Randomized Controlled Nutrition Trial on Reactive Hypoglycaemia on the Course of Memory and Attention Among Young Adults - Relevance of Chronotype

Studies in young adults indicate beneficial effects of a low-glycaemic index (GI) breakfast on cognitive performance. A meta-analysis of 17 studies revealed the benefits of a low-glycaemic (GL) load breakfast on immediate verbal memory only in the late postprandial period. No overall effect on attention in adults was reported, yet advantages for attention in children, adolescents, and young adults were suggested. Mechanisms explaining the time-dependent benefits of a low GL breakfast are not fully understood. The provision of glucose to the brain is currently discussed as a central mechanism linking meal GI/GL to cognition. Glucose is required for cognitive efforts as evidenced by decreases in local extracellular glucose concentrations in the activated brain area. Key neurotransmitter synthesis in the brain needs glucose. Glucose metabolism may influence memory through tryptophan utilization and serotonin concentrations. The memory-enhancing effect of glucose may require relatively constant blood glucose levels in the brain rather than high glucose amounts per se. Hence, whilst high GI foods elicit a transient increase in blood glucose levels, low-GI foods will result in a more sustained and longer-lasting provision of glucose. The late postprandial phase, when cognitive benefits of low GI/GL meals are most noticeable, coincides with the time after reactive hypoglycaemia following a high-GI meal. To disentangle the effects of dietary GI and reactive hypoglycaemia, it is prudent to examine beverages like fruit juices - characterized by a low GI, yet known to induce reactive hypoglycaemia even earlier postprandially. Accordingly, also detrimental effects on cognition should manifest earlier as observed for high-GI breakfast. Since recent work suggests that there may be an optimal blood glucose range for cognitive performance and that this optimal range may differ by cognitive domain, continuous glucose monitoring should be used in addition to the conventional measurement points directly before the cognitive test. However, benefits of low GI/GL breakfast for cognitive function have also been observed without differences in blood glucose levels. This may be attributable to an acutely improved postprandial insulin sensitivity and/or lower cortisol levels elicited by low-GI meals. Accordingly, concomitant examinations of all three factors, i.e. glucose, insulin and cortisol levels seem necessary to disentangle potential mechanisms. The above-mentioned meta-analysis also found greater benefits for individuals with better glucose tolerance, although age may confound this. Studies suggest that young adults with poorer glucose tolerance, even within the healthy range, may be more vulnerable to these effects. While glucose tolerance follows a circadian rhythm, being lowest in the evening due to reduced pancreatic β-cell function and insulin response, circadian misalignment-common among young adults with later chronotypes-can also impair glucose tolerance, even at breakfast, due to decreased insulin sensitivity. This misalignment, often caused by social jetlag, has been linked to obesity, type 2 diabetes, higher blood glucose, HbA1c levels, and an increased risk of depression. It remains unclear whether persons with later chronotypes are more susceptible to reactive hypoglycaemia after breakfast.

Hypothesis

1. Reactive hypoglycaemia in response to a low-GI beverage impairs memory and attention after approx. 90 minutes
2. Reactive hypoglycaemia after the consumption of low-GI beverage is more pronounced in healthy persons with a later chronotype
3. The adverse effect of a low-GI breakfast inducing reactive hypoglycaemia on memory and attention is particularly evident in those with later chronotype Aim This nutrition trial aims to investigate how low-GI beverages induce reactive hypoglycaemia and its effects on memory and attention after meals in postprandial phase. The investigators aim to explore the effects of chronotype in two student samples: those with earlier and later chronotypes. Further, the study investigate the relevance of chronotype for the postprandial course of glucose (including the occurrence of reactive hypoglycaemias), insulin and cortisol levels.

Methodology

Participants Healthy, German-speaking students at Paderborn University (early or late chronotype)