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Background and aims
 Physical exercise can cause large undulations in plasma glucose (PG) in persons with type 1 diabetes. High glycemic and/or high carbohydrate amounts are commonly advocated to rapidly raise PG ahead of exercise. Although low glycemic index carbohydrates have been explored, the impact of other macronutrient combinations on glycemic stability during exercise have been less studied. The aim of this study was to compare the effect of a pre-exercise low-carbohydrate-high protein (LCHP) meal versus a high-carbohydrate-low-protein (HCLP) meal on PG during and after exercise in persons with type 1 diabetes.

Materials and methods:
 Fourteen persons with insulin pump-treated type 1 diabetes (11 female, age 47 (range 25-65) years, HbA1c 51 (43-59) mmol/l, diabetes duration 30 (12-55) years, BMI 24.1 (19.3-27.1) kg/m2) completed a 2-arm randomised cross-over study. On each visit participants arrived in the morning and ingested either a LCHP (carbohydrate 21E%, protein 52E%, fat 27E%) or HCLP (carbohydrate 52E%, protein 21E%, fat 27E%) breakfast. Meals were isocaloric (bodyweight <75 kg: 425 Kcal; ≥75 kg: 520 Kcal). Basal insulin rate and meal bolus were reduced by 35% and 25%, respectively, according to international guidelines. After the meal, participants rested for 90 minutes and then cycled at 60% VO2peak for 45 min. Thereafter, participants rested for 180 minutes. During each study visit PG (figure 1), plasma insulin and plasma glucagon were measured at regular intervals.

Results:
 Average PG concentration was similar between LCHP and HCLP (9.64 ± 2.02 vs. 8.66 ± 2.03 mmol/l, P=0.142), but there was less PG variability after LCHP compared with HCLP (CV 14.81 ± 5.78 vs. 25.44 ± 8.23%, P=0.001). PG peak was similar between LCHP and HCLP (11.79 ± 2.21 vs 12.34 ± 2.57 mmol/l, P=0.488) but nadir was lower for HCLP (7.49 ± 1.88 vs. 5.51 ± 2.13 mmol/l, P=0.011). PG change from start to end exercise was less in LCHP compared with HCLP (1.56 ± 1.87 vs. 3.78 ± 2.03, P=0.002). In HCLP four episodes of PG<3.9 mmol/l were treated with 15 g carbohydrate and one episode of PG>15.0 mmol/l was treated with insulin bolus administration. In LCHP there was one hypoglycemia and one hyperglycemia rescue. PG values after rescue treatment were censored.

Conclusion:
 Compared with HCLP a LCHP pre-exercise meal lowers PG variability, diminishes the decrease in PG from start to end exercise, and reduces treatment-requiring hypoglycemia. This study shows the importance of taking into account the pre-exercise meal composition in the PG management during and after exercise in type 1 diabetes.