The ultimate aim of this project is to establish a validated strategy that allows for personalized intervention in adolescents (11 to 17 years) whom are assigned a state of overweight or obesity. The investigators will assess the following hypotheses: * Weight condition is reflected by the fecal metabolome (WP1) * Emotional stress is implicated in weight condition (WP1) * Functionality of the gut microbiome is related to the diet-stress-obesity axis (WP2) * Dietary pattern impacts the fecal metabolome and gut microbiome (WP2) * Personalized dietary intervention outperforms generalized dietary approaches (WP3) Participants will: * Produce a saliva, stool and hair sample * Fill in questionnaires regarding mental health, medical health and demographic information * Fill in a food frequency questionnaire and a 24-hrecalls * Be measured (height, weight, fat% and waist circumference) The samples will be analyzed using a technique called metabolomics to identify biomarker candidates with diagnostic and/or prognostic potential. Additionally, microbiome analysis will be performed to map the microbiome of all groups.