Does All Milk Have A1 Protein? Unpacking the A1 vs. A2 Debate

November 21, 2025 •

4 min read

Originally, all domesticated cow's milk contained only the A2 beta-casein protein, but a natural genetic mutation over millennia introduced the A1 variant. This has led to widespread consumer interest in whether all milk have A1 protein, and the subsequent rise of A2 milk alternatives claiming digestive benefits.

Quick Summary

Not all milk contains A1 protein; its presence depends on the cow's genetics, with some breeds producing only A2 milk. A1 beta-casein breaks down into a peptide called BCM-7, which some people find harder to digest. A2 milk from specially selected cows does not produce BCM-7, making it a potential option for those with milk-related digestive issues.

Key Points

Not All Milk is A1: The presence of A1 beta-casein is dependent on the cow's genetics, with a natural mutation introducing it to some breeds over time.
A1 and A2 are Different Proteins: A1 and A2 are distinct beta-casein protein variants, with A1's digestion potentially releasing a peptide (BCM-7) that some find problematic.
A2 Milk is A1-Free: Specific brands and milk from certain cow breeds, as well as milk from goats and sheep, contain only the A2 protein.
Potential Digestive Comfort: For some individuals, switching to A2 milk may alleviate digestive discomfort associated with A1 protein, but this is not the same as lactose intolerance.
Limited Health Evidence: While a link to digestive issues is plausible, claims associating A1 milk with other serious chronic diseases are not conclusively proven and require more research.
Check the Label: To avoid A1 protein, consumers should look for milk explicitly labeled as 'A2 milk' or consider milk from non-European animals.

The Genetic Distinction: What are A1 and A2 Beta-Casein?

At the heart of the A1 vs. A2 discussion is a single genetic difference in the beta-casein protein, one of the primary proteins in milk. This difference occurred naturally over centuries, primarily in European dairy breeds such as Holstein-Friesian, and changed one amino acid in the protein chain.

How the A1 Protein Came to Be

The ancestral milk protein in cows, and still found in other mammals like goats and humans, was the A2 beta-casein. However, a natural genetic mutation occurred in some dairy cattle breeds, causing them to produce milk with the A1 beta-casein variant instead of or in addition to the A2 protein. Today, most commercial milk is a mix of both A1 and A2 proteins, sourced from a variety of dairy cows.

The Role of BCM-7

When the A1 beta-casein protein is digested, it releases a peptide called beta-casomorphin-7 (BCM-7). For some individuals, BCM-7 may be linked to digestive issues, such as bloating and discomfort, potentially slowing down the digestion process. Conversely, the A2 protein variant does not release significant amounts of this peptide, which is why it is often marketed as being easier to digest for sensitive individuals.

Which Milks Contain A1 Protein and Which Don't?

It is a common misconception that A1 protein is present in all milk. The truth is, the specific type of beta-casein protein in milk is dependent on the genetics of the animal producing it.

Milk That Contains Both A1 and A2 Protein

Conventional Cow's Milk: The majority of milk available in supermarkets is a blend from dairy herds that contain a mix of cows with A1 and A2 genetics, resulting in a combination of both proteins.
Lactose-Free Cow's Milk: While the lactose is removed or broken down in this product, the A1 beta-casein protein remains, so it is not a solution for those sensitive to the A1 protein.

Milk That is Naturally A1-Free

A2 Milk: Specific brands like a2 Milk® use a process of genetic testing to select and separate cows that naturally produce milk containing only the A2 protein.
Goat Milk: Goats, like humans, naturally produce milk that is predominantly A2 beta-casein.
Sheep Milk: Similar to goats, sheep milk typically contains only the A2 protein type.
Buffalo Milk: Buffalo milk, a staple in many parts of the world, is also naturally free of the A1 protein.

A1 vs. A2: Comparing the Proteins


Feature	A1 Milk	A2 Milk	Remarks
Protein Variant	Contains A1 beta-casein, often mixed with A2	Contains only A2 beta-casein	Varies by cow breed and genetic testing
BCM-7 Release	Releases the bioactive peptide BCM-7 upon digestion	Does not release significant amounts of BCM-7	Key difference influencing digestive experience
Digestive Impact	May cause digestive discomfort for some sensitive individuals	Often reported to be easier to digest for some people	Experience can vary from person to person
Origin	Common in milk from European breeds (e.g., Holstein-Friesian)	Common in milk from older breeds and certain heritage cows (e.g., Jersey, Guernsey)	A genetic mutation caused the shift from A2 to A1
Availability	Widely available in most standard dairy products	Available in specially marked products and certain alternative milk types	Increased availability in recent years due to demand

Research and Health Claims

The health implications of A1 versus A2 protein have been a topic of extensive debate and research. While some preliminary studies have explored potential links between A1 milk consumption and conditions like heart disease or type 1 diabetes, the evidence is largely inconclusive and requires further human clinical trials. The most consistent finding is the reported link to improved digestive comfort for some individuals when switching to A2 milk, although this is not a universal experience and is distinct from lactose intolerance.

Conclusion: Navigating the Milk Aisle

The question of "does all milk have A1 protein?" is definitively answered: no. The presence of A1 protein is tied to the genetics of the dairy animal, and consumers now have a wider variety of options to choose from. For those experiencing digestive discomfort, trying a pure A2 milk product from specific cows or exploring milk from other mammals like goats or sheep could provide relief, though it is important to consult a healthcare professional for persistent symptoms. Understanding the difference between A1 and A2 can empower consumers to make more informed choices based on their personal health and digestive needs.

A Practical Guide to A1 & A2 Milk

Genetics, not all milk: The presence of A1 protein depends entirely on the breed of cow and its genetic makeup, not on milk as a whole.
BCM-7 peptide: Digestion of A1 protein releases BCM-7, a peptide linked to digestive discomfort in some individuals.
A2-only milk: A2 milk is sourced from cows specifically selected to produce only the A2 beta-casein protein.
Non-cow options: Goat, sheep, and buffalo milk naturally contain predominantly A2 beta-casein.
Digestive alternative: For some with milk-related digestive issues, A2 milk offers an easier-to-digest option, distinct from lactose intolerance.

Frequently Asked Questions

The primary difference lies in a single amino acid within the beta-casein protein. A1 milk has histidine at position 67, which can release a peptide called BCM-7 during digestion, while A2 milk has proline at that same position, which does not.

Yes, standard lactose-free cow's milk typically still contains both A1 and A2 beta-casein proteins. It is the lactose (sugar), not the protein, that has been removed or neutralized.

Older, indigenous cow breeds like Jerseys, Guernseys, and Indian Gir cows are known to have a higher proportion of the A2 gene.

No, A2 milk addresses a potential sensitivity to the A1 beta-casein protein, not lactose intolerance. If you have lactose intolerance, you lack the enzyme to digest the milk sugar lactose, which is present in both A1 and A2 milk.

BCM-7 is a peptide released during the digestion of A1 beta-casein. For some individuals, it may slow down digestion and cause gut inflammation, leading to digestive discomfort.

For some people who experience bloating or discomfort after drinking regular milk, switching to A2 milk may improve digestive comfort, though results vary and this is distinct from a confirmed medical intolerance.

No, not all cows within a specific breed are guaranteed to be pure A2. Genetic testing is required to confirm that a cow produces only A2 protein, which is what companies selling 'A2 milk' do.