Whey Protein Isolate (WPI)
Also known as: WPI, Whey isolate, Cross-flow microfiltered whey
Microfiltered or ion-exchange purified whey to ≥90% protein. Lower in lactose and fat than WPC, preserving most bioactive fractions in CFM versions. DIAAS ≈ 1.09; leucine content ~11%.
Last reviewed: 2026-06-28 · 2 indexed studies
Set your location for accurate regulatory status
Saved on this device — no sign-in needed.
Overview
Whey protein isolate is whey filtered to ≥90% protein content with minimal lactose (<1%) and fat (<1%). Cross-flow microfiltration (CFM) or ion-exchange produces a clean, fast-digesting protein with maximal leucine per calorie — ideal for cutting phases, lactose-sensitive users and anyone wanting peak amino acid efficiency.
Mechanism & Function
Mechanism of Action
Fastest aminoacidaemia of any whole-food protein after hydrolysed whey; rapid leucine peak maximally triggers mTORC1-mediated MPS within 60–90 minutes of ingestion.
Physiological Role
Concentrated EAA delivery for MPS with negligible fat/lactose load.
Primary Pathways
Performance / Health Relevance
Witard 2014 showed 20 g of WPI maximally stimulates MPS in young men after resistance exercise; older adults benefit from 40 g. Fast kinetics make WPI the gold standard for post-workout protein when speed matters.
Evidence Review
No meta-analyses or systematic reviews indexed for this ingredient yet.
Dimensions marked N/A have no indexed evidence of that class. They are shown as unavailable rather than scored.
Practical Use & Dosage
- Minimum Effective Dose
- 20 g per serving (young adults); 40 g (older adults)
- Optimal Range
- 20–40 g per serving, 1.6–2.2 g/kg/day total protein
- Upper / Caution Level
- No defined upper limit within total-protein targets
- Timing
- Within 0–2 h post-exercise, or any meal where rapid MPS is desired
- Best Format
- CFM (cross-flow microfiltered) preferred; ion-exchange acceptable but lower bioactive content
- Bioavailability
- DIAAS ≈ 1.09; near-complete ileal digestibility.
- Absorption Considerations
- Very low lactose (<1%) — tolerated by most lactose-intolerant users.
Safety & Interactions
Side Effects
- •Rare GI discomfort
- •Acne in predisposed individuals (anecdotal)
Contraindications
- Milk protein allergy
Drug Interactions
- •May reduce absorption of levodopa, tetracyclines, fluoroquinolones — separate dosing
Who Should Avoid
- •Cow's milk protein allergy
Monitoring
None required in healthy adults.
Frequently Asked Questions
Auto-generated from indexed evidence — dosage, safety, interactions, and more.
When is Whey Protein Isolate (WPI) typically used or indicated?
Whey Protein Isolate (WPI) is most commonly used for: Lactose-restricted diets, Cutting phases, Fast post-workout MPS, Low-fat protein. Concentrated EAA delivery for MPS with negligible fat/lactose load.
How does Whey Protein Isolate (WPI) work?
Fastest aminoacidaemia of any whole-food protein after hydrolysed whey; rapid leucine peak maximally triggers mTORC1-mediated MPS within 60–90 minutes of ingestion.
What is the recommended dose of Whey Protein Isolate (WPI)?
The optimal range is 20–40 g per serving, 1.6–2.2 g/kg/day total protein. with a minimum effective dose of 20 g per serving (young adults); 40 g (older adults). Best taken: Within 0–2 h post-exercise, or any meal where rapid MPS is desired. Upper / caution level: No defined upper limit within total-protein targets.
What are the side effects of Whey Protein Isolate (WPI)?
Reported side effects include: Rare GI discomfort; and Acne in predisposed individuals (anecdotal). Monitoring: None required in healthy adults.
Does Whey Protein Isolate (WPI) interact with medications?
Known or theoretical interactions: May reduce absorption of levodopa, tetracyclines, fluoroquinolones — separate dosing. Always check with a clinician before combining with prescription medication.
Who should avoid Whey Protein Isolate (WPI)?
Whey Protein Isolate (WPI) is generally not recommended for: Cow's milk protein allergy; and Milk protein allergy.
How strong is the evidence for Whey Protein Isolate (WPI)?
Evidence level: Strong (overall score 94/100), based on 2 indexed studies on SuppIndex.
Research & References (2)
Myofibrillar muscle protein synthesis rates subsequent to a meal in response to increasing doses of whey protein at rest and after resistance exercise
Witard OC et al. 20 g whey isolate maximally stimulates MPS in young men post-exercise; 40 g shows only minor additional benefit.
Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men
Tang JE et al. Whey isolate produced greater post-exercise MPS than casein and soy at matched leucine content.
Related Ingredients
Other top-rated ingredients in Proteins & Protein Powders.
Whey Protein Concentrate (WPC 80)
92/100Membrane-filtered (ultrafiltration/microfiltration) liquid whey concentrated to 70–80% protein dry matter. Retains higher levels of native bioactive fractions than isolate. PDCAAS = 1.0; DIAAS ≈ 1.09.
Micellar Casein
88/100Casein retained in its native micellar form (intact αs1, αs2, β and κ caseins assembled with colloidal calcium phosphate). Coagulates at gastric pH, dramatically slowing emptying.
Hydrolysed Whey Protein (WPH)
84/100Enzymatic hydrolysis (typically with pancreatic proteases) breaks intact whey into peptides of 2–10 kDa. Degree of hydrolysis (DH%) is the key quality metric; sports nutrition products typically use DH 10–25%.
Research Overview
Strong EvidenceCite this ingredient
One-click citation export in APA, MLA, Chicago, BibTeX, or HTML. The URL below is stable and safe to link.
Stable URL
https://thesuppindex.com/ingredients/whey-protein-isolate
SuppIndex. (2026). Whey Protein Isolate (WPI): Evidence summary, dosage and clinical studies. Retrieved October 16, 2026, from https://thesuppindex.com/ingredients/whey-protein-isolate
Based on 2 indexed studies · Evidence level: Strong.
Goal Ratings
Stack Compatibility
Pairs with creatine, carbohydrate, leucine, and post-workout stacks.