CHICAGO – Soy protein bars containing phytoestrogens raised borderline low serum total testosterone levels while improving cardiovascular risk factors and glycemic control in older type 2 diabetic men with compensated hypogonadism.
The randomized trial was conducted because of theoretic safety concerns surrounding consumption of soy supplements by this population. Soy contains phytoestrogens, natural estrogens that might have a testosterone-lowering effect that would be particularly unwelcome in older men with type 2 diabetes, because low testosterone is associated with increased cardiovascular risk.
Thus, there was the possibility that the established cardiovascular and type 2 diabetic preventive benefits of frequent soy intake might be negated by a concomitant testosterone-lowering effect in men already at increased cardiovascular risk with low testosterone, Dr. Thozhukat Sathyapalan explained at the joint meeting of the International Congress of Endocrinology and the Endocrine Society.
Those concerns were shown to be groundless in the 12-week, double-blind, randomized clinical trial, reported Dr. Sathyapalan, an endocrinologist at the University of Hull (U.K.).
The study included 210 men with type 2 diabetes aged 55-70 years with subclinical hypogonadism as defined by a serum total testosterone of 12 nmol/L or less but normal gonadotrophin levels. They were randomized to 3 months of daily consumption of two cereal bars, each containing 30 g of soy protein, with the bars eaten by one group containing 66 mg each of soy phytoestrogens, while the other group’s soy bars were phytoestrogen free. That level of soy phytoestrogen consumption – 132 mg/day – is equivalent to intake in a typical Asian diet.
Dr. Thozhukat Sathyapalan
The primary outcome was change in serum total testosterone over the course of 3 months. It rose in both groups. Diastolic blood pressure fell to a similar extent in both study arms, while systolic pressure was unchanged over time. Endothelial function as assessed by the reactive hyperemia index improved in the soy-plus-phytoestrogens group and worsened in the soy-only group. Improvements in multiple other markers of cardiovascular risk and glycemic control were restricted to the soy-with-phytoestrogens group. Body weight remained steady in both groups throughout the study period.
The study was funded by the U.K. Food Standards Agency, which regulates food safety. Dr. Sathyapalan reported having no financial conflicts.