Comparing the Effects of Dairy and Soybean on Bone Health in Women: A Food- and Component-Level Network Meta-Analysis

Background/Objectives: Dairy and soybean are important potential dietary sources of bone health. However, their comparative effectiveness and the role of specific components remain unclear. In this network meta-analysis (NMA), we aimed to compare the effects of various dairy and soy products (food level) and their key bioactive components (component level) on bone health in healthy women. Methods: We systematically searched PubMed, Embase, Cochrane Library, and Web of Science (up to 28 February 2025) for randomized controlled trials. A frequentist random-effects NMA was used to compare interventions for lumbar spine (LS) and total body (TB) bone mineral density (BMD) and bone turnover markers [osteocalcin (OC), deoxypyridinoline (DPD)]. Mean differences (MDs) and 95% confidence intervals were pooled. Interventions were ranked using the surface under the cumulative ranking curve (SUCRA). Results: Sixty RCTs involving 6284 participants (mean age: 54.2 years) were included. At the food level, no dairy or soy interventions significantly improved outcomes versus control, although milk + yogurt ranked numerically highest based on SUCRA values. At the bioactive-component level, the combination of casein + whey protein (MD 0.04 g/cm², 95% CI 0.01-0.06) and soybean protein (MD: 0.03 g/cm², 95% CI: 0.01-0.05) significantly increased TB BMD. Whey protein alone (SUCRA 74.4% for LS BMD) and casein + whey protein (SUCRA 86.3% for TB BMD and 75.9% for DPD) were among the highest-ranked interventions for bone health. Conclusions: The combination of milk and yogurt may be relatively promising among dairy products for bone health. Whey protein appears to be a key bioactive component beneficial for women's bone health.