Is soy protein supplementation beneficial in men after prostatectomy?

Two-year supplementation with soy protein appears to have no significant impact on body weight, blood pressure, serum total cholesterol, iron status parameters, calcium, phosphorus, and thyroid hormones compared with a casein-based placebo, a study has found.

Furthermore, “[e]xploratory analysis suggests that equol production status of [individuals] on soy may modify effects of soy on body weight and possibly blood pressure,” the investigators said.

In this study, data were analysed as secondary outcomes of a randomized controlled trial of dietary supplementation with 20 g/d soy protein isolate, providing 41 mg/d total isoflavones and 23 mg/d genistein, in middle-aged to older men (aged 44–75 years) who were at risk of cancer recurrence following prostatectomy and randomized to soy (n=50) or a casein-based placebo (n=43).

In addition, the investigators collected blood samples, blood pressure, and weight at baseline, every 2 mo in year 1, and every 3 mo in year 2.

Soy supplementation showed no impact on body weight, blood pressure, serum total cholesterol, calcium, phosphorus, and thyroid hormones relative to casein. At year 2, serum ferritin concentrations doubled in both groups (117–129 percent), while haemoglobin and haematocrit increased slightly.

An exploratory subgroup analysis of soy group data revealed an increase in weight among individuals producing equol but not in nonproducers. Blood pressure decreased in nonequol producers but not in producers. Equol production status did not affect other endpoints.