The high prevalence and treatment resistance of obesity urges further exploration into early diagnosis and prevention. This is especially important at young age, when metabolic and psychological development are ongoing. Psychological factors like stress can favor obesity, but researchers still struggle with the complex processes towards disease susceptibility. This project aims to elucidate pathways and identify potential clinical biomarkers in the stress-obesity relation via salivary metabolomics on two ongoing observational population-based studies in adolescents (OPERA n=140, 6-16y and Fin-HIT n=11000, 9-12y). Saliva can be non-invasively collected while its metabolic composition parallels that of blood. Hence, the associations between the metabolome from different matrices (plasma, feces, saliva) in the stress-obesity axis will be investigated using state-of-the-art high-resolution mass spectrometry. Studying metabolome differences between subgroups (low/high stress and healthy/overweight; including change over time) will explain why not all high stress adolescents develop obesity and why not all obese adolescents develop stress. Finally, potential salivary metabolite markers will be compared with existing clinical biomarkers of underlying pathways like stress physiology, appetite, energy balance, inflammation and microbial metabolites, thereby proving its potential as alternative clinical matrix and filling the gaps in our understanding of the stress-obesity axis.