Effects of Milk or Yogurt Supplementation on Bone Health, Body Composition, and Gut Microbiota in Canadian Young Adults: Protocol for a Three-Arm Parallel-Group Randomized Controlled Trial (Preprint)

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BACKGROUND Osteoporosis is a major global public health concern, and optimizing peak bone mass during young adulthood is a main preventive strategy for reducing fracture risk later in life. Dairy foods, including milk and yogurt, provide nutrients, including calcium and protein, that support bone health. However, their long-term comparative effects on bone, body composition, and the gut microbiome in Canadian young adults are unknown. OBJECTIVE This study aims to evaluate the effects of two-year supplementation with fermented (yogurt) and non-fermented (milk) dairy products, compared to a habitual diet, on femoral neck bone mineral density (BMD) in Canadian adults aged 19 to 30 years. Secondary objectives include changes in BMD at other skeletal sites, including the total hip, lumbar spine, and whole body, as well as body composition, hormonal and bone turnover markers, gut microbiota composition and diversity following the intervention. METHODS The Fermented-Non-Fermented-Dairy (FNFD) trial is a two-year, prospective, randomized, three-arm, parallel-group controlled trial. In this study, 120 eligible healthy adults aged 19-30 years living in Saska-toon, Canada, with calcium intake <800 mg/day were randomized to one of three arms: 1) milk (375 mL) with habitual diet, 2) yogurt (350 g) with habitual diet, or 3) control (habitual diet). Data is collected at five time points; baseline, month 6, month 12, month 18, and month 24. The primary outcome is the change in femoral neck BMD. Secondary outcomes include BMD at other skeletal sites (total hip, lumbar spine, whole body), BMC (total hip, femoral neck, lumbar spine, whole body), bone structure and geometry, biochemical markers of bone turnover (osteocalcin, bone-specific alkaline phosphatase (BALP), C-terminal telopeptide of type 1 collagen (CTx-1), transforming growth factor-beta 1 (TGF-β1), TGF-β2, TGF-β3, and TGF-β receptor II (TGF-β RII), hormonal markers related to bone metabolism (parathyroid hormone (PTH), 25-hydroxyvitamin D [25(OH)D], and serum and salivary insulin-like growth factor-1 (IGF-1)), anthropometrics, body composition (total fat and lean mass), and gut microbiota. RESULTS Recruitment was conducted between July 2024 and July 2025, with an allocation ratio of 1:1:1 for the three study arms. All participants have completed all measurements until the month 6 time point, while month 12 follow-ups are ongoing. Month 24 assessments will take place from November 2026 to July 2027, followed by data analysis and dissemination through peer-reviewed publications and the trial registry. CONCLUSIONS This study uses a robust methodology and multidimensional outcome assessment to evaluate the effects of milk and yogurt supplementation on skeletal and metabolic health in young adults. The findings will contribute to evidence on dairy-based nutritional strategies to optimize long-term bone health in young Canadian adults. CLINICALTRIAL This trial is registered at ClinicalTrials.gov (Identifier: NCT06265246).

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