Soy protein supplementation in men following radical prostatectomy: a 2-year randomized, placebo-controlled clinical trial.

2021-04
The American journal of clinical nutrition 113(4)
- Maarten C Bosland
- Erika Enk
- Joanne Schmoll
- Michael J Schlicht
- Carla Randolph
- Ryan J Deaton
- Hui Xie
- Anne Zeleniuch-Jacquotte
- Ikuko Kato

PubMed: 33564828
DOI: 10.1093/ajcn/nqaa390

Study Design

Type: Randomized Controlled Trial (RCT)
Sample size: n = 50
Population: 44- to 75-y-old men who were at risk of cancer recurrence following prostatectomy randomized to soy (n = 50) or a casein-based placebo (n = 43)
Methods: Randomized controlled trial of dietary supplementation with 20 g/d soy protein isolate, providing 41 mg/d total isoflavones and 23 mg/d genistein
Blinding: Open-label
Duration: 2 y
Funding: Unclear

Background

Many studies have addressed effects of dietary supplementation with soy protein, but most have been inconsistent and few have been long-term studies in men.

Objectives

This study was a secondary analysis of body weight, blood pressure, thyroid hormones, iron status, and clinical chemistry in a 2-y trial of soy protein supplementation in middle-aged to older men.

Methods

Data were analyzed 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 44- to 75-y-old men who were at risk of cancer recurrence following prostatectomy randomized to soy (n = 50) or a casein-based placebo (n = 43). Weight, blood pressure, and blood samples were collected at baseline, every 2 mo in year 1, and every 3 mo in year 2.

Results

Compared with casein, soy supplementation did not affect body weight, blood pressure, serum total cholesterol, calcium, phosphorus, and thyroid hormones. Serum ferritin concentrations doubled over 2 y in both groups (117-129%), whereas hemoglobin and hematocrit increased slightly. In an exploratory subgroup analysis of soy group data, weight increased in subjects producing equol but not in nonproducers. Blood pressure was reduced in nonequol producers but not in producers. Other endpoints were not affected by equol production status.

Conclusions

Soy protein supplementation for 2 y compared with a casein-based placebo did not affect body weight, blood pressure, serum total cholesterol, iron status parameters, calcium, phosphorus, and thyroid hormones. Exploratory analysis suggests that equol production status of subjects on soy may modify effects of soy on body weight and possibly blood pressure. This trial was registered at clinicaltrials.gov as NCT00765479.

Research Insights

Soy Protein→Increased Hemoglobin Levels
Serum ferritin concentrations doubled over 2 y in both groups (117-129%), whereas hemoglobin and hematocrit increased slightly.
Effect
Neutral
Effect size
Small
Dose
20 g/day providing 41 mg/day total isoflavones and 23 mg/day genistein
Soy Protein→Reduced Blood Cholesterol
Compared with casein, soy supplementation did not affect body weight, blood pressure, serum total cholesterol, calcium, phosphorus, and thyroid hormones.
Effect
Neutral
Effect size
Small
Dose
20 g/day providing 41 mg/day total isoflavones and 23 mg/day genistein
Soy Protein→Reduced Blood Pressure
Compared with casein, soy supplementation did not affect body weight, blood pressure
Effect
Neutral
Effect size
Small
Dose
20 g/day
Soy Protein→Reduced Body Weight
Compared with casein, soy supplementation did not affect body weight
Effect
Neutral
Effect size
Small
Dose
20 g/day
Soy Protein→Reduced Calcium Level
Compared with casein, soy supplementation did not affect body weight, blood pressure, serum total cholesterol, calcium, phosphorus, and thyroid hormones.
Effect
Neutral
Effect size
Small
Dose
20 g/day providing 41 mg/day total isoflavones and 23 mg/day genistein
Soy Protein→Reduced Ferritin Level
Serum ferritin concentrations doubled over 2 y in both groups (117-129%), whereas hemoglobin and hematocrit increased slightly.
Effect
Neutral
Effect size
Small
Dose
20 g/day providing 41 mg/day total isoflavones and 23 mg/day genistein
Soy Protein→Reduced Hematocrit
Serum ferritin concentrations doubled over 2 y in both groups (117-129%), whereas hemoglobin and hematocrit increased slightly.
Effect
Neutral
Effect size
Small
Dose
20 g/day providing 41 mg/day total isoflavones and 23 mg/day genistein
Soy Protein→Reduced Phosphorus Level
Compared with casein, soy supplementation did not affect body weight, blood pressure, serum total cholesterol, calcium, phosphorus, and thyroid hormones.
Effect
Neutral
Effect size
Small
Dose
20 g/day providing 41 mg/day total isoflavones and 23 mg/day genistein
Soy Protein→Reduced Serum Phosphorus Level
Compared with casein, soy supplementation did not affect ... calcium, phosphorus
Effect
Neutral
Effect size
Small
Dose
20 g/day
Soy Protein→Reduced Thyroid Hormone Level
Compared with casein, soy supplementation did not affect ... thyroid hormones
Effect
Neutral
Effect size
Small
Dose
20 g/day
Soy Protein→Reduced Total Cholesterol Levels
Compared with casein, soy supplementation did not affect ... serum total cholesterol
Effect
Neutral
Effect size
Small
Dose
20 g/day
Soy Protein→Reduced Uric Acid Levels
Compared with casein, soy supplementation did not affect ... calcium, phosphorus
Effect
Neutral
Effect size
Small
Dose
20 g/day