Consuming carbs within 30 minutes after exhaustive, glycogen-depleting exercise allows your muscles to more rapidly restore their glycogen and may actually prevent late-onset hypoglycemia that can occur up to 24 hours after exercise. Insulin sensitivity is generally heightened immediately after exercise, and during this time, your body’s blood glucose uptake into muscle to reform glycogen can be accomplished with minimal amounts of insulin circulating around. Good glycemic control during the post-exercise recovery period is essential to subsequent exercise performance, though, since you may experience reduced rates of net muscle glycogen repletion if your diabetes is poorly controlled during that time. To maintain glycemic control, you will probably need to take some additional insulin to cover the carbs that you eat post-exercise, albeit generally less than your usual doses.
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 you can't or won't lower your insulin levels
• 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 many carbs you took in during the activity
In summary, athletes who have diabetes and wish to optimize their athletic performance need to have 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 diabetic athlete. While a greater knowledge of these concepts provides a starting point for optimizing performance, effective exercise can only be achieved by athletes individually working to determine their own, unique glycemic responses. You’ll need to engage in frequent blood glucose monitoring (i.e., before, during, and after exercise), just like competitive diabetic athletes with well-established exercise routines do until you establish your own patterns and learn how to make adjustments to stay in control of your blood sugars.
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 version of this book will be available in November 2008 titled “The Diabetic Athlete’s Handbook.”