BackgroundLow back pain (LBP) is a major global health issue, affecting approximately two-thirds of the population at some point in their lives. Modic changes (MCs) in the vertebral endplates, as observed on MRI, are recognized contributors to LBP and may be linked to advanced stages of intervertebral disc degeneration (IDD). Prior research has shown a decrease in the genus Bifidobacterium in the endplate cartilage of patients with IDD and concurrent MCs. The potential link between reduced Bifidobacterium levels and MC-related LBP remains unclear.MethodsThis multicenter, double-blinded, randomized, placebo-controlled trial will be conducted at four hospitals in China, comparing the efficacy of orally administered Bifidobacterium adolescentis (BA) with that of a placebo. Participants will receive the treatment twice daily for a duration of three months. The study targets patients with chronic low back pain (LBP) and Modic type I or II. Eligible patients will be randomly assigned to receive either Bifidobacterium adolescentis or a placebo for three months. The primary outcome will be the change in the Simplified Chinese Roland-Morris Disability Questionnaire (SCRMDQ) score at 3, 6, and 12 months post-treatment. Secondary outcomes include changes in DASS-21 scores, MRI imaging, bone density measurements, and serum biomarker analysis.DiscussionThis study will provide valuable insights into the therapeutic potential of Bifidobacterium adolescentis in managing chronic LBP associated with Modic changes, potentially offering a novel approach to treating this common and debilitating condition.Trial registrationThe trial has been registered with China Clinical Trial Registry, under the registration number ChiCTR2400088577. Registered on 21 August. The study was prospectively registered.