Baseline glucoregulatory function moderates the effect of dairy milk and fruit juice on postprandial cognition in healthy young adults

Purpose: Few studies have examined acute cognitive effects of dairy products. Prior work suggests baseline glucoregulatory function may moderate the relationship between macronutrient profile and postprandial cognition. This study examined the role of glucoregulatory function in postprandial cognition after milk, fruit juice, and a water control. We hypothesized juice would improve cognition in those with lower fasting glucose, while milk would improve cognition in those with higher fasting glucose. Design: 86 non-diabetic, non-hypoglycemic young adults attended three 8 AM testing sessions after fasting overnight. Fasting glucose was assessed via fingerstick at each session. Participants consumed 8 oz of 1% milk (12 g carbohydrates), apple juice (29 g carbohydrates), or water in a randomized, counterbalanced order, and completed repeatable standard and running memory continuous performance (SCPT—vigilance; RMCPT–working memory) and go/no-go (GNG–inhibitory control) tasks 30, 90, and 120 min post-ingestion. Results: Participants with fasting glucose above 107.69 mg/dL made significantly fewer GNG commission errors overall after milk versus water, while the converse was observed when fasting glucose was below 70.85 mg/dL (p = 0.003). At 30 min, participants with fasting glucose above 105.80 mg/dL made significantly more RMCPT correct responses per minute after milk versus juice, while the opposite occurred when fasting glucose was below 76.85 mg/dL (p = 0.006). For both tasks, differences greatened as fasting glucose increased or decreased beyond these upper and lower bounds, respectively. Conclusions: Consideration of baseline glucoregulatory function is crucial when assessing postprandial cognition, even in non-diabetic and non-hypoglycemic samples. Dairy milk may improve cognition in persons with higher fasting glucose.