Soy Foods and Oestradiol Levels in Males: What the Evidence Shows

Concerns about soy increasing oestrogen levels in men are common, yet population-based research suggests a very different story.

A landmark study by Nagata et al. (2000) examined the relationship between soy food consumption and circulating sex hormones in Japanese men, a population with traditionally high soy intake.

Study overview

• Design: Cross-sectional observational study

• Participants:  Adult Japanese men

• Dietary assessment:  Intake of traditional soy foods, including:

  • Tofu

  • Miso soup

  • Baked bean curd

  • Deep-fried tofu

• Outcome measures:  Serum oestradiol, testosterone, and androgen–oestrogen ratios

Key findings:

Men with higher consumption of soy foods showed:

• Lower circulating oestradiol levels

• A more favourable androgen-to-oestrogen balance

• No evidence of oestrogen excess or feminising effects

Importantly, the inverse association was seen with whole soy foods, not isolated supplements.

Why this matters

Soy contains isoflavones (genistein, daidzein), which act as selective oestrogen receptor modulators (SERMs) rather than as oestrogen mimics. In men, these compounds may:

• Compete with endogenous oestradiol at the oestrogen receptor

• Reduce aromatase activity

• Support healthier oestrogen metabolism

This helps explain why higher soy intake was associated with lower, not higher, oestradiol levels.

Important context

• This was an observational study, not an intervention trial

• Findings reflect dietary soy foods, not highly processed soy isolates

• Results align with broader epidemiological data from Asian populations

Practical takeaway

Traditional soy foods such as tofu, miso soup, and fermented soy products can be part of a balanced diet for men and do not appear to raise oestradiol levels.  In fact, they may contribute to healthier oestrogen regulation.

For men concerned about oestrogen dominance, the focus should remain on:

• Whole foods

• Dietary patterns

• Metabolic health

  
  

  —not on fear of traditional soy foods.

For a broader analysis of dietary influences on oestrogen dominance in men, see our recent systematic review in Human Nutrition & Metabolism. https://authors.elsevier.com/sd/article/S2666-1497(25)00058-1