protein ratio (20 — 24 g carbohydrate to 5 — 6 g protein). It appears the consumption of protein with carbohydrate further reduces muscle damage during training leading to faster recovery following training, and further enhances glycogen replacement following exercise (1,4).
For maximum benefit, it is advised to begin consuming carbohydrate 10 minutes prior to the start of exercise and throughout the exercise session. Endurance athletes should consume a carbohydrate/protein supplement in a 4:1 ratio within the 45 minute window following exercise. Resistance trained athletes should consume 40 g of carbohydrates with 15 g of protein within the same 45 minute window (2). Of the protein supplements available, whey protein is recommended since it empties from the stomach faster than other protein supplements.
When consuming a carbohydrate supplement prior to and during exercise, it is important that the carbohydrate is both high glycemic and a liquid, such as a sports drink. However, sports drinks made with the sugar fructose should be avoided since fructose is slower to move from the stomach. Most sports drinks will provide the carbohydrates necessary for the desired insulin response, though only a few drinks are commercially available that provide both the carbohydrate and protein necessary for glycogen replacement and muscle recovery. Of course you can get carbohydrates and proteins from solid foods, but solids may not be practical and they take a lot of time to pass from the stomach, which could lead to gastrointestinal distress during exercise.
Continual carbohydrate and protein consumption is vital beyond the initial 45-minute post exercise period so the body has the proper nutrients to continue to repair and recover from training. High glycemic carbohydrates can still be consumed up to four hours following exercise, though it should be combined with a quality lean protein source. At this point a meal may be more beneficial at meeting the nutritional needs rather than supplement bars and drinks. For the remainder of the day any carbohydrates consumed should be low glycemic to maintain a constant and controlled rate of insulin release. An insulin spike is no longer desirable and should be avoided.
Keep in mind the glycemic index is not a rating of nutritional value. Some foods can be high glycemic and low in calories, (e.g. beets) while some foods are low glycemic but high in calories (e.g. peanut M&M's). Choose wisely.
References
1. Baty JJ, Hwang H, Ding Z, Bernard JR, Wang B, Kwon B, Ivy JL.(2007). The effect of a carbohydrate and protein supplement on resistance exercise performance, hormonal response, and muscle damage. Journal of Strength and Conditioning Research, 21(2):321 — 329.
2. Ivy J, Portman R. (2004). Nutrient Timing: The Future of Sports Nutrition. Basic Health. North Bergen, NJ.
3. McArdle WD, Katch FI, Katch VL. (1999). Sports & Exercise Nutrition. Lippincott, Williams & Wilkins. Baltimore, MD.
4. Saunders MJ, Luden ND, Herrick JE. (2007). Consumption of an oral carbohydrate-protein gel improves cycling endurance and prevents postexercise muscle damage. Journal of Strength and Conditioning Research, 21(3):678 — 684.
About the Author
Dr. Thomas W. Nesser is an assistant professor in the Department of Physical Education at Indiana State University where he develops and teaches advanced courses in strength and conditioning. He has been a member of the National Strength and Conditioning Association (NSCA) for the past 17 years and has been a certified strength and conditioning specialist (CSCS) for 14 years. Dr. Nesser is the NSCA state director for Indiana and serves on the NSCA Education Committee. Dr. Nesser is also a certified health fitness instructor through the American College of Sports Medicine (ACSM). He holds a master's degree in exercise science from the University of Nebraska at Omaha and a PhD in Kinesiology from the University of Minnesota. Dr. Nesser's research interests include the effects of training and the factors related to athletic performance
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