Soy Protein Isolate
Also: SPI · isolated soy protein · soy isoflavones · genistein · daidzein
Probably fine in moderation — meta-analyses don't show meaningful testosterone or sperm effects at normal intakes; whey or pea protein avoids the question entirely.
Testosterone & hormonal load
Soy protein contains phytoestrogens (genistein and daidzein) that weakly bind estrogen receptors. Multiple clinical meta-analyses find no meaningful change in total or free testosterone, LH, FSH, or sperm parameters at typical dietary intakes. Case reports of gynecomastia and very low testosterone exist but involve supraphysiological intakes (over 12 servings daily). For most men consuming 1–2 servings of soy protein daily, the clinical evidence does not support testosterone suppression.
Found in.
Two jurisdictions, two different verdicts.
Soy protein is a common food ingredient. Soy allergen must be declared under EU Food Information Regulation.
Generally recognized as safe. FDA-allowed health claim: 25g/day soy protein as part of diet low in saturated fat may reduce risk of heart disease.
The receipts.
- [01]Messina 2010 — Soybean isoflavone exposure does not have feminizing effects on men (PubMed)pubmed.ncbi.nlm.nih.gov/20378106/
- [02]Reed et al. 2021 — Soy protein and testosterone in men (PubMed)pubmed.ncbi.nlm.nih.gov/33383165/
- [03]Cederroth et al. 2012 — Soy, phytoestrogens and their impact on reproductive health (PubMed)pubmed.ncbi.nlm.nih.gov/22210487/
Find Soy Protein Isolate before it finds you.
Point the camera at any barcode. Mangood reads the ingredient list and tells you, in one tap, whether Soy Protein Isolate is hiding in the bottle in your hand.