Characterizing the Use of Continuous Glucose Monitors During Experimentally-Induced Short-Term Low Energy Availability in Female Endurance Runners

Abstract

Female endurance runners are at high risk for low energy availability (LEA). Preliminary evidence suggests that fasting blood glucose (BG) concentration decreases in response to short-term energy deficiency (low energy availability). BG monitoring tools, such as continuous glucose monitors (CGM), could be used as an early detection device for LEA risk in athletes. PURPOSE: Characterize changes in BG over the course of five days in experimentally-induced LEA in female runners. METHODS: Recreational runners completed a 5-day experimental condition of LEA (15 kcal/kg FFM/d) achieved by a combination of dietary restriction and treadmill running at 65% VO2max. BG concentration was monitored every 15 min across the five experimental days using a CGM (Freestyle Libre Pro, Abbott), which assesses BG from interstitial glucose concentration. Glucose data from the 5-day condition were analyzed to obtain average 24- h BG, fasting BG, BG during sleep, "time in target" BG range (TIT), "time above target" range (TAT), "time below target" range (TBT), as well as glycemic variability using MAGE (mean of amplitude of glucose excursions) and MODD (mean of daily differences). 70 to 120 mg/dL was set as the target range. Data was analyzed using repeated measures analysis of variance; post hoc comparisons were performed using paired t-tests. RESULTS: Contrary to our hypothesis, our results suggest that five days of experimentally-induced LEA in female runners progressively increased 24- h BG and TIT while simultaneously altering patterns of fasting and sleeping BG. Average glucose concentration and TIT significantly increased from day one to day five (P=0.024 and P=0.03, respectively). Fasting and sleeping BG followed the same trends and significantly decreased from day one to day three (P=0.04 and P=0.002, respectively), followed by an increase by day five that was similar to day one. There was not a significant time-effect for MAGE, MODD, TBT, TBT, and glycemic variability (P>0.05). These changes are likely due to alterations in glucose production versus utilization that are driven by decreased insulin and/or increased BG counterregulatory hormones. This study is the first to characterize glycemia during short-term experimentally-induced LEA in female endurance runners using a CGM; emphasizing the potential ability of CGMs to gain insight on BG patterns during conditions of LEA.