Addressing how to balance blood glucose levels during (and after) exercise with type 1 diabetes is not new. In fact, it is likely the KEY topic to address to be successful at being physically active if you take exogenous insulin and want to prevent hypoglycemia or hyperglycemia during exercise. Strategies include changing insulin doses and/or supplementing with food, either of which can be done in myriad ways depending on the activity, timing and more.
A recent 2020 study revisited whether it works better to supplement with carbohydrates or lower bolus (mealtime) insulin doses before exercise to prevent lows (1). Its conclusion—for this particular group of subjects doing continuous, moderate-intensity cycle ergometer exercise for ∼45 minutes—was that taking in 15 to 30 grams of carbohydrate when blood glucose levels decreased to 7.0 mmol/L (126 mg/dL) prevented hypoglycemia better. Okay, but….
My issue with these types of studies is not that they don‘t prove a point—they do—but it‘s that they prove a very, very narrow point. The results can only be generalized to people with the same physical fitness level, age, sex, and diet undertaking a specific type, intensity, duration, and timing of activity. Exercising with type 1 diabetes is so much broader than that. Moreover, it‘s not just short-term insulin dosing or immediate carbohydrate intake that has an impact on balancing blood glucose and affecting how successful you are at being active.
Whether participating in sports or physical activity on a recreational basis or striving to be a professional or Olympic athlete, anyone who takes insulin must pay attention to his or her unique nutritional and dietary patterns, including intake of macronutrients (carbohydrate, protein, and fat), micronutrients (vitamins and minerals), fluids, and supplements like caffeine to maintain metabolic and glycemic balance (2). Athletic performance aside, nutritional recommendations may also differ on an individual basis relative to exercise, glycemic management, and body weight goals. Balancing all these dietary factors can be challenging for individuals with type 1 diabetes, and many related aspects have yet to be thoroughly researched in this population.
Carbohydrates undeniably have the most immediate impact on blood glucose. They must be matched with adequate insulin doses to manage blood glucose peaks after eating (3), but protein and fat intake can impact insulin needs as well (4). When you‘re an active individual with type 1 diabetes, you must balance all your dietary choices before, during, and after exercise to manage blood glucose levels not just to prevent lows or highs, but also for optimal performance and recovery from working out or competing. It‘s possible to eat many different ways, including low-carbohydrate (5), and the best nutritional practices to optimize performance may or may not be best for blood glucose management, optimal health, and bodyweight simultaneously, potentially making achieving athletic and health goals difficult at times.
As for insulin dosing, people vary so much about their usual doses, insulin sensitivity, types of insulin used (basal and bolus choices), delivery (that is, insulin pump use vs. injections or inhalation), and more. It makes the whole balancing act that much more difficult, especially when blood glucose responses vary with the type of activity being done, including how long, how hard, how often, and under which environmental conditions. Even hydration status matters! Given how limited studies by nature must be to limit all these conditions, it takes individual trial-and-error to figure out what works best to maintain blood glucose levels in a reasonably tight (and hopefully normal) range for every single activity bout.
Many insulin users have still managed to figure out how to compete athletically at the highest levels. However, it is far from simple when balancing blood glucose levels with these many confounding variables (6). It‘s certainly still worth it to be physically active with type 1 diabetes, just a challenge!
- Eckstein ML, McCarthy O, Tripolt NJ, et al. Efficacy of carbohydrate supplementation compared with bolus insulin dose reduction around exercise in adults with type 1 diabetes: A retrospective, controlled analysis. Can J Diabetes, 2020 (in press), https://doi.org/10.1016/j.jcjd.2020.03.003.
- Colberg SR, Nutrition and exercise performance in individuals with type 1 diabetes. Can J Diabetes, 2020 (in press), https://doi.org/10.1016/j.jcjd.2020.05.014.
- Bell KJ, King BR, Shafat A, Smart CE. The relationship between carbohydrate and the mealtime insulin dose in type 1 diabetes. J Diabetes Complications. 2015;29(8):1323-9, https://doi.org/10.1016/j.jdiacomp.2015.08.014.
- Bell KJ, Smart CE, Steil GM, Brand-Miller JC, King B, Wolpert HA. Impact of fat, protein, and glycemic index on postprandial glucose control in type 1 diabetes: implications for intensive diabetes management in the continuous glucose monitoring era. Diabetes Care. 2015;38(6):1008-15, https://doi.org/10.2337/dc15-0100.
- Scott SN, Anderson L, Morton JP, Wagenmakers AJM, Riddell MC. Carbohydrate restriction in type 1 diabetes: A realistic therapy for improved glycaemic control and athletic performance? Nutrients. 2019;11(5):1022, https://doi.org/10.3390/nu11051022.
- Riddell MC, Scott SN, Fournier PA, et al. The competitive athlete with type 1 diabetes [published online ahead of print, 2020 Jun 12]. Diabetologia. 2020;10.1007/s00125-020-05183-8, https://doi.org/10.1007/s00125-020-05183-8.
Sheri R. Colberg, Ph.D., is the author of The Athlete’s Guide to Diabetes: Expert Advice for 165 Sports and Activities (the newest edition of the Diabetic Athlete‘s Handbook). She is also the author of Diabetes & Keeping Fit for Dummies, co-published by Wiley and the ADA. A professor emerita of exercise science from Old Dominion University and an internationally recognized diabetes motion expert, she is the author of 12 books, 30 book chapters, and over 420 articles. She was honored with the 2016 American Diabetes Association Outstanding Educator in Diabetes Award. Contact her via her websites (SheriColberg.com and DiabetesMotion.com).