Background and Aim

Exercise improves glycemic control and cardiovascular risk profiles in individuals with type 1 diabetes (T1D), yet plasma glucose fluctuations and fear of hypoglycemia remain major barriers to physical activity. Carbohydrate ingestion prior to exercise is recommended to reduce hypoglycemia risk, but conventional carbohydrate strategies often induce pre-exercise hyperglycemia followed by rapid glucose declines during exercise. Low-glycemic index carbohydrates may represent a more physiologically stable alternative. Lactose and galactose are milk-derived low-glycemic index carbohydrates with distinct metabolic characteristics that may provide such a stable alternative. The aim of this work was to examine lactose and galactose as pre-exercise carbohydrate strategies in individuals with T1D and to use T1D as a clinical model to explore their metabolic potential during exercise.

Methods

Adults with T1D completed standardized endurance exercise sessions following ingestion of dextrose, lactose, galactose, or placebo in a randomized, double-blind, crossover design. Glycemic responses were assessed using frequent blood sampling, while substrate utilization was evaluated by indirect calorimetry. Results

Compared with dextrose, lactose and galactose provided more stable glycemic responses during exercise, characterized by reduced hyperglycemic excursions and increased time in range. Both milk sugars also reduced time below range compared with placebo.

Conclusions

Milk sugars act as metabolically distinct pre-exercise carbohydrates in T1D, offering more stable glucose support during exercise. These findings highlight lactose and galactose as promising exercise fuels and position T1D as a valuable human model for revealing physiologically meaningful differences between carbohydrate types during exercise.