Soy protein is beneficial but high-fat diet and voluntary running are detrimental to bone structure in mice

Authors: Yan, Lin; GRAEF, GEORGE - University Of Nebraska; Nielsen, Forrest - Frosty; JOHNSON, LUANN - University Of North Dakota; Cao, Jay

Submitted to: Nutrition Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2015
Publication Date: 6/1/2015
Publication URL: http://handle.nal.usda.gov/10113/61053
Citation: Yan, L., Graef, G.L., Nielsen, F.H., Johnson, L.K., Cao, J.J. 2015. Soy protein is beneficial but high-fat diet and voluntary running are detrimental to bone structure in mice. Nutrition Research. 35(6):523-531.

Interpretive Summary: Obesity is an excessive accumulation of body fat that adversely affects bone health in both humans and animals. Physical activity and dietary modification are two key approaches that may reduce the risk of obesity. We investigated the effects of voluntary running and soy protein consumption on bone health in mice fed a high-fat diet. Feeding mice a high-fat diet reduced bone volume and bone mineral density, indicating a detrimental effect on bone. Consumption of soy protein was beneficial to bone, evidenced by increases in bone volume and bone mineral density. Voluntary running reduced bone volume and bone mineral density compared to sedentary controls. These findings indicate that a high-fat diet has deleterious effects and consumption of soy protein has beneficial effects on bone health. The unfavorable effects of running on bone were unexpected. Voluntary running has been a useful tool for energy balance in animal models of obesity research. Further studies are needed to determine the optimal level of running activity that is the most appropriate to balance energy without adversely affecting bone health.

Technical Abstract: We investigated the effects of diet (AIN93G or high-fat), physical activity (sedentary or voluntary running) and protein source (casein or soy protein isolate) and their interactions on bone microstructural changes in distal femurs in male C57BL/6 mice by using micro-computed tomography. After 14 weeks of feeding, the high-fat diet reduced trabecular number (Tb.N, p < 0.01) and bone mineral density (BMD, p < 0.05) and increased trabecular separation (Tb.Sp, p < 0.01). Soy protein intake increased bone volume fraction (BV/TV), Tb.N, connective density (Conn.D) and BMD and decreased Tb.Sp (p < 0.01 for each variable). Running, at 4-8 km/d, decreased BV/TV, Tb.N, Conn.D (p < 0.01 for each variable) and BMD (p < 0.05) and increased Tb.Sp (p < 0.01). The high-fat diet reduced osteocalcin (p < 0.01) and increased tartrate-resistant acid phosphate 5b (TRAP 5b, p < 0.05) concentrations in plasma. Soy protein isolate elevated plasma concentration of osteocalcin (p < 0.01). Running increased plasma osteocalcin (p < 0.01) and reduced high-fat diet-induced increases in TRAP 5b (p < 0.05). These findings indicate that a high-fat diet has deleterious and SPI has beneficial effects on trabecular bone properties. The depression of trabecular structural characteristics by running suggests that there may be a maximal threshold of running capacity with mice, even on a voluntary basis, beyond which bone deterioration occurs. The significant elevation in plasma osteocalcin and reduction in TRAP 5b by running suggest that a compensatory bone formation may be counteracting the detrimental effects of excessive running.