GlyCoBrain Observation - Breakfast Habits Among Students With Early and Late Chronotype

Background Breakfast is commonly considered one of the most important meals of the days. Failure to consume a breakfast, i.e., breakfast skipping, has been related to an increased risk of overweight/obesity or type 2 diabetes in the longer-term, but may also adversely affect cognition and academic performance. Similarly, breakfasts with a high glycaemic index (GI) resulting in sharp rises in blood glucose may adversely affect memory and attention, particularly in the late postprandial phase (i.e., 120-180 minutes after breakfast). A recent meta-analysis suggests specific effects for immediate and delayed episodic memory among persons with a better glucose tolerance.

Whilst young adults generally have a better glucose tolerance they are, however, prone to circadian misalignment since their midpoint of sleep (i.e., chronotype) is most delayed. Chronotype is a biological construct mainly influenced by genetics, sex and age. Chronotype tends to shift later from adolescence into early adulthood with the peak of delay around age 20 before moving back to an earlier chronotype. Hence, persons in young adulthood are more likely to have a later chronotype and experience a circadian misalignment between the "inner clock" and social requirements. Such a desynchronization may lead to poorer glucose tolerance and an exaggerated glucose response to a high GI breakfast in individuals with a later chronotype. Our recent research suggests that persons with a later chronotype were similarly vulnerable to both very early and late high GI meals, whereas earlier chronotypes had lower glucose responses to the high GI meal consumed at breakfast. In addition, research from female twins suggests that timing of breakfast has a larger underlying genetic component than timing of dinner, suggesting that consumption of an early breakfast may present a burden for those with a later chronotype. As a result, the cognitive performance of people with a later chronotype could particularly benefit from consuming a low GI breakfast. Current studies also report that later chronotypes delay their meal timing, tend to skip breakfast, are at higher risk to consume larger meals at night than earlier chronotypes and to have less favourable dietary pattern, consuming less protein and vegetables and more sweets, sugar, alcohol and coffee.

Taken together, a later chronotype may make young adults more vulnerable to consume unfavourable breakfasts, i.e. breakfasts with a higher dietary GI, higher energy density and lower micronutrient adequacy. However, to date no study has investigated breakfast habits in relation to chronotype in young adults. Furthermore, it remains to be elucidated which food students choose to account for the necessity of academic performance in preparation for an exam in the morning.

The present study will examine the relevance of breakfast among students in detail and relate this to their chronotype. The observational study will be followed by two nutritional intervention studies only with the earliest and latest chronotypes to examine the effects of high GI breakfast or a breakfast causing a reactive hypoglycaemia on cognitive functions in the early morning.

Hypothesis The hypothesis of the GlyCoBrain observational study is that students with a later chronotype are more likely to consume breakfasts with a higher dietary GI, higher breakfast energy density and lower breakfast micronutrient adequacy. We also postulate that persons with a later chronotype are more prone to consume foods from higher GI sources in preparation for an exam than those with an earlier chronotype.