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Soy Protein (Glycine max isolate)
The best-evidenced plant protein: a complete protein that builds muscle and strength comparably to whey in long-term resistance-training trials, plus the only protein with FDA-recognized LDL-cholesterol lowering.
What the evidence says
Soy Protein doesn't have enough studies with structured effect-size data yet to pool a verdict. Browse the studies below for individual findings.
Most evidence is from high-quality meta-analyses and randomised trials published 1995–2026 with a typical study size of 248 participants.
Based on 226 studies · 26 meta-analyses · 197 RCTs · 582 total participants
Confidence
High confidenceBy outcome
Meta-analyses show soy builds muscle comparably to whey over 6+ weeks and modestly lowers LDL cholesterol (the basis of the FDA claim), with both effects being real but moderate in magnitude.
234 randomised trials
80% were about Soy Protein in an audit of 50 of them
Every randomised or controlled trial of Soy Protein indexed in PubMed, not a hand-picked subset. Meta-analyses and systematic reviews are deliberately excluded from this count: most of them cover many compounds at once, so counting them would inflate it.
PubMed · as of Sep 2026
39 trials ongoing or recruiting · 267 completed on ClinicalTrials.gov
31 of the completed trials have posted results
Registered trials show research momentum for Soy Protein, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Oct 2026
Under EU law (Reg. 1924/2006), EFSA reviews whether a specific health claim for Soy Protein meets the evidence standard. These are independent regulatory decisions on claims — not studies, and never counted toward the evidence score above.
Not authorised by EFSA
“Soy protein Support antioxidant status Radicals associated with exercise”
“Not authorised” means the specific claim wording did not meet the EU’s evidence standard — often a matter of dossier or phrasing, not proof of no effect. EFSA judges marketing claims and is kept separate from our study-based evidence score.
Source: EU Register of nutrition and health claims (European Commission / EFSA) · register snapshot Feb 2013
Soy protein (from Glycine max) is a plant protein.
It is a complete protein — it supplies all nine essential amino acids with a high PDCAAS (~1.0) — and despite a slightly lower leucine content than whey, meta-analysis of long-term (≥6-week) resistance-training trials finds soy produces gains in strength and lean body mass that are statistically indistinguishable from whey or other animal proteins.
Acute muscle-protein-synthesis studies do favor whey (higher leucine, faster digestion), but that edge washes out over weeks when total protein is adequate.
Soy is also unique among proteins for its cardiometabolic effect: a large body of randomized trials and the landmark Anderson NEJM meta-analysis show soy protein modestly lowers total and LDL cholesterol (on the order of ~3-13% depending on baseline and dose), which underpins the FDA's authorized heart-health health claim for soy protein.
It naturally contains isoflavones (phytoestrogens); current evidence does not show meaningful adverse hormonal effects at dietary intakes in men or women.
Supplies all essential amino acids (high PDCAAS ~1.0), driving muscle protein synthesis even though leucine is slightly below whey.
Replacing animal protein with soy protein lowers total and LDL cholesterol — the basis of the FDA soy heart-health claim.
How Soy Protein works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
Discuss total protein intake with your clinician.
Separate soy intake from levothyroxine by several hours.
Generally fine as a food protein in normal amounts.
Soy protein reduces absorption of thyroid hormone replacement; separate dosing and monitor levels if hypothyroid.
Tip: Reduce serving; split doses
Tip: Avoid if soy-allergic
Soy Protein has an evidence score of 6.5/10 — moderate evidence based on 226 indexed studies, including 5 meta-analyses. The best-evidenced plant protein: a complete protein that builds muscle and strength comparably to whey in long-term resistance-training trials, plus the only protein with FDA-recognized LDL-cholesterol lowering. Representative study: PMID 7596371.
The commonly studied dose of Soy Protein is 20-40g per serving for muscle (aim ~2-3g leucine); ~25g/day is the level associated with cholesterol lowering (the cited meta-analysis averaged 47g/day). Individual needs vary — start at the lower end of the range and adjust based on how you respond.
Timing is flexible for Soy Protein — consistent daily use matters more than the time of day. Total daily protein matters most for muscle; for cholesterol, the cited meta-analysis studied soy protein replacing animal protein at an average of 47g/day.
Soy Protein is generally well-tolerated and considered safe for most healthy adults at recommended doses. Reported side effects include allergic reaction, bloating/GI upset. How often they occur is not established for all of them. Use caution if any of these apply to you: Soy allergy.
Creatine
Likely helpsIncreases phosphocreatine stores for faster ATP regeneration, boosting strength, power output, and cognitive function under stress.
Whey Protein
Likely helpsComplete protein with high leucine content that maximizes muscle protein synthesis.
Arginine
Likely helpsPrimary substrate for nitric oxide production — dilates blood vessels to improve circulation, exercise performance, and cardiovascular health.
Beta-Alanine
Likely helpsIncreases muscle carnosine to buffer acid during high-intensity exercise, extending endurance for 1-4 minute efforts.
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Reviewed by Dr. Baher Al Hakim · Last reviewed June 2026 · evidence from 226 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
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