A Comparison of the Interstitial and Blood Glucose Responses Following Consumption of Different Carbohydrate-Containing Beverages in Humans: A Randomised Controlled Trial

Objectives: This study investigated the relationship between interstitial and blood glucose concentrations following ingestion of carbohydrate-containing drinks differing in carbohydrate amount, osmolarity, and glycaemic index. Methods: Ten healthy adults (nine male; age: 22 ± 1 y; height: 177 ± 12 cm; weight: 75 ± 14 kg) completed a double-blind, randomised cross-over study with seven beverage trials varying in carbohydrate (CHO) characteristics. Blood samples were collected at rest and over two hours, while interstitial glucose ([iG]) was recorded using a continuous glucose monitor (Supersapiens, Atlanta, USA). Glycaemic metrics and mean absolute relative difference (MARD) were calculated for hypoglycaemic, euglycaemic, and hyperglycaemic ranges. Data were analysed using repeated-measures ANOVA with Bonferroni correction and paired t-tests (p ≤ 0.05). Results: Interstitial and blood glucose concentrations were similar at baseline but diverged post-ingestion. MARD varied by glucose rate and direction, exceeding 20% during rapid declines (>2 mg/dL/min), where [iG] underestimated [BG] by −7.3 ± 27.1 mg/dL. Accuracy was highest during stable glucose (MARD = 10.5 ± 8.6%). Carbohydrate amount and glycaemic index influenced peak glucose, whereas beverage concentration (5–20%) had minimal effect when CHO amount was fixed, though variation in CGM agreement appeared during post-peak declines. Conclusions: CGM tracked blood glucose overall but showed reduced accuracy during rapid falls or hypoglycaemia. Carbohydrate properties influenced glycaemic response but not sensor agreement when CHO load was constant. Glucose rate and direction of change are key considerations for interpreting CGM data in research and applied settings.