Submitted to: Applied Physiology, Nutrition & Metabolism
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2021
Publication Date: N/A
Interpretive Summary: A sedentary lifestyle is a risk factor for obesity, and obesity is associated with bone loss. Exercise reduces body fat mass and improves metabolism in obesity. We investigated the effect of voluntary running on bone quality in obese mice in a mouse model of diet-induced obesity. Compared to a control diet, the obesity-inducing diet increased body fat mass, decreased bone volume in the spine, and increased blood concentrations of TRAP 5b (a marker of bone resorption) in sedentary mice. On the other hand, voluntary running reduced body fat mass in mice with diet-induced obesity. Voluntary running had a greater effect on improving bone quality in long bone (for example, increased bone strength) than in the spine and decreased blood concentrations of TRAP 5b in obese mice. Findings from this study show that voluntary running improves bone quality by reducing bone resorption in obese mice.
Technical Abstract: Obesity increases the risk for pathological conditions such as bone loss. On the other hand, physical exercise reduces body adiposity. To test the hypothesis that physical activity improves bone quality, we evaluated voluntary running of defined distances on trabecular and cortical microstructure in mice fed a high-fat diet (HFD). Sedentary mice were fed the standard AIN93G diet or HFD. Mice fed the HFD remained sedentary or were assigned to unrestricted running or 75%, 50%, and 25% of unrestricted running with an average running activity at 8.3, 6.3, 4.2, and 2.1 km per day, respectively. The bone structural differences found in sedentary mice were that HFD, compared the AIN93G diet, resulted in a lower bone volume fraction (BV/TV) and a higher structure model index (SMI) in vertebrae. Running had a greater effect on trabecular microstructure in femurs than in vertebrae; the decrease in SMI and an increase in trabecular thickness (Tb.Th) were in a dose-dependent manner. Running was positively correlated with BV/TV and Tb.Th and inversely correlated with SMI in femurs. The HFD increased plasma concentrations of tartrate-resistant acid phosphatase 5b, a marker of bone resorption in sedentary mice; while running decreased it in a dose-dependent manner. The findings show that voluntary running improves bone quality in young adult mice fed an HFD.