Nutrition Trial on the Glycaemic Response to High GI Meals Consumed at Morning vs. Evening-The ChroNu Study

Several studies suggest that meal timing plays an important role in the development of obesity and metabolic diseases. Especially in the evening, a high consumption of carbohydrates, which greatly increase blood glucose levels (i.e. unfavourable carbohydrates with a higher glycaemic index (GI)), has been found to adversely affect glycaemic response. However, avoidance of (unfavourable) carbohydrate consumption appears to be particularly problematic for young adults due to its interference with the timing of social life and their chronotype. The chronotype describes individual differences in sleep timing on free days and is most delayed around the age of 20. Young adults are thus prone to be exposed to a dietary misalignment when socially determined schedules, such as early lectures at universities, collide with their biologically determined later chronotype.

Therefore, it is hypothesized that dietary misalignment among young adults has detrimental short-term effects on the glucose metabolism.

In this nutrition trial, dietary misalignment is induced by providing the same meal rich in carbohydrates with a high glycaemic index (GI) on two separate days at different times: breakfast at 7:00 is assumed to reflect a schedule potentially inducing dietary misalignment among later chronotypes. Vice versa, providing this meal at dinner (20:00) may cause dietary misalignment among earlier chronotypes.

Adverse glycaemic responses are expected when the high GI meal is consumed at a time which is deviating from the schedule of the individual chronotype. A regular increase in postprandial glycaemia due to constant dietary misalignment may be important in the development of metabolic diseases.

To address the hypothesis that dietary misalignment among young adults has detrimental short-term effects on glucose metabolism, participants will consume a meal rich in high GI carbohydrates on two separate days either at breakfast (7:00) or at dinner (20:00). Glycaemic responses will be monitored by a continuous glucose monitoring device (CGM) (G6, Dexcom, Inc., San Diego, CA). The CGM electrochemically measures subcutaneous interstitial glucose concentrations of each participant during the whole study. A blood glucose meter will be used to verify the functionality of the CGM (CONTOUR®NEXT ONE).

The caloric content of the meals will be tailored to the energy needs of the participants based on their age, sex and anthropometric measurements. Participants will be requested to consume the meals without any break. During the controlled nutrition trial, participants will be asked to abstain from alcohol consumption and heavy exercise and not consume any food in addition to that provided or drinks that should be explicitly avoided.

To objectively corroborate their chronotype participants will be asked to wear an accelerometer (E4 wristband, Empatica) attached to the wrist during the controlled nutrition trial. Moreover, participants are asked to record their bed times, meal timings, daily routines, and physical activities during the trial. On day 1 and day 8, anthropometric measurements will be performed to compare the body composition (Bioimpedance Analysis, SECA mBCA) before and after the controlled nutrition trial. On day 4, fasting blood samples will be collected. Before the controlled nutrition trial will start, questionnaires on daily routines, food frequency, and chronotype will be carried out.

The chronotype is defined as mid-sleep point and assessed by the Munich Chronotype Questionnaire, which is a validated questionnaire. Earlier and later chronotypes will be defined as 20% of the participants with each the earliest and later mid-sleep points among the participants of the ChroNu cohort.

Eligibility Criteria:
Inclusion Criteria:

* Healthy students of Paderborn University
* 18 - 25 years old at time of screening for the ChroNu cohort
* 18,5 kg/m² \< BMI \> 30 kg/m²
* Free of diseases requiring constant or chronic medical treatment (except for oral contraceptives)
* Willingness to participate in the nutrition trial (8 days) including invasive measurements
* Fluent knowledge of the German language

Exclusion Criteria:

* students studying nutrition science at the University Paderborn
* regular smokers
* pregnancy or lactation
* chronic diseases: diabetes mellitus (all types), pre-diabetes, individuals with bleeding disorders (thrombocytopenia, haemophilia)
* contact dermatitis to adhesive plaster or skin disease that prevents the participant from wearing the CGM
* intake of medication which influence the chronotype: such as antidepressants or sleeping pills
* shift work in the past 3 months
* crossing of \> 1-time zone in the past 3 months
* strict vegetarians /vegans
* individuals having an allergy or intolerance to food that is included in the diet