The effect of carbohydrate, protein and fat ingestion on simple as well as complex cognitive functions and the relationship between the respective postprandial metabolic changes and changes in cognitive performance were studied in fifteen healthy male students. Subjects were tested in three sessions, separated by 1 week, for short-term changes in blood variables, indirect calorimetry, subjective performance and different objective performance tasks using a repeatedmeasures counterbalanced cross-over design. Measurements were made after an overnight fast before and hourly during 3 h after test meal ingestion. Test meals consisted of either pure carbohydrates, protein or fat and were served as isoenergetic (1670 kJ) spoonable creams with similar sensory properties. Most aspects of subjective performance did not differ between test meals. For all objective tasks, however, postprandial cognitive performance was best after fat ingestion concomitant with an almost constant glucose metabolism and constant metabolic activation state measured by glucagon:insulin (G:I). In contrast, carbohydrate as well as protein ingestion resulted in lower overall cognitive performance, both together with partly marked changes P , 0´001 in glucose metabolism and metabolic activation. They also differently affected specific cognitive functions P , 0´05 in relation to their specific effect on metabolism. Carbohydrate ingestion resulted in relatively better short-term memory and accuracy of tasks concomitant with low metabolic activation, whereas protein ingestion resulted in better attention and efficiency of tasks concomitant with higher metabolic activation. Our findings support the concept that good and stable cognitive performance is related to a balanced glucose metabolism and metabolic activation state.
Cognitive performance: Macronutrient ingestion: Postprandial metabolismThe relationship between postprandial metabolism and cognitive behaviour after macronutrient ingestion is only marginally characterised, and outcomes are not conclusive. Furthermore, there is little understanding of how the multitude of postprandial metabolic changes affect simple and complex cognitive functions as well as different mood states (for review, see Bellisle et al. 1998).The inconsistent results regarding macronutrient ingestion and cognitive behaviour can mainly be explained by methodological differences, such as consideration of baseline values or differences in time intervals of postprandial measurements, as well as by the difficulty in defining and differentiating indices to study. In most studies mixed meals high in one macronutrient were tested instead of pure macronutrient preparations, and interactions between macronutrients were not considered. Observed effects can not therefore be related unambiguously to a single macronutrient. Furthermore, the complex meals usually differed in energy content, volume and sensory properties (e.g. taste, pleasantness, texture), which may all influence behaviour and mental performance (Craig, 1986; Rogers, 199...