Lifestyle Intervention in Overweight/Obese Chronic Low Back Pain (CLBP) Patients: an International Multi-center RCT

Inclusion Criteria: * Adults (18 - 65 years) * Overweight (BMI ≥ 25 kg/m2) or obese (BMI ≥ 30 kg/m2) women and men. * CLBP (n=252), which is defined as nonspecific low back pain for at least 3 months duration, currently seeking care for low back pain and leg pain not ≥ 7 (on a maximum of 10) on a numeric rating scale. * Continue usual care 6 weeks prior to (to obtain a steady stat) and during study participation. * Depending on the country of inclusion: Native Dutch speaker (for Belgium) or Native German speaker (for Switzerland). Exclusion Criteria: * Patients with BMI ≥ 40 kg/m² will be excluded as people being morbid obese are eligible to undergo abdominal surgery. Because BMI may not always correspond to the same body fat percentage in different individuals (e.g., athletic types with higher muscle mass may also have BMIs ≥ 25 km/kg²), each participant's body fat percentage will be measured using the TANITA and compared to the body fat percentage reference values. Participants with exceeding BMI but falling into the healthy fat percentage range (which is sex-, age- and ethnicity dependent will be excluded. * Pregnant, currently breastfeeding or given birth in preceding year. * Currently receiving dietary or exercise interventions or received in the past 6 weeks. * Show evidence of specific spinal pathology based on self-report (e.g., hernia, spi-nal stenosis, spondylolisthesis, infection, spinal fracture or malignancy), or a se-vere underlying comorbidity specific diagnoses that interfere with treatment (e.g., diagnosed diabetes, cardiovascular problems, metabolic diseases) * Other severe diseases based on current medication intake or being currently treated by a medical doctor for a specific diagnosis, (e.g. diagnosed eating disorders). * Ongoing problems or cases with insurance companies regarding their back.