L-Arginine vs Soy Protein Isolate
Amino Acid vs Protein · evidence-backed comparison
- • Soy Protein Isolate has the stronger evidence base (moderate (some rcts)).
- • Soy Protein Isolate has the broader effect profile across the 9 effect categories.
- • L-Arginine is cheaper per serving ($0.35 vs $0.60).
- • Soy Protein Isolate has higher bioavailability (better absorption).
Side-by-side traits
| Trait | L-Arginine | Soy Protein Isolate |
|---|---|---|
Category | Amino Acid | Protein |
Active compound | L-arginine | Soy isoflavones + amino acid blend |
Form available | Powder, Capsule | Powder |
Source | microbial | plant |
Typical dose | 3–6 g daily (acute) | 25–40 g per serving |
Dose range | 3–6 g | 25–40 g |
Loading protocol | — | — |
Best taken with | empty stomach | water or plant milk |
Best time of day | pre-workout | post-workout |
Bioavailability How efficiently the body absorbs and utilizes the compound. | Low (2/5) | High (4/5) |
Onset time | Acute: 60 min | Acute: 45–75 min |
Half-life | ~1 hour | — |
Evidence level Quality and quantity of human research. | Limited (small studies) | Moderate (some RCTs) |
Overall effect Subjective effect magnitude. | Low (2/5) | Moderate (3/5) |
Muscle / strength | Low (2/5) | High (4/5) |
Physical energy | Moderate (3/5) | Low (2/5) |
Focus / cognition | Very Low (1/5) | Very Low (1/5) |
Mood / stress | Very Low (1/5) | Low (2/5) |
Sleep quality | Very Low (1/5) | Low (2/5) |
Immunity | Low (2/5) | Low (2/5) |
Recovery Post-exercise recovery support. | Low (2/5) | High (4/5) |
Longevity / healthspan | Low (2/5) | High (4/5) |
Safety rating 5 = exceptionally well-tolerated; 1 = significant risk profile. | High (4/5) | High (4/5) |
Price per serving Approximate USD per typical daily dose. | $0.35 | $0.60 |
Vegan friendly | Yes | Yes |
Gluten free | Yes | Yes |
3rd-party tested | Yes | Yes |
About L-Arginine
Nitric oxide precursor — but most arginine is broken down in the gut. L-citrulline raises blood arginine more reliably for pumps.
About Soy Protein Isolate
Complete plant protein with all 9 EAAs. Equivalent muscle-building to whey in older adults; mild cardio-protective effects from isoflavones.
Vetted brands, third-party testing, ships worldwide.
Vetted brands, third-party testing, ships worldwide.
L-Arginine safety
Common side effects:
- • GI upset
- • Diarrhea (high doses)
Avoid if:
- • Recent heart attack
- • Herpes flare-ups
Drug interactions:
- • Sildenafil, blood pressure meds
Soy Protein Isolate safety
Common side effects:
- • Mild estrogen-mimicking (debated, minor)
Avoid if:
- • Soy allergy
- • Hormone-sensitive cancers (consult MD)
Drug interactions:
- • Thyroid meds (levothyroxine)
Common uses
- • Pump
- • Erectile function
- • Blood flow
Stacks well with: L-Citrulline
Common uses
- • Vegan muscle gain
- • Heart health
- • Menopause support
Stacks well with: Creatine Monohydrate
Related comparisons
Medical disclaimer
SupplementDuel is for educational purposes only and is not medical advice. Consult a physician before starting, stopping, or combining supplements — especially if you are pregnant, breastfeeding, take prescription medication, or have a chronic condition.