Abstract
Background: Optimal cognitive performance is important for learning. The brain uses glucose for fuel, so one proposed factor influencing cognition is circulating blood glucose concentrations. However, the existing body of literature on this topic is equivocal; possibly because foods and beverages used to generate differences in glycaemia, also differ in other attributes, such as fibre or macronutrient content. Some of these uncontrolled factors are found to influence glycaemia and cognition; therefore, they do not allow for any effects to be attributed solely to differences in glycaemia. More work is needed to control for confounding to clarify the relationship between cognitive performance and circulating blood glucose concentrations.
Objective: To investigate healthy adults’ cognitive performance with different glycaemic responses induced by sucrose and isomaltulose: two disaccharides with identical monosaccharides, but different glycosidic bonds, resulting in differences in the rates of digestion and absorption between sugars.
Design: Randomised, double blinded, crossover, controlled trial.
Methods: To examine the cognitive effects of different glycaemic responses, a sucrose beverage was compared to an isomaltulose beverage. To match sweetness of the test beverages 0.035g of sucralose was added to the isomaltulose beverages. Healthy human nutrition students (n=70; mean age 21.9 years; mean body mass index 23.3 kg/m2) received the lower glycaemic index (GI) isomaltulose + sucralose test beverage (ISO) and higher GI sucrose test beverage (SUC) on separate occasions. Following beverage consumption cognitive performance was examined at 30, 80, 130, and 140 minutes. Participants viewed a film in 30-minute time slots, then answered 10 questions about the film, and underwent a 25-word recall test. At 140 minutes participants completed the Reitan’s Trail Making Part B test. The tests were designed to measure declarative memory (film recall); immediate recall (word recall) and executive function (Reitan’s Trail Making Part B). To determine the glycaemic response of the test beverages, a subsample (n=12) from the cognitive testing population (n=70) underwent glycaemic response testing on separate days to the cognitive test days. The glycaemic response test protocol used the same beverages and timing protocol as the cognitive testing days.
Results: Between test beverages a significantly lower (mean difference (95% confidence interval) (CI) blood glucose iAUC concentration was found -44 (-70, -18) mmol/L∙min (p=0.003 for ISO compared to SUC). There was no significant difference between test beverages in the sum of correct answers to the film recall (declarative memory) at 30 min 0.1 (-0.2, 0.5), 80 min -0.3 (-0.8, 0.2), and 130 min 0.0 (-0.5, 0.5). Nor were any significant differences found in the amount of words recalled in the word recall tests (immediate recall) at 30 min -0.5 (-1.4, 0.3), 80 min 0.4 (-0.4, 1.3), and 130 min -0.4(-1.1, 0.4). At 140 minutes the times taken to complete the Reitan’s Trail Making Part B (executive function) was also not found to be significantly different -0.3(-6.9, 6.3).
Conclusion: Declarative memory, immediate free recall, and executive functions were not significantly different between different postprandial glycaemic responses. Our findings do not support the theory that cognitive test outcomes examined in this study will vary with different glycaemic responses.