This study investigates short-term intra- and inter-individual variability in human blood metabolism under real-life conditions. Using minimally invasive finger-prick blood sampling, dietary records, and wearable devices, we will longitudinally monitor blood-circulating metabolites and glucose levels in healthy individuals over a four-week period without dietary or lifestyle intervention. The study focuses on metabolic transitions between pre- and postprandial states during habitual daily activities and routine meals. Mass spectrometry-based metabolomics will be used to characterize metabolite profiles and their associations with diet, physical activity, sleep, and stress. In parallel, the study evaluates the feasibility of microsampling approaches, wearable-derived physiological data, and isotope-labelled standards for robust and cost-effective metabolite quantification. The results will inform the design of larger longitudinal studies using minimally invasive blood sampling in non-controlled settings.

Human metabolism is highly dynamic and continuously influenced by food intake, physical activity, sleep, stress, and other routine physiological factors. Following meal consumption, individuals enter a postprandial metabolic phase characterized by digestion, absorption, and metabolic handling of ingested nutrients. The magnitude and duration of postprandial metabolic responses vary substantially within and between individuals and reflect the individual capacity to maintain metabolic homeostasis. Although many metabolomics studies rely on controlled diets and fasting conditions to reduce variability, most individuals in Western societies spend the majority of their daily lives in a non-fasted, fed state. Therefore, understanding metabolic variability under routine, non-controlled conditions is essential for a more comprehensive characterization of human metabolism.

This pilot study aims to investigate short-term intra- and inter-individual variation in blood-circulating metabolites under real-life conditions. Healthy participants will be followed longitudinally over a four-week period without dietary or lifestyle intervention. Minimally invasive finger-prick blood sampling will be combined with dietary records and wearable devices to collect repeated metabolic and physiological measurements during habitual daily activities.

Blood glucose levels will be measured to capture postprandial responses, and finger-prick blood samples will be collected for mass spectrometry-based metabolomics analysis. Metabolite profiles will be examined in relation to recorded dietary intake, physical activity, sleep patterns, and self-reported stress levels. In addition to characterizing metabolic variability, the study will evaluate the feasibility of microsampling strategies and the integration of metabolomics data with wearable-derived physiological measures. From an analytical perspective, isotope-labelled standards will be applied to support robust and cost-effective quantification of circulating metabolites.

Overall, this study aims to generate methodological and biological variation insights that explore personalize metabolism and support the design of larger medium- and long-term longitudinal studies using minimally invasive blood sampling in non-controlled, real-world settings.

Inclusion Criteria:

1. Age: 18-65 years old
2. Body Mass Index (BMI): 18.5-29.9 kg/m2
3. Weight stability within the previous 3 months (self-reported).
4. Positive intention to maintain usual routine physical activity and eating habits during the study.

Exclusion Criteria:

1. Presence of acute chronic diseases, inflammatory or functional gastrointestinal disorders, or any diagnosed disease condition that disrupt daily routine activities.
2. Routine use medications or supplements that could potentially interfere with the study outcomes
3. History of eating disorder
4. Recent use of antibiotic medication within the last 3 months prior to the first visit
5. Active efforts to lose weight
6. Smoking
7. Consumption of alcoholic drinks exceeding nine standard cups per week and/or more than three standard cups per occasion