Postprandial Variability of Cognitive Inhibitory Control following Dairy Milk versus Fruit Juice in Children

Background Prior research suggests a complex relationship between macronutrient profile and postprandial cognition, involving influences of glucoregulation, body mass index (BMI), and potential sex differences. Recent work demonstrates potential benefits for cognition after consuming dairy compared to a fruit juice beverage (i.e., apple juice). The current study examined the effects of 1% milk versus apple juice on variability in inhibitory control performance over time among healthy school‐age children. We predicted that milk would promote more stable performance over time compared to juice. We further examined how body mass index (BMI), glucoregulation, and sex influence performance in each beverage condition. Methods Eighty‐five English‐speaking children ages 8–12 attended two 8 AM testing sessions after fasting overnight. During each session, participants consumed 8oz of either 1% milk or apple juice in a randomized, counterbalanced fashion. Blood glucose was measured via fingerstick, and cognitive performance was assessed using a Go/No‐Go (GNG) paradigm prior to beverage consumption. GNG performance was then re‐assessed 30, 90, and 120 minutes post‐consumption. Variability in cognitive performance was operationalized as the standard deviation of reaction time (SDRT) during each GNG administration. Height and weight were assessed before beverage consumption at the baseline visit, and BMI was calculated. Results An unconditional linear growth curve model examined changes in SDRT in each beverage condition; this model demonstrated good fit (χ 2 (22) = 27.07, p = .21; RMSEA = .05; CFI = 0.99). Analyses revealed a linear increase over time in SDRT following juice (estimate = 3.76, SE = 0.51, p < .001) and milk (estimate = 3.51, SE = 0.56, p < .001). Significant between‐subject differences in baseline SDRT and change in SDRT over time were observed in both beverage conditions (all p s < .015); a second model therefore examined whether these between‐person differences could be explained by BMI, sex, or baseline glucose levels. This second model also demonstrated good fit (χ 2 (42) = 48.81, p = .21; RMSEA = .04; CFI = 0.99). While a linear increase in variability over time was still observed in the juice condition (estimate = 9.74, SE = 4.30, p = .02), such a trend was no longer observed in the milk condition ( p = .17). Greater BMI was associated with lower baseline SDRT in the milk condition ( b = −1.61, SE = 0.78, p = .04), and females showed greater baseline SDRT in the juice condition ( b = 22.01, SE = 6.09, p < .001). Baseline glucose was unassociated with baseline or change in SDRT in either condition. Notably, significant between‐subject differences in baseline and change in SDRT remained in both conditions, despite the addition of these covariates. Conclusions Our results suggest that, after adjusting for sex, BMI, and glucoregulation, inhibitory control performance is more stable over time following milk versus apple juice in school‐age children. Milk may facilitate consistent performance in children with higher BMI, while juice may negatively impact consistency of performance in females compared to males. Future studies utilizing larger samples may help identify additional determinants of between‐person differences in postprandial cognition and clarify the mechanisms of these findings. Support or Funding Information This work was supported by the National Dairy Council under Grant #2356.