Chronic low back pain (CLBP) is the most expensive cause of workrelated disability: it causes the highest number of years lived with disability. The most severe and debilitated CLBP patients often have comorbidities such as overweight and obesity. Despite the growing body of scientific literature pointing towards the close interaction between overweight/obesity and CLBP, few treatment programs for people with CLBP nowadays take overweight into account. Therefore this study will examine the added value of a behavioral weight reduction program (changes in diet, behavior and physical exercise) to current best evidence rehabilitation (pain neuroscience education plus cognition-targeted exercise therapy) for overweight or obese people with CLBP. An international, multicenter randomized controlled trial comparing a behavioral weight reduction program combined with pain neuroscience education and cognition-targeted exercise therapy versus pain neuroscience education and cognition-targeted exercise therapy alone, will be conducted. The primary outcome is pain and the primary endpoint was chosen at 12 months follow-up; secondary outcomes include health care use and daily functioning (see detailed description of outcomes for an overview of all secondary outcomes). If the promising results of the proof of concept study are corroborated, the new intervention will have a high socio-economic impact, including an annual health care cost reduction of €66 million in Switzerland, and €60 million in Flanders, and is expected to increase life expectancy in the long term.

Rationale:

Chronic low back pain (CLBP) is the most common and important clinical, social, economic, and public health problem of all chronic pain disorders across the world. In addition to its high prevalence, CLBP is a severely disabling disorder characterized by tremendous personal and socioeconomic impact. Furthermore, it is the most common cause of work-related disability, generating long-term sick-leaves, and it causes the highest number of years lived with disability.

The most severe and debilitated CLBP patients often have comorbidities such as overweight and obesity. In fact, pain intensity and disability in people with CLBP show dose-responses to body mass index (BMI), waist circumference, percent fat and fat mass. Ample studies and several meta-analyses indeed confirm that overweight and obesity are associated with LBP, with overweight and obesity even being a risk factors for low back pain. Regarding socio-economic impact, overweight or obesity is not only related to LBP persistence, but also to higher rates of health care seeking for LBP. Obviously, people with CLBP who are overweight or obese, are likely to have more complex health needs requiring focus on lifestyle behavioral factors such as physical activity/exercise and diet.

CLBP is a complex disorder which is difficult to treat. Exercise therapy is an evidence-based treatment for CLBP both general exercises and cognition-targeted exercise therapy have shown beneficial effects on pain in patients with CLBP. Unfortunately, current treatments for CLBP apply a 'one-size-fits-all' approach and do not address comorbidities like obesity. This knowledge gap is now acknowledged internationally: overweight and obesity are increasingly recognized as a plausible therapeutic target for people with CLBP. Despite the growing body of scientific literature pointing towards the close interaction between overweight/obesity and CLBP few treatment programs for people with CLBP nowadays take overweight into account.

Few studies explored the added value of weight reduction to the management of people with CLBP. Yet, proof of concept for combining dietary changes with exercise therapy for patients with CLBP and comorbid overweight/obesity show promising results. Here we propose studying the added value of a behavioral weight reduction program (changes in diet, behavior, and physical exercise) to blended rehabilitation (PNE plus CTET) for overweight or obese people with CLBP. Both treatments are effective in their specific target population (i.e., behavioral weight reduction for overweight/obese people and PNE plus CTET for people with CLBP and normal BMI), but whether their combined approach is cumulative in overweight/obese people with CLBP is currently unknown and represents an important research priority.

Objectives:

The primary objective is to examine if a behavioral weight reduction program combined with Pain Neuroscience Education (PNE) and Cognition-Targeted Exercise Therapy (CTET) is superior to reduce pain at 12 months follow-up compared PNE and CTET alone, in overweight or obese people with CLBP.

Secondary objectives are to examine the effects of adding a behavioral weight reduction program combined with PNE and CTET, compared to PNE and CTET alone, on 1) other pain related outcomes (pain interference, pain distribution and pain beliefs), 2) on anthropometrics (body weight/composition, muscle thickness and fat distribution), 3) on energy balance related behavior (24h continuous activity monitoring, dietary intake and sleep) and finally 4) on health economics (heath care utilization, productivity loss and quality of life) at 12 months follow-up.

Interventions:

Both interventions (experimental and control) are organized equally: all participants will receive 18 treatment sessions over a 14-week period see table 2 for a detailed overview. Rather than practical, treatment arms will differ in content.

The control intervention will consist of a total of 18 treatment sessions distributed over 14 weeks. It comprises of only the chronic-pain-focused interventions: 3 sessions of PNE in the first 2 weeks & secondly, 15 sessions of CTET in the remaining 12 weeks.

The experimental intervention will consist of a total of 18 treatment sessions distributed over 14 weeks. The first part will consist of chronic-pain-focused interventions: firstly, 3 sessions of PNE in the first 2 weeks & secondly, 15 sessions of CTET in the remaining 12 weeks. The second part will consist of a more weight-reduction-focused intervention. The weight reduction intervention is a lifestyle approach that will be integrated in the CTET intervention, implying that grading daily physical activity and exercise levels will aim at reducing weight (i.e. together with a change in diet we aim at a caloric deficit of 500 to 700 kcal/day) and improving pain cognitions at the same time.

Study design:

Randomized controlled trial with follow-up assessments directly post-treatment (T1), 3 months post-treatment (T2), 6 months post-treatment (T3), 9 months post-treatment (T4) and 12 months post-treatment (T5).

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.

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