Author(s): HAMILTON, R., BRACKEN, R., Institution: SWANSEA UNIVERSITY, Country: IRELAND, Abstract-ID: 2469

INTRODUCTION:
Continuous Glucose Monitoring (CGM) has gained rapid interest in sports nutrition. CGM measures interstitial glucose as a proxy for blood glucose concentrations. However, consumption of large volumes, high concentration, or high glycaemic index carbohydrate containing solutions may alter the accuracy of the blood to interstitial glucose relationship observed when fasted or post-prandial due to the rapidly changing glucose environments. Thus, this study compared interstitial glucose and blood glucose responses to consumption of carbohydrate-containing beverages in humans.
METHODS:
Ten healthy adults (9 males, age 22 ± 1, height 177±12 cm, body mass 75±14 kg) attended the laboratory on seven occasions to consume 0g, 10g & 25g dextrose in 500 ml water, 10% & 20% carbohydrate solutions, and 10% low- (isomaltulose) or 10% high- (dextrose) glycaemic index carbohydrates in a double-blind, randomised, counterbalanced fashion. Capillary blood was collected at rest and over a subsequent 2-h period and analysed for glucose concentration (EKF Diagnostics). Concurrently, interstitial glucose concentrations were recorded (SupersapiensTM, TT1 Products Inc., Atlanta, GA, USA). Glycaemic parameters were compared between both fluid compartments. Mean absolute relative difference (MARD) was determined for periods of hypoglycaemia (<4mM), euglycaemia (4-7.88 mM) and hyperglycaemia (>7.88mM). Plasma volume changes were estimated (Dill & Costill 1974). Data were analysed using ANOVA with Bonferroni correction, and P≤0.05 accepted as significant.
RESULTS:
There was a slower time to reach peak glucose concentration in interstitial fluid than blood in 3 of the above carbohydrate consumption trials. Point concentration differences were lower in interstitial fluid than blood in the 25g (iG: 3.47±0.32 vs. BG: 3.75±0.20 mM , P=0.035) and 20% carbohydrate trials (iG: 3.35±0.29 vs. BG: 3.81±0.46 mM, P=0.015). MARD values were 14±16% across all timepoints, 20±28% in hypoglycaemia, 12.2±11.4% in euglycaemia and 14±16% during hyperglycaemia. MARD was greater during hypoglycaemia than during Euglycaemia (p>0.001) and all collective timepoints (p>0.001). Plasma volume changes were similar between carbohydrate trials.
CONCLUSION:
These data reveal differences in the interstitial glucose to blood glucose concentrations following carbohydrate beverage consumption. Further, there is a time lag between interstitial and blood glucose concentrations. Finally, mean absolute relative differences were highest in hypoglycaemia. These data suggest caution in the use of continuous glucose monitoring during fast changing glucose environments such as carbohydrate beverage consumption.

Dill DB, & Costill DL. (1974). Calculation of percentage changes in volumes of blood, plasma, and red cells in dehydration. Journal of Applied Physiology, 37(2), 247-248.