Carbohydrate supplementation is superior to bolus insulin reductions for the prevention of hypoglycemia during exercise in people with type 1 diabetes (T1D), according to retrospective study results published in the Canadian Journal of Diabetes.

Studies have introduced reductions in bolus or basal insulin doses prior to exercise and threshold-based carbohydrate supplementation during exercise as a method for adults and adolescents with T1D to reduce the risk for exercise-induced hypoglycemia. The efficacy of one method over the other has not yet been determined.

Data from 2 clinical trials were analyzed to compare these methods. A total of 18 adults with T1D on stable basal insulin degludec and bolus insulin aspart therapy were assigned to 1 of 3 exercise groups matched for age, diabetes duration, hemoglobin A1c (HbA1c) level, and body mass index (BMI).

Group A supplemented 15 to 30 g of fluid carbohydrate or glucose gel at a glycemic threshold of 7.0 mmol/L during the exercise session with no pre-exercise bolus insulin reduction. The group consisted of 9 patients (55.6% men) with an average age of 32.1±9 years, diabetes duration of 19±11 years, HbA1c of 7.2±2.8%, and BMI of 25.5±3.8 kg/m2.

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Groups B and C included the same 9 patients tested in a crossover design in which bolus insulin doses were either reduced or unadjusted before exercise with a minimum washout period of 1 week between each exercise session. The patients in this group (66.7% men) had an average age of 32.8±10 years, diabetes duration of 14±9 years, HbA1c levels of 7.3±1.4%, and BMI of 25.9±3.1 kg/m2.

The patients in group A consumed their last carbohydrate-rich meal with their regular carbohydrate to bolus insulin dose (1 g carbohydrate per kg bodyweight) at least 2 hours prior to the exercise session. Group A’s exercise procedure consisted of a 3-minute passive warm-up, a 3-minute active warm-up, 49 minutes at the individual target workload, a 3-minute active cool-down, and a 3-minute passive cool-down.

Patients in group B reduced their regular bolus insulin dose by 50% at 1 hour prior to the exercise session with their last meal (1 g carbohydrate per kg bodyweight). Group C served as a control with no adjustment to bolus insulin dose or carbohydrate consumption. Patients in group C also consumed their last meal 1 hour prior to the exercise session (1 g carbohydrate per kg bodyweight). Group B and C’s exercise procedure was similar to that of Group A, but with only 42 minutes at the target workload and with no 3-minute active cool-down.

During the exercise sessions, blood glucose level was measured every 6 to 7 minutes and interstitial glucose was intermittently scanned by the monitoring device worn by all participants.

Blood glucose levels prior to the start of exercise were similar between groups. The quantity and duration of hypoglycemic events was recorded for each participant. The number of hypoglycemic events was significantly higher in Group B (P = .02) and Group C (P =.02) compared with Group A. The median blood glucose concentration during exercise was lower in Group C (P =.01), but not significantly lower in Group B compared with Group A. The average time spent in euglycemia was 100% in Group A compared with 71% in Group B and 62% in Group C.

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Overall, the study results indicated that carbohydrate supplementation was more effective than bolus insulin dose reductions to prevent hypoglycemia during moderate-intensity exercise in individuals with T1D. This method has the additional benefit of being easier to implement as it does not require additional planning or changes to an individual’s insulin therapy.

A limitation to this study was the slight difference in experimental design for Group A and Groups B and C because of the use of data from 2 independent study designs. Studies with larger sample sizes, consistent study design, longer study duration, and various types of exercise are warranted.

Disclosure: Novo Nordisk funded the studies that provided data for this analysis. Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.

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Eckstein ML, McCarthy O, Tripolt NJ, et al. Efficacy of carbohydrate supplementation compared to bolus insulin dose reduction around exercise in adults with type 1 diabetes: a retrospective controlled analysis [published online February 22, 2020]. Can J Diabetes. doi:10.1016/j.jcjd.2020.03.003