Short-term effects of carbohydrates differing in glycemic index (GI) consumed at lunch on children's cognitive function in a randomized crossover study

Background: Intervention studies suggest that breakfast dietary glycemic index (GI) can influence children's cognition. The Cognition Intervention Study Dortmund-GI-I examined whether lunch dietary GI exerts short-term effects on selected cognitive parameters. Methods: In a randomized, single-blind, 2×2 crossover study conducted on two test days at a comprehensive school, 189 5th–6th graders were randomized to sequences medium–high GI (m–hGI) or high–medium GI (h–mGI) using block randomization. In period 1 one group received high-GI rice (GI 86) and the other medium-GI rice (GI 62) ad libitum; vice versa in period 2 one week later. Tonic alertness, task switching, and working memory updating were tested with a computerized battery 45 minutes after the start of lunch break. Treatment effects were analyzed using t tests or Wilcoxon rank-sum tests. Results: In the crossover analysis, no effects of lunch dietary GI on the cognitive parameters were observed in the early afternoon. Carryover effects were detected for two parameters; therefore, first-period data were analyzed separately. In period 1, the high-GI group showed faster reaction time in the two-back task (p = 0.001) and fewer commission errors in the alertness task (p = 0.04). Conclusion: No evidence of short-term effects of lunch dietary GI on overall cognition in schoolchildren was found; potential positive effects on specific parameters (working memory updating and tonic alertness) favoring high-GI rice require verification.