Soy Isoflavones Prevent Bone Quality Loss Induced by High‐Fat Diet in Rats Through Epigenetic Modifications

Chronic consumption of a Western-style diet, high in saturated fats and cholesterol, disrupts energy metabolism, leading to obesity and insulin resistance. In contrast, isoflavone (Isof)-rich soy has been shown to benefit connective tissue metabolism. However, the potential of soy Isof dietary supplementation to counteract the effects of a high-fat diet (HFD) on bone development, morphology, and remodeling remains poorly understood. In this study, 24-day-old male Sprague-Dawley rats were fed a HFD containing 45% fat and 0.25% cholesterol for 8 weeks, leading to significant increases in body weight, long bone length, bone marrow adiposity, and insulin resistance when compared to control diet (AIN-93G) rats. Using micro-CT and three-point bending tests, we found that supplementation of HFD with dietary soy Isof (NovasoyR 400: 352 mg Isof/g; Genistein, Daidzein, Glycitein ratio of 1.3:1:0.15 identical to that found in soybeans) prevented HFD-induced reductions in bone mass, including bone volume, trabecular number, density, and strength. These bone-preserving effects were associated with decreased non-esterified free fatty acid (NEFA) levels and increased alkaline phosphatase activity in serum and bone marrow plasma. Isof supplementation also ameliorated HFD-induced increases in the expression of Ezh2 and H3k27me3 levels (gene silencing epigenetic mark catalyzed by Ezh2) in bone and blocked the elevated expression of osteoclastic marker NFATc1 in bone marrow cells. A significant inverse correlation between bone mineral density (BMD) and DNA methylation marker 5-methylcytosine (%5-mC), as well as a positive correlation between serum NEFA levels and Ezh2 expression, were observed. Furthermore, Isof supplementation inhibited HFD-induced increases in bone DNA methylation. These results suggest that: (1) HFD disrupts bone and adipose tissue development and remodeling in post-weanling juvenile rat models; (2) Isofs may protect against high-fat diet-induced bone impairments. We hypothesize that the molecular mechanisms underlying Isof's bone protective effects may involve modulation of histone and DNA methylation through regulation of Ezh2 levels.