In the past, most elite athletes attempted to improve performance through strategies to achieve “high CHO availability,“ meaning building up adequate pre-exercise glycogen levels and carbohydrate intake during the competition to meet fuel needs (think pasta parties the night before and high carb intake during events and competitions). More recently, many have aimed instead for a strategy called “low CHO availability“ to potentially enhance the adaptive responses to training or recovery with low carbohydrate intake and storage in muscles, often achieved with the periodization of carbohydrate intake (1). Periodically doing endurance training with reduced carbohydrate availability but competing without carbohydrate intake restrictions (i.e., training low-carb and competing high-carb) may promote superior metabolic training adaptations compared with a high carbohydrate intake all the time, at least in athletes without diabetes (2). How well these strategies work for athletes with diabetes is unknown. However, limiting carbohydrate intake after training can increase the incidence of nighttime blood glucose lows in insulin users (3).
Supplementing carbohydrates on an “as–needed basis“ during endurance activities may assist active individuals following a low-carb diet while training (2). Individuals with type 1 diabetes have been shown to effectively balance their blood glucose levels while supplementing 75 grams of carbohydrate per hour of multi-day and prolonged activities, even though higher insulin levels may be required to maintain normal blood glucose levels (4, 5). For intermittent sports like soccer, consuming 30 to 60 grams of carbohydrate per hour may prevent the fatigue or hypoglycemia that can occur toward the end of a game, at least in athletes without diabetes. Adapting to chronically low intake of carbohydrate results in higher rates of fat oxidation and use in elite ultra–endurance athletes, even though their use of muscle glycogen during training is not lower and muscle glycogen repletion during and after a 3-hour run is similar to athletes with a higher carbohydrate diet (6). However, an enhanced ability to use fat as fuel after adapting to a low-carb diet may or may not improve performance, even if performance during competitions and events is maintained. Research lacks such long-term adaptations and performance in athletes with diabetes, but the assumption is that if blood glucose levels are well managed, responses should be similar.
Adapted from Colberg SR, Nutrition and exercise performance in adults with type 1 diabetes. Canadian Journal of Diabetes, 44(8):750-758, 2020 (https://doi.org/10.1016/j.jcjd.2020.05.014)
- JeukendrupAE. Periodized Nutrition for Athletes. Sports Medicine. 2017;47(Suppl 1):51-63.doi: 10.1007/s40279-017-0694-2. PubMed PMID: 28332115.
- ImpeySG,Hearris MA, Hammond KM, Bartlett JD, Louis J, Close GL, et al. Fuel for the Work Required: A Theoretical Framework for Carbohydrate Periodization and the Glycogen Threshold Hypothesis. Sports Medicine. 2018;48(5):1031-48. doi: 10.1007/s40279-018-0867-7. PubMed PMID: 29453741.
- Scott SN, Anderson L, Morton JP,WagenmakersAJM, Riddell MC. Carbohydrate Restriction in Type 1 Diabetes: A Realistic Therapy for Improved Glycaemic Control and Athletic Performance? Nutrients. 2019;11(5):1022. doi: 10.3390/nu11051022. PubMed PMID: 31067747.
- AdolfssonP,Mattsson S, Jendle J. Evaluation of glucose control when a new strategy of increased carbohydrate supply is implemented during prolonged physical exercise in type 1 diabetes. Eur J Appl Physiol. 2015;115(12):2599-607. doi: 10.1007/s00421-015-3251-4. PubMed PMID: 26341091.
- MattssonS,Jendle J, Adolfsson P. Carbohydrate Loading Followed by High Carbohydrate Intake During Prolonged Physical Exercise and Its Impact on Glucose Control in Individuals With Diabetes Type 1-An Exploratory Study. Front Endocrinol. 2019;10:571. doi: 10.3389/fendo.2019.00571. PubMed PMID: 31496994; PubMed Central PMCID: PMCPMC6712943.
- Chang CK, Borer K, Lin PJ. Low-Carbohydrate-High-Fat Diet: Can it Help Exercise Performance? J HumKinet.2017;56:81-92.(doi):10.1515/hukin-2017-0025.
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 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).