Low back pain (LBP) is the leading cause of disability worldwide and is costly. Lifestyle factors, such as physical inactivity, stress, sleep, excess weight, and an unhealthy diet contribute to the burden of LBP and the associated increasing demand for care. Moreover, approximately 65% of LBP patients who visit the hospital are overweight. This group is considered a complex patient group. Of the LBP patients who visit the hospital, 74% are referred back to primary care as medical specialists cannot offer them high value care. Targeting both lifestyle factors (e.g., physical activity, sleep and stress) and clinical factors related to low back pain (e.g., muscle strength, endurance, mobility) is important in the management of this group of LBP patients to improve important outcomes (e.g., functioning, physical activity) and reduce costs. Addressing lifestyle factors may also offer additional health benefits like decreased risks of diabetes and cardiovascular diseases. The primary objective of this project is to improve the management of this complex group of LBP patients, that is, patients who are overweight or obese and who are referred back to primary care from the hospital because medical specialists cannot offer them high value care, and to reduce healthcare and societal costs. The primary research question is: 'Is a combined lifestyle intervention, integrated into standard care for LBP, delivered by physio/exercise therapists effective and cost-effective in improving physical functioning and/or physical activity over a 36-month period compared to usual care in overweight or obese LBP patients who are referred back from the hospital to primary care?' It is hypothesized that the combined lifestyle intervention, integrated into standard care for LBP, is both effective and cost-effective in managing LBP in patients who are overweight or obese over a 36-month period.