Effect of Timing of Apple Juice Consumption on Postprandial Glycemia: A Randomized Crossover Trial

Background/Objectives: Fruit juice is commonly consumed with meals, yet its liquid matrix and rapidly absorbable carbohydrates may influence postprandial glycemic excursions. Whether altering the timing of fruit juice intake relative to a meal can attenuate postprandial glucose (PPG) remains unclear. This study aimed to investigate the effect of the timing of apple juice consumption on PPG in healthy adults. Methods: This randomized, two-period crossover trial (ChiCTR2600121025) enrolled 20 healthy adults in Beijing, China (March 2026), randomized 1:1; 19 with valid continuous glucose monitoring (CGM) data were analyzed. Each consumed 200 mL of 100% apple juice either 30 min before a standardized breakfast (preload) or with the same breakfast (co-ingestion), separated by a 4-day washout. Standardized lunch and dinner were provided. Blinding was not feasible. The primary outcome was breakfast peak glucose measured by CGM; secondary outcomes were incremental area under the curve (iAUC0–210), maximum excursion, and the corresponding lunch and dinner outcomes. Results: Preloading significantly reduced breakfast peak glucose versus co-ingestion (mean difference 0.51 mmol/L; 95% confidence interval [CI] 0.07–0.94; p = 0.025) and breakfast maximum glucose excursion (0.42 mmol/L; 95% CI 0.02–0.82; p = 0.040), but not iAUC0–210 (0.07 mmol/L·h; 95% CI −0.57 to 0.70; p = 0.830); no glycemic outcome differed at lunch or dinner. Conclusions: Consuming the same serving of apple juice 30 min before breakfast, rather than with it, reduced breakfast peak glucose and maximum glucose excursion. For individuals who already consume fruit juice, adjusting its timing relative to breakfast reduced breakfast peak glucose and maximum glucose excursion in this small sample; confirmation in larger trials is needed.