What Is A2 Milk? A Guide to Casein Protein Variants
Summary
Not all milk proteins are the same — there are two distinct variants of casein protein found in dairy, known as A1 and A2. The A1 variant is the result of a genetic mutation and can cause digestive issues, while the A2 variant does not carry the same risks. Choosing A2-sourced dairy products, particularly cheese, may significantly improve digestive tolerance.
Key Takeaways
- Casein makes up about 30% of the protein in milk and comes in two forms: A1 and A2
- A1 casein is a genetic mutation, while A2 is the natural, original form of the protein
- The A1 variant allows a compound called BCM-7 to enter the digestive tract, potentially causing bloating and inflammation
- A2 casein does not allow BCM-7 to penetrate the digestive tract, making it easier to digest
- Jersey cows naturally produce A2 milk, making them a preferred source
- Goat and sheep dairy are inherently A2, making their cheeses a safe and recommended option
- If consuming dairy, choosing A2-sourced cheese is preferable to standard cow’s milk cheese
Details
The Two Types of Casein
Casein protein accounts for roughly 30% of the total protein in milk. Within casein, there are two structural variants — A1 and A2 — that differ in the sequence and orientation of their amino acids. This seemingly small difference has significant downstream effects on digestion.
A1 Casein and BCM-7
The A1 variant is classified as a genetic mutation — meaning it arose from a sudden alteration in the genetics of certain cattle breeds over time. When A1 casein is digested, it releases a peptide fragment called BCM-7 (beta-casomorphin-7). This compound is capable of crossing the intestinal barrier and entering the digestive tract, where it can trigger:
- Bloating
- Digestive inflammation
- General gastrointestinal discomfort
A2 Casein and Digestive Tolerance
The A2 variant does not produce BCM-7 in a way that allows it to invade the digestive tract. As a result, A2 dairy is generally far better tolerated by people who experience discomfort from conventional dairy products. Many individuals who believe they are lactose intolerant may actually be reacting to A1 casein rather than lactose itself.
Best Sources of A2 Dairy
| Source | A2 Status |
|---|---|
| Jersey cows | Naturally A2 |
| Goats | Inherently A2 |
| Sheep | Inherently A2 |
| Standard Holstein cows | Predominantly A1 |
When shopping for cheese, look specifically for A2-certified products. One brand mentioned is Cascadia Creamery, which produces cheese exclusively from A2 sources. Cheese made from goat’s milk or sheep’s milk is also a reliable A2 option and widely available.
General Recommendation on Milk
While the focus here is on making better choices if you consume dairy, the overall position presented is that liquid milk is not recommended. If dairy is consumed, cheese from A2 sources is the preferred format.