Randomised controlled trialindependent cross-checkabstract checked I-DRY-114 in-depth review
A2 milk no better than ordinary milk in a US trial
Comparative effects of conventional cow's milk versus milk free of A1-type beta-casein on gastrointestinal physiology and symptoms of digestive discomfort in participants intolerant to conventional cow's milk: a pilot randomised controlled trial.
Overview
Greenway FL et al.. Nutr J 2026 · PMID 41634798 · DOI 10.1186/s12937-026-01288-9
No differences in symptoms, gut transit or immune markers.
Does the study support the specific claim? No · Methodological quality: moderate
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Test A2 milk in people who feel unwell after milk.
- How was the study done?
Double-blind crossover RCT.
- How many people, animals or samples were studied?
50 adults.
- What was actually found?
No differences.
- How large was the observed effect?
No significant effects.
- What do the results mean in everyday life?
A1 protein may not be the cause of milk discomfort.
- What are the study's limitations?
Small pilot; company-sponsored.
- What does it say about Elawady's specific claim?
Contradicts the claim.
- Do the results apply to Germany and Europe?
Applicable.
- What can explicitly not be concluded from this study?
Cannot exclude small effects.
Scientific in-depth review
1. Full reference
- Authors
- Greenway FL et al.
- Journal
- Nutr J
- Year
- 2026
- Identifier
- PMID 41634798 DOI 10.1186/s12937-026-01288-9
- Verification
- verified – PubMed efetch 2026-10-26
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
Sponsored by The a2 Milk Company (full text); first author received travel funding from the company.
2. Research question
Does A1-free milk reduce GI symptoms and change transit or immune markers compared with conventional milk?
3. Study design and population
- Study design
- Randomised controlled trial – Single-site, double-blind, randomised crossover pilot trial; SmartPill transit measurement (NCT06763185)
- Population
Non-regular milk drinkers aged 18-68 with self-reported cow's milk intolerance (USA)
- Country
USA (Pennington Biomedical Research Center)
- Period
not stated
- Sample size
50 completers (25 per sequence)
- Inclusion and exclusion criteria
Self-reported mild-to-moderate digestive discomfort after milk
4. Methods and endpoints
- Exposure / intervention
A1-free (A2) milk three times daily
- Comparator
Conventional A1+A2 milk
- Endpoints
GI symptoms, stool, transit times, IgG, IgE, IL-4, SCFA, thiols
- Statistical methods
Crossover comparisons; exploratory (no power calculation)
5. Actual results
- Results
No statistically significant between-group differences in stool frequency/consistency, overall or individual GI symptoms, GI transit times, or IgG, IgE, IgG1, IL-4, SCFA or thiol levels. Post-hoc correlations with urinary galactose in the A1-free arm only.
- Absolute risks
not reported
- Authors' conclusion
The study failed to demonstrate the expected differences in primary outcomes; individuals with preserved lactase activity may benefit more from A1-free milk (exploratory).
6. Strengths
- Double-blind crossover
- Objective transit measurement
- Null result published despite sponsor
7. Weaknesses
- Pilot, no power calculation
- Self-reported intolerance
- Post-hoc correlations
8. Risk of bias
- Orienting tool
- RoB 2
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- some concerns
- Rationale
Industry sponsor; null primary outcomes.
9. Assessment of the statistical interpretation
Null primary outcomes; correlations exploratory.
10. Relevance to the specific claim
Directly tests the claimed A1 effects on symptoms, transit and immune markers and does not confirm them.
11. Independent contrary findings
A-DRY-10 (positive Chinese trial).
12. Transferability to Germany and Europe
US adults.
13. Overall methodological judgement
Weakens the A1 claim.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | moderate |
| Risk of bias | some concerns |
| Precision of results | low |
| Directness | direct |
| Reproducibility | not replicated |
| Consistency with the overall evidence | inconsistent |
| Regional transferability | moderate |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
Larger independent trials.
15. Linked fact checks
- A1 beta-casein in conventional milk releases beta-casomorphin-7, which triggers gut inflammation, slower transit and worse symptoms (shown in a 2016 randomised trial). – Studies contradicting or limiting the claim