How do you know if you're A1 or A2?

October 30, 2025 •

3 min read

According to some scientific reviews, A2 milk is easier for some people to digest than conventional milk because of a single protein difference. However, you cannot tell if you're sensitive to the A1 beta-casein protein, or if a specific milk is A1 or A2, just by looking at it.

Quick Summary

The main distinction between A1 and A2 milk lies in their beta-casein protein variants, which can be identified through genetic testing of cows. The key to knowing whether your body tolerates A1 or A2 milk is by observing your own digestive symptoms after a dietary trial, since visual and taste differences are non-existent.

Key Points

Genetic Difference: A1 and A2 milk contain different beta-casein protein variants, determined by the cow's genetics.
Digestive Peptide: During digestion, the A1 beta-casein protein can release BCM-7, a peptide linked to digestive discomfort for some people, while A2 milk does not.
Cannot Be Visually Identified: You cannot distinguish A1 from A2 milk by taste, smell, or color.
Self-Testing: The most practical method to know your personal sensitivity is a dietary elimination and reintroduction test, starting with certified A2 milk.
Mixed Research: Scientific evidence linking A1 milk to broader health issues like diabetes or heart disease is inconclusive and remains a subject of debate.
Cow Breeds: A2 milk comes from specific breeds, often tested to ensure purity, while most conventional milk is a mixture of A1 and A2 proteins.

The debate over A1 versus A2 milk has captivated consumers and researchers alike, fueled by claims about digestive health and broader wellness implications. The fundamental distinction is a single amino acid difference in the beta-casein protein chain: A1 milk has histidine at position 67, while A2 milk has proline. This small change dictates how the protein is digested in the human gut, with A1 milk potentially releasing a peptide called beta-casomorphin-7 (BCM-7) that some believe causes discomfort.

The Genetic Difference: A Tale of Two Proteins

How A1 and A2 Beta-Casein Differ

At its core, the variance between A1 and A2 milk is a matter of genetics. Over time, a natural genetic mutation occurred in some dairy cows, changing the beta-casein protein they produce. The original form, found in ancient cow breeds and most other mammals, is A2. Modern dairy breeds, particularly those from Northern Europe like Holstein and Friesian, are more likely to produce milk with a mixture of both A1 and A2 proteins.

This genetic difference is the root of the entire A1/A2 discussion. The presence of histidine at position 67 in the A1 protein allows digestive enzymes to cleave the protein chain and release BCM-7. In contrast, the proline in the A2 protein forms a stronger bond, preventing this cleavage and significantly reducing or eliminating the release of BCM-7.

How to Test Your Personal Sensitivity

Because you cannot distinguish A1 from A2 milk by taste or appearance alone, determining your personal sensitivity requires a process of elimination. A simple at-home digestive test is the most practical method for most people.

The DIY Digestive Test

Here is a step-by-step approach to testing your milk sensitivity:

Elimination Phase: Remove all conventional dairy milk from your diet for a minimum of two weeks. Be aware that most cheese and other processed dairy products contain A1 protein as well.
A2 Milk Trial: After the washout period, reintroduce only certified A2 milk into your diet. Consume it regularly for two weeks and carefully track your digestive symptoms. Use a journal to note any bloating, gas, stomach pain, or changes in bowel movements.
A1 Milk Reintroduction: After the A2 trial, switch to conventional dairy milk (which contains both A1 and A2 proteins) for another two weeks. Again, meticulously record any symptoms you experience. If you notice a significant increase in digestive discomfort during this period compared to the A2 trial, you may be sensitive to the A1 protein.

Interpreting Your Results

This personal trial can provide strong anecdotal evidence of your body's specific response. However, it's not a scientific diagnosis. If your symptoms are severe, or if you suspect a dairy allergy, it is important to consult a medical professional.

The Scientific Debate: Mixed Evidence

Research on the health effects of A1 and A2 milk is ongoing and has produced mixed results. While some studies suggest a link between A1 milk's BCM-7 and health issues like digestive discomfort and inflammation, the evidence is not conclusive. The European Food Safety Authority (EFSA) and other bodies have stated that there is insufficient evidence to associate A1 milk consumption with chronic non-communicable diseases.

A1 vs. A2 Milk: A Comparison


Feature	A1 Milk	A2 Milk
Protein Type	Contains A1 beta-casein and A2 beta-casein.	Contains only A2 beta-casein protein.
Beta-Casomorphin-7 (BCM-7)	Releases BCM-7 during digestion, which some link to digestive issues.	Does not release significant amounts of BCM-7 during digestion.
Digestive Impact	Some individuals may experience bloating, gas, and stomach discomfort.	Often reported to be easier on the stomach for those sensitive to A1.
Primary Source Breeds	European breeds like Holstein and Friesian.	Indigenous cows and breeds like Guernsey and Jersey.
Flavor and Appearance	Indistinguishable from A2 milk..	Indistinguishable from A1 milk..

Conclusion

Ultimately, whether you are sensitive to A1 or A2 milk is a personal discovery, not a certainty based on appearance or taste. While some scientific studies suggest a link between the A1 beta-casein protein and digestive discomfort in certain individuals, the evidence is not universally accepted for broader health claims. For those who experience mild digestive upset with conventional milk, trying a certified A2 milk product and observing your body's reaction is the most reliable method for determining which type of milk is right for you. Your digestive system is the best indicator, as the difference is internal and molecular, not external. If you have significant health concerns, always consult a healthcare professional before making major dietary changes.

Medical News Today - A2 Milk Benefits and Risks

Frequently Asked Questions

The core difference is a single amino acid in the beta-casein protein chain. A1 milk has a histidine at position 67, which is replaced by proline in A2 milk.

The histidine in A1 protein allows digestive enzymes to cleave the protein chain and release a peptide called BCM-7. This peptide may cause digestive issues like bloating and discomfort in sensitive individuals.

For those sensitive to the A1 beta-casein protein and the BCM-7 peptide it releases, A2 milk is often easier to digest. The proline in A2 milk prevents the release of BCM-7 during digestion.

A2 milk contains the same amount of lactose as A1 milk, so it's not a solution for true lactose intolerance. However, some people who attribute their digestive issues to lactose may actually be reacting to the A1 protein, and find they tolerate A2 milk better.

A2 milk comes from cows that are genetically tested to produce only the A2 beta-casein protein. Breeds like Jersey and Guernsey are more likely to be A2, while many indigenous cattle breeds from Asia and Africa also produce A2 milk.

Some early observational studies linked A1 milk to a higher risk of conditions like type 1 diabetes and heart disease, but the scientific evidence is inconclusive and requires more research. The strongest evidence relates to digestive discomfort.

Certified A2 milk can be found in many grocery stores under specific brand names, such as The a2 Milk Company. Online retailers and local farms that specialize in A2-certified herds are also sources.