Objective: Studies indicate that eating lunch impairs some aspects of adults' cognitive functioning. However, the short-term effects of lunch on children's executive functions (EF) have not been examined. The Cognition Intervention Study Dortmund PLUS (CogniDo PLUS) investigated (a) short-term effects of lunch on EF in children and (b) whether the postprandial cortisol increase mediates putative lunch effects on EF performance.
Methods: 5th and 6th grade students of a comprehensive school in Gelsenkirchen (Germany) participated in the randomized crossover intervention study. On Day 1 of the study, Group 1 did not eat lunch,whereas Group 2 received lunch ad libitum. One week later on Day 2 the groups were treated vice versa. At the beginning of the afternoon lessons, the EF parameters task switching,working memory updating and inhibition were tested using a computerized test battery. Saliva samples were used to measure cortisol directly before lunch and again at the beginning of the cognitive assessment. Of the 215 initially recruited children 21 dropped out of the study due to illness or absence on one of the two test days.
Results: Lower ratios of false alarms in the working memory updating function were observed when children who ate lunch than for children who had no lunch (8.2% (lunch) versus 9.4% (no lunch), p b 0.01). Parameters of task switching and inhibition did not differ between children who ate lunch compared to children who had no lunch. Stratification according to postprandial cortisol increase showed that the subgroup with a high increase had lower ratios of false alarms after eating lunch, while false alarm values did not change in the group with a low increase.
Conclusion: In contrast to findings in adults, the results indicate that children's EF are not impaired by lunch under true-to-life conditions. On the contrary, the current study even indicates beneficial effects of lunch intake for the working memory updating. The postprandial cortisol increase in the range observed in our sample does not seem to be related with negative effects on the performance of EF, but even seem to mediate the beneficial effect of lunch on the working memory updating.
Keywords: Children; Cognition; Cortisol; Executive functions; Lunch.