Men with type 2 diabetes often struggle with low testosterone, inflammation, and increased cardiovascular risk. A clinical trial published in the Journal of Clinical Endocrinology & Metabolism explored whether soy protein—with or without isoflavones—could improve hormone levels, blood sugar control, and heart‑related markers in this population.

The results were surprising: soy isoflavones did not lower testosterone, but they did improve several important metabolic and cardiovascular markers.

What the researchers wanted to understand

The study examined whether soy protein, especially when combined with isoflavones, could:

• affect testosterone levels in men with subclinical hypogonadism
• improve blood sugar control
• reduce inflammation
• improve cardiovascular risk markers

Two groups of men consumed soy daily for three months:

• SPI: soy protein with 66 mg/day of isoflavones
• SP: soy protein without isoflavones

What the study found

• No change in testosterone. Neither soy group experienced increases or decreases in total or free testosterone.
• Better blood sugar control with isoflavones. The SPI group showed improvements in:
  • HbA1c
  • fasting glucose
  • fasting insulin
  • insulin resistance (HOMA‑IR)
• Reduced inflammation. C‑reactive protein (CRP) decreased significantly in the SPI group.
• Improved cardiovascular markers. Men taking soy with isoflavones showed:
  • lower triglycerides
  • lower diastolic blood pressure
  • better endothelial function
  • a 6% reduction in estimated 10‑year coronary heart disease risk
• Thyroid changes occurred. The SPI group showed:
  • increased TSH
  • decreased free T4
  These shifts were mild but worth monitoring.

Overall, soy isoflavones improved metabolic and cardiovascular health without affecting testosterone levels.

Why this matters for men over 60

Men with type 2 diabetes often experience:

• low testosterone
• insulin resistance
• chronic inflammation
• higher cardiovascular risk

This study suggests that soy isoflavones may help improve several of these factors—especially blood sugar control and inflammation—without worsening testosterone levels.

What this means for your daily life

If you’re managing diabetes, low testosterone, or cardiovascular risk, soy isoflavones may offer supportive benefits. They can be consumed through:

• soy protein shakes
• tofu or tempeh
• soy nuts
• isoflavone supplements

However, because the study noted mild thyroid changes, men with thyroid concerns should speak with a healthcare professional before supplementing.

Reference

The study is available here: Effect of Soy in Men With Type 2 Diabetes Mellitus and Subclinical Hypogonadism