Variability in interstitial fluid glucose response to an acute change in energy availability in endurance athletes

Objectives To determine whether an acute change in energy availability (EA) causes perturbations in interstitial glucose in athletes. Methods Using a randomized crossover design, five trained endurance athletes (n = 3 men, 26.4 ± 7.5 y, VO2 max 53.1 ± 4.7 mL·kg-1·min-1), completed a morning high-intensity interval cycling session (AM HIT; 6 × 5 min @ 85% VO2 max) and an afternoon steady-state cycling session (PM SS; 80 min @ 63% VO2 max) under dietary conditions of either (1) high energy availability (HEA: 42.6 ± 3.8 kcal·kg-1 FFM·d-1, 10.0 ± 1.4 g·kg-1·CHO) or (2) low energy availability (LEA: 11.3 ± 2.4 kcal·kg-1 FFM, 5.2 ± 0.3 g·kg-1·CHO) following 3 days of dietary harmonization (DH; 46.1 ± 1.5 kcal·kg-1 FFM·d-1, 8.3 ± 0.6 g·kg-1·CHO). Interstitial glucose data was measured with Freestyle Libre 2 continuous glucose monitors (Abbott Diabetes Care, Chicago IL; CGM’s) with 15-min epochs to determine glycemic variability, calculated as mean interstitial glucose (MG), mean amplitude of glycemic excursions (MAGE), and coefficient of variation (CV). Results CGM-derived overnight MG was lower during LEA and HEA compared to DH (LEA 4.5 ± 0.3 mmol·L-1 HEA 4.9 ± 0.1 mmol·L-1 vs 5.5 ± 0.4 mmol·L-1; P = 0.01, d > 1.9). MAGE was lower in the LEA trial compared to HEA, although this was not statistically significant (1.7 ± 0.7 mmol·L-1 vs 2.1 ± 0.3 mmol·L-1, P = 0.26, d = 0.8). Conclusions. Contrary to our hypothesis, perturbations to overnight glucose variability occurred in both LEA and HEA conditions which may be related to changes in daily training load compared with athletes’ habitual training.