Acute cognitive effects of different glycaemic responses in healthy adults

Background: The primary fuel for the brain is glucose derived from the systemic circulation. This has led to the hypothesis that blood glucose concentration can influence cognitive performance. However, the existing literature is inconsistent, which may be caused not only by the heterogeneity in study designs but by uncontrolled confounding factors. More work with better control of confounding is warranted. Objective: To compare the effects of different glycaemic responses, induced by beverages with different energy contents (sucrose and sucralose) and beverages with different glycaemic index (GI) (sucrose and isomaltulose) on memory and attention in healthy adults. Design: Randomized, double-blinded, crossover, controlled trial. Methods: A sensory test (n=11) was conducted to match the sweetness of sucrose and sucralose drinks. Glycaemic responses to sucrose and isomaltulose ingestion were measured (n=12; mean age 28.4 years; mean body mass index 23.5 kg/m2) on separate days to the cognitive test days. Participants (n=55; mean age 25.5 years; mean body mass index 22.0 kg/m2) received sucrose (50g), isomaltulose (50g) and sucralose (120mg) drinks after an overnight fast on separate occasions with at least one-week interval. The Complex Figure test, the Word Recall test, the Trail Making Test Part B, and the Stroop test were administrated 60 minutes after beverage ingestion. These tests were designed to measure verbal memory (Word Recall test), visual memory (Complex Figure test), and attention (Trail Making Test Part B and Stroop test). Results: Sensory tests indicated that the sweetness of the beverages were indistinguishable. Plasma glucose concentration 30 minutes after ingestion was significantly different between the sucrose and isomaltulose group (8.5 vs 6.4mmol/L, with a mean (95% CI) difference of 2.1 (1.1, 3.1) mmol/L). Comparing between a noncaloric (sucralose) and a caloric sweetener (sucrose), there were no significant differences in the mean (95% CI) for the following: Complex Figure test: immediate recall -0.37 (-1.44, 0.70), delayed recall -0.47 (-1.53, 0.60); Word Recall test: immediate recall 0.28 (-0.66, 1.22), delayed recall 0.30 (-0.63, 1.22); Trail Making Test Part B: completing time -2.10 (-7.26, 3.05) seconds; Stroop test: number of correct congruent responses 0.11 (-0.08, 0.30) and correct incongruent responses 0.21 (-0.47, 0.90), time used for correct congruent responses -3.63 (-26.79, 19.53) milliseconds and correct incongruent responses -7.19 (-32.01, 17.64) milliseconds. Comparing between a low GI (isomaltulose) and a medium GI sweetener (sucrose), there were no significant differences in the mean (95% CI) for the following: Complex Figure Test: immediate recall -0.81 (-1.90, 0.28), delayed recall -0.96 (-2.04, 0.11); Word Recall Test: immediate recall 0.28 (-0.67, 1.23), delayed recall 0.59 (-0.34, 1.53); Trail Making Test Part B: completing time -2.31 (-7.51, 2.89) seconds; Stroop test: number of correct congruent responses 0.04 (-0.15, 0.23) and correct incongruent responses 0.28 (-0.42, 0.97), time used for correct congruent responses -10.84 (-34.30, 12.62) milliseconds and correct incongruent responses -18.34 (-43.49, 6.80) milliseconds. Conclusion: This study does not support the proposition that cognitive outcomes will be affected by differences in postprandial glycaemic responses