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Background: Although mounting evidence indicates that insulin resistance (IR) co‐occurs with mitochondrial dysfunction in skeletal muscle, there is no clear causal link between mitochondrial dysfunction and IR pathogenesis. In this study, the exact role of mitochondria in IR development was determined. Methods: Six‐week‐old C57BL/6 mice were fed a high‐fat diet for 2 weeks to induce acute IR or for 24 weeks to induce chronic IR (n = 8 per group). To characterize mitochondrial function, we measured citrate synthase activity, ATP content, mitochondrial DNA (mtDNA) content, and oxygen consumption rate in gastrocnemius and liver tissues. We intraperitoneally administered mitochondrial division inhibitor 1 (mdivi‐1) to mice with acute IR and measured mitochondrial adaptive responses such as mitophagy, mitochondrial unfolded protein response (UPRmt), and oxidative stress (n = 6 per group). Results: Acute IR occurred coincidently with impaired mitochondrial function, including reduced citrate synthase activity (−37.8%, P < 0.01), ATP production (−88.0%, P < 0.01), mtDNA (−53.1%, P < 0.01), and mitochondrial respiration (−52.2% for maximal respiration, P < 0.05) in skeletal muscle but not in liver. Administration of mdivi‐1 attenuated IR development by increasing mitochondrial function (+58.5% for mtDNA content, P < 0.01; 4.06 ± 0.69 to 5.84 ± 0.95 pmol/min/mg for citrate synthase activity, P < 0.05; 13.06 ± 0.70 to 34.87 ± 0.70 pmol/min/g for maximal respiration, P < 0.001). Western blot analysis showed acute IR resulted in increased autophagy (mitophagy) and UPRmt induction in muscle tissue. This adaptive response was inhibited by mdivi‐1, which reduced the mitochondrial oxidative stress of skeletal muscle during acute IR. Conclusions: Acute IR induced mitochondrial oxidative stress that impaired mitochondrial function in skeletal muscle. Improving mitochondrial function has important potential for treating acute IR. [ABSTRACT FROM AUTHOR]

Osteopenia is a preclinical phase of osteoporosis, it occurs naturally with aging and increases the risk of bone fractures in elderly males. Previous studies have revealed the beneficial effects of soybean on preventing bone loss due to its isoflavone contents. Fermentation alters the soybean isoflavone contents, that is, isoflavone glucosides is hydrolyzed into aglycones. However, it is not clear how these alterations influences the preventive effect of soybean on bone loss. In this study, we fed senescence‐accelerated mouse prone 6 (SAMP6), a model of senile osteopenia, with an equal dosage of nonfermented soybean (NS) or fermented soybean, Doenjang (DJ) for 18 weeks. Mice supplemented with DJ showed 1.13‐fold higher bone densities and 1.06‐fold longer relative bone lengths than those of osteopenic SAMP6 mice old control (OC), while NS‐supplemented mice showed no significant improvement. Supplementation with DJ effectively prevented bone loss in the osteopenia model by the improvement of bone formation and reduction of osteoclastogenesis. In addition, we discovered that DJ increased osteogenesis in SAMP6 mice via BMP2‐Smad‐Runx2 signaling. These results suggest that the fermentation process could enhance bone loss prevention by soybean and dietary supplementation with fermented soybeans may be beneficial for bone health. Practical Application: Soybean fermentation improved the preventive effects of soybean on bone loss. Therefore, the consumption of fermented soybean, Doenjang, is a potential alternative for aging‐related bone loss therapy. [ABSTRACT FROM AUTHOR]