Bone mass and soy isoflavones in socially housed, premenopausal macaques

Abstract

Background: Soy consumption is associated with a lower incidence of hip fracture in Asian than in Western women, an effect often attributed to estrogen-like compounds (isoflavones) in soy. It is not known whether premenopausal soy exposure initiated in adulthood can increase bone mass and thereby reduce fracture risk.Objective: We aimed to determine whether a high-isoflavone soy diet influences bone mass in soy-naïve, premenopausal cynomolgus monkeys (Macaca fascicularis).Design: Ninety-four skeletally mature females were randomly assigned to consume diets whose protein content came from either high-isoflavone soy or casein and lactalbumin. Animals were socially housed. Bone mass and circulating isoflavone concentrations were measured at baseline and 19 and 31 mo after the start of treatment; bone biomarkers were measured at baseline and 31 mo.Results: There were no significant differences at any timepoint in whole-body bone mineral content between casein-fed (112.5 ± 2.1, 119.2 ± 1.9, and 120.7 ± 2.1 g) and soy-fed (117.2 ± 2.1, 122.4 ± 2.0, and 125.4 ± 2.3 g; P = 0.12) monkeys. Similar results were seen for spinal bone mineral density (casein-fed: 0.46 ± 0.01, 0.50 ± 0.01, and 0.52 ± 0.01 g/cm2; soy-fed: 0.47 ± 0.01, 0.51 ± 0.01, and 0.52 ± 0.01 g/cm2; P = 0.30) and bone biomarker measurements—bone-specific alkaline phosphatase (soy-fed: 82.3 ± 4.1 and 63.2 ± 3.4 ng/mL; casein-fed: 94.1 ± 4.5 and 61.7 ± 4.3 ng/mL; P = 0.22) and C-terminal crosslink of type 1 collagen (soy-fed: 0.944 ± 0.06 and 0.89 ± 0.08 nmol/L; casein-fed: 0.97 ± 0.07 and 0.78 ± 0.06 nmol/L; P = 0.20).Conclusion: A soy diet high in isoflavones does not significantly affect bone characteristics in initially soy-naïve premenopausal monkeys.