This week Dr. Sheri Colberg, Ph.D., FACSM brings us part 3 of a series on Working with Diabetic Athletes- Nutritional Concerns in Athletes with Diabetes
Working with Diabetic Athletes: Part 3
Nutritional Concerns in Athletes with Diabetes
By Sheri Colberg, Ph.D., FACSM
As previously discussed in the past two columns, exercise can cause hypoglycemia, requiring additional carbohydrate intake for its treatment. Ingestion of supplemental carbohydrates before, during, and/or after exercise, however, may eventually contribute to excess caloric intake and weight gain. To replace carbohydrates optimally without excessive weight gain and to achieve optimal performance, hypoglycemia is best avoided by combining a lesser carbohydrate intake with a concomitant reduction in insulin. Adequate hydration is also important to performance. As a rule of thumb, to prevent dehydration, no more than six to eight ounces of cool, dilute fluids (e.g., water or sports drinks) should be consumed every 10 to 15 minutes during prolonged activities, particularly in warm or hot environmental conditions.
Athletes are known for taking various ergogenic supplements to potentially enhance their performance. Some of these nutritional supplements, however, can cause potential harm to an athlete with diabetes. For example, protein and amino acid supplements add extra stress on the kidneys due to the required excretion of excess amounts of nitrogen released when these supplements are metabolized. Such excretions can cause additional strain on kidneys with any pre-existing damage from long-term diabetes. Similarly, creatine monohydrate supplementation can harm already damaged kidneys, particularly during the initial creatine loading period, although the actual effect has not been tested in humans. Athletes with and without diabetes also frequently use caffeine to enhance their performance. Care must be taken with its use, though, as its use prior to exercise may cause excessive water loss and dehydration in a hot environment if adequate fluids are not consumed. When taken during exercise, though, its diuretic effect is not evident, nor is its impact on insulin action, making it an effective ergogenic for most exercisers.
Athletes with diabetes, like their non-diabetic counterparts, frequently utilize the practice of carbohydrate loading prior to competition. However, with insulin users it can cause hyperglycemia before, during, and/or after exercise if adequate insulin is not taken. Recent studies have shown that athletes loading with a diet comprised of 50 percent of the calories from carbohydrate intake actually maintain better glycemic control and have greater glycogen stores than those who take in a 60 percent carbohydrate diet. Liver glycogen repletion is also linked to tighter blood glucose control. Moreover, carbohydrate loading before and after exercise reduces the body’s formation of glucose transport proteins (GLUT4) and insulin sensitivity.
Conversely, hypoglycemia can occur if carbohydrate is consumed before exercise and excessive compensatory insulin is given. As prevention for, and treatment of hypoglycemia, athletes should always carry a supply of rapidly absorbable carbohydrate (e.g., glucose tablets, glucose polymers, sports drinks, juice, regular soda, and hard candy) that can be easily consumed before, during, and after physical activities.
Consuming carbohydrate within thirty minutes after exhaustive, glycogen-depleting exercise allows for more rapid restoration of muscle glycogen and may actually prevent late-onset hypoglycemia that can occur up to 24 hours after exercise. Insulin sensitivity is generally heightened immediately post-exercise, and during this time, blood glucose uptake into muscle to reform glycogen can be accomplished with minimal circulating insulin. Good glycemic control during the post-exercise recovery period is essential to subsequent exercise performance, since reduced rates of net muscle glycogen repletion are experienced in individuals with poorly controlled type 1 diabetes. To maintain glycemic control, some additional insulin may be needed to cover carbohydrate intake post-exercise, albeit generally less than usual is needed.
Guidelines for Fluid and Carbohydrate Ingestion for Physical Activity
• Consume adequate fluids before, during and following exercise to help prevent dehydration during exercise, particularly when hyperglycemic
• During hot weather, consume sports drinks containing electrolytes during exercise lasting longer than 60-90 minutes; otherwise consume cool water unless additional carbohydrate is needed to treat or prevent hypoglycemia
Carbohydrate before Exercise
• Carbohydrate intake a few hours before exercise generally benefits endurance capacity when taken along with adequate insulin
• Ingestion of extra carbohydrate prior to exercise is recommended if blood glucose levels are <100 mg/dl (5.5mM), but only if insulin cannot be lowered
• Avoid food with a high fiber or fat content before (and during) exercise
Carbohydrate during Exercise
• During exercise lasting more than 45 minutes, use a carbohydrate drink or snack to avoid low blood glucose and to improve exercise tolerance
• Consume about 10-15 grams of carbohydrate every 15-30 minutes during activity, modified for each athlete based on insulin regimen and exercise type
Carbohydrate after Exercise
• Following exercise, modest amounts of carbohydrate (along with insulin, as needed) should be ingested to minimize the risk of later-onset hypoglycemia
• Post-exercise carbohydrate needs will vary depending upon blood glucose levels and how much carbohydrate was consumed during the activity
In summary, working with athletes who have diabetes to optimize their athletic performance requires a greater understanding of exercise factors, such as the effects of circulating insulin levels on exercise responses, physiological response to different types of activities and training, and nutritional concerns specific to the athlete with diabetes. While a greater knowledge of these concepts provides a starting point for optimizing performance, effective exercise can only be achieved by working with athletes individually to determine their unique glycemic responses. Frequent blood glucose monitoring (i.e., before, during, and after exercise) is necessary and common even among competitive diabetic athletes with well-established exercise routines.
For more information about participation of diabetic exercisers in a variety of sports and recreational physical activity (along with real-life athlete examples), please consult The Diabetic Athlete: Prescriptions for Exercise and Sports (Human Kinetics, 2001) by Sheri Colberg. A fully revised and expanded 2nd Edition of this book will be available in Fall 2008.