L-Tryptophan vs Soy Protein Isolate
Sleep vs Protein · evidence-backed comparison
- • Soy Protein Isolate has the broader effect profile across the 9 effect categories.
- • L-Tryptophan is cheaper per serving ($0.35 vs $0.60).
- • Soy Protein Isolate has higher bioavailability (better absorption).
Side-by-side traits
| Trait | L-Tryptophan | Soy Protein Isolate |
|---|---|---|
Category | Sleep | Protein |
Active compound | L-tryptophan | Soy isoflavones + amino acid blend |
Form available | Capsule, Powder | Powder |
Source | microbial | plant |
Typical dose | 500–1500 mg | 25–40 g per serving |
Dose range | 500–1500 mg | 25–40 g |
Loading protocol | — | — |
Best taken with | carbs (improves CNS uptake), empty stomach | water or plant milk |
Best time of day | evening | post-workout |
Bioavailability How efficiently the body absorbs and utilizes the compound. | Moderate (3/5) | High (4/5) |
Onset time | Acute: 60 min | Acute: 45–75 min |
Half-life | ~2 hours | — |
Evidence level Quality and quantity of human research. | Moderate (some RCTs) | Moderate (some RCTs) |
Overall effect Subjective effect magnitude. | Moderate (3/5) | Moderate (3/5) |
Muscle / strength | Very Low (1/5) | High (4/5) |
Physical energy | Very Low (1/5) | Low (2/5) |
Focus / cognition | Very Low (1/5) | Very Low (1/5) |
Mood / stress | High (4/5) | Low (2/5) |
Sleep quality | High (4/5) | Low (2/5) |
Immunity | Very Low (1/5) | Low (2/5) |
Recovery Post-exercise recovery support. | Very Low (1/5) | High (4/5) |
Longevity / healthspan | Very Low (1/5) | 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-Tryptophan
Serotonin and melatonin precursor. Generally safer than 5-HTP for daily use, with strong sleep-onset and mood support.
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-Tryptophan safety
Common side effects:
- • Drowsiness
- • GI upset
- • Dry mouth
Avoid if:
- • SSRI use (serotonin syndrome)
- • Liver disease
Drug interactions:
- • SSRIs
- • MAOIs
- • Sedatives
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
- • Sleep onset
- • Mood
- • Carb cravings
Stacks well with: Magnesium Glycinate
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.