Postprandial Metabolism in Healthy Young Subjects

This study aims to describe the dynamic changes in nutritional biomarkers in the blood during the postprandial period, i.e. the time period from the last meal and into the fasting state. In total 36 healthy, young men and women will be recruited in Bergen, Norway, and after receiving a standardized breakfast meal they will consume only water for the next 24 hours.

Throughout the day, humans switch back and forth between the fed, postprandial (after a meal), and the postabsorptive (fasting) metabolic state. This is followed by a shift in fuel utilization from primarily using glucose to predominantly rely on β-oxidation of fatty acids. Consequently, circulating concentrations of biomarkers may fluctuate in response to this changing metabolic state. Much is known about the hormonal and metabolic effects of fasting, including lower insulin secretion, increased release of free fatty acids from adipose tissue, increased ketogenesis, glycogen breakdown, and activated gluconeogenesis. However, less is known about the effect on other biochemical markers in the postabsorptive period.

When evaluating nutritional biomarkers, both in clinical practice and in research, it is common practice to distinguish between fasting or non-fasting blood samples, based on time since the last meal. The extent to which different biomarkers are influenced by fasting status vary, and accordingly, several diagnostic cutoffs, e.g. plasma glucose for diabetes diagnosis, vary according to whether the sample was fasting or not. However, as the adaptation to fasting is a gradual process, it is expected that any changes in biomarker concentrations are also gradual. Further, as circulating metabolite concentrations are determined as a result of input (intestinal absorption and release from tissues), metabolism, and removal (utilization, storage, and excretion), we cannot reasonably assume that these changes are linear.

A few previous studies have aimed at describing the dynamics of fasting metabolism, demonstrating that the circulating metabolome changes during prolonged fasting in a dynamic manner. However, as data collection started after an overnight fast period, these studies do not provide data on the initial postprandial period and the adaptation to the fasting state. This study will extend the knowledge on the dynamics of human postprandial metabolism, by monitoring circulating concentrations of biomarkers during the 24 hours after a standardized breakfast meal. The investigators aim to capture the adaptation period from the fed to the fasting state and provide time-resolved data on a broad range of nutritional biomarkers.

Enrolled participants will attend the study center after an overnight fast, following a standardized evening meal consumed 12 hours before attendance. Anthropometric measurements (body weight, height, waist circumference, and body composition) will be taken in the fasting state, and a fasting blood sample will be drawn. After completing a standardized breakfast meal, the participants will remain at the study center for 12 hours, and blood will be frequently collected at specified time points. The participants will return to the study center the following morning for a final 24h fasting blood sample.

Eligibility Criteria:
Inclusion Criteria:

* Body Mass Index between 22-27 kg/m\^2
* No significant weight change (\>5%) during the last 3 months before the study visit
* Female participants should use one of the following oral contraceptives: Almina, Loette, Melleva, Microgynon, Mirabella, or Oralcon

Exclusion Criteria:

* Acute or chronic disease such as diabetes, thyroid diseases, cancer, cardiovascular disease, or inflammatory bowel disease, during the last 3 years
* Celiac disease or other food allergies interfering with the standardized breakfast meal
* Use of any prescription medications
* Smoking or regular use of other nicotine-containing products
* Pregnancy or breastfeeding the last 3 months