Which protein is better, A1 or A2? A Comprehensive Guide

November 15, 2025 •

3 min read

Over 70% of athletes and a significant portion of the general population experience gastrointestinal issues from consuming cow's milk. This discomfort often hinges on a key difference in milk's protein composition, specifically whether the milk contains A1 or A2 protein. Understanding this distinction can be the key to better dairy tolerance and overall digestive health.

Quick Summary

A1 and A2 are beta-casein protein variants in cow's milk, differing by a single amino acid that affects digestion. A1 protein can release a peptide called BCM-7, linked to digestive discomfort and inflammation in some individuals, while A2 protein does not. Research suggests A2 milk is easier to digest for sensitive individuals, but claims about other health conditions require more study.

Key Points

Single Amino Acid Difference: A1 and A2 beta-casein proteins differ by one amino acid at position 67, critically changing digestion.
BCM-7 Release: A1 protein releases BCM-7 during digestion, linked to digestive issues and inflammation in some individuals.
Easier Digestion with A2: A2 milk is often perceived as easier to digest for dairy sensitivities due to not producing significant BCM-7.
Genetic Origins: A1 is a mutation widespread in modern herds; A2 is the original, found in older/indigenous breeds.
Inconclusive Health Claims: Links between A1 milk and serious conditions like type 1 diabetes and heart disease are controversial and not definitively proven.
Self-Testing is Key: Test A2 milk yourself for a few weeks to see if symptoms improve.

Understanding the Core Difference: One Amino Acid Changes Everything

At the heart of the A1 vs. A2 debate is a single amino acid difference in the beta-casein protein. A1 beta-casein has histidine at position 67, while A2 has proline. This difference affects how the protein breaks down during digestion. When A1 protein is digested, it can release beta-casomorphin-7 (BCM-7), an opioid-like peptide. The proline in A2 protein prevents this release.

The Historical and Genetic Background

The A1 variant is a result of a genetic mutation that occurred in European dairy herds. Modern breeds like Holstein-Friesian often produce a mix of A1 and A2 protein milk. Older or native breeds such as Jersey, Guernsey, Gir, and Sahiwal are more likely to produce milk predominantly containing the A2 protein. Farmers can use genetic testing to produce and market A2-only milk.

A1 vs. A2 Protein: A Comparison of Health Effects

Digestive Health

The release of BCM-7 from A1 milk is thought to contribute to digestive discomfort in some people, including bloating, gas, and stomach pain. Studies have indicated that consuming A2 milk may lead to fewer gastrointestinal symptoms for some individuals. A2 milk is often promoted as being easier to digest for those with sensitivity to conventional milk.

Potential Links to Chronic Diseases

Claims linking A1 protein to conditions beyond digestive issues, such as type 1 diabetes, heart disease, and neurological problems, are controversial. While some studies have suggested correlations, others have not found a definitive link. More large-scale human trials are needed to understand any potential long-term health implications.

Comparison Table: A1 vs. A2 Protein


Feature	A1 Protein (Conventional Milk)	A2 Protein (A2 Milk)
Beta-Casein Type	Contains the A1 beta-casein variant, often mixed with A2.	Contains only the A2 beta-casein variant.
Digestive Byproduct	Breaks down to release Beta-casomorphin-7 (BCM-7), an opioid-like peptide.	Does not release significant levels of BCM-7 during digestion due to a different structure.
Digestibility	Can be more difficult to digest for sensitive individuals due to BCM-7.	Generally considered easier to digest for those with dairy sensitivity.
Associated Symptoms	Linked to digestive issues like bloating, gas, and inflammation in sensitive people.	Associated with fewer digestive symptoms in many individuals.
Cow Breeds	Found in most commercial dairy cows, including Holstein, Friesian, and Ayrshire.	Produced by certain indigenous or older breeds like Jersey, Guernsey, and Gir.
Evidence for Health Links	Some studies suggest correlation with chronic diseases, but evidence is inconclusive and debated.	Generally considered a safer alternative by proponents, with potentially fewer inflammatory effects.
Availability	Widely available and cheaper than A2-specific products.	Increasingly available but typically more expensive due to specialized production.

How to Choose the Right Milk for You

Deciding which protein is better, A1 or A2, is a personal process. If you experience digestive discomfort from conventional milk, trying A2 milk is a reasonable step. Switch to certified A2 milk for a couple of weeks and observe if your symptoms improve. Remember to consider other potential causes of digestive issues, such as lactose intolerance. A2 milk can be a good option for those sensitive to A1 protein, and its increasing availability makes it easier to test for yourself.

Conclusion: Making an Informed Choice

The choice between A1 and A2 protein is significant for those sensitive to conventional dairy. While most people tolerate A1 protein well, A2 milk offers an alternative that doesn't produce BCM-7 during digestion, potentially leading to easier digestion and less discomfort for some individuals. However, be mindful that claims about A1 protein and serious long-term health conditions are not conclusively proven and require more research. If you suspect a sensitivity to A1 protein, trying A2 milk is the best way to determine your personal tolerance and make an informed choice for your health. For further research, consult {Link: Simply Grassfed https://simplygrassfed.com/blog/understanding-the-a2-versus-a1-beta-casein-comparison}.

Frequently Asked Questions

The main difference is a single amino acid at position 67 of the beta-casein protein chain. A1 has a histidine, while A2 has a proline. This distinction affects how the protein is broken down during digestion.

No, there is no discernible difference in taste or appearance between A1 and A2 milk. The difference is purely in the protein structure and its digestive impact.

A2 milk contains the same amount of lactose as conventional milk, so it is not a solution for lactose intolerance. However, some individuals with milk sensitivity, who may have misattributed their symptoms to lactose, find relief when switching to A2 milk due to the absence of the A1 protein.

Indigenous breeds, like the Indian Gir and Sahiwal cows, and heritage breeds like Jersey and Guernsey, are known for producing milk high in the A2 protein. Conversely, Western breeds like Holstein-Friesian commonly produce A1 protein milk.

You cannot determine the protein type by taste or appearance. You must purchase milk explicitly labeled as 'A2 milk', which comes from herds genetically tested to produce only the A2 beta-casein protein.

BCM-7, or beta-casomorphin-7, is an opioid-like peptide released during the digestion of A1 protein. In sensitive individuals, BCM-7 is thought to be associated with digestive discomfort, inflammation, and other adverse health outcomes, though more conclusive evidence is needed for the broader claims.

For those with dairy sensitivity related to A1 protein, A2 milk is considered a healthier choice due to its better digestibility. For the majority who tolerate conventional milk without issues, the health difference is minimal. Definitive links between A1 protein and major diseases are not yet conclusively proven.