Why can I drink A2 milk but not milk? The science behind A1 vs A2 protein

December 24, 2025 •

3 min read

While most commercial milk contains both A1 and A2 beta-casein proteins, an estimated 20% of adults experience dairy-related abdominal discomfort, leading them to wonder: 'Why can I drink A2 milk but not milk?' The answer lies in a single amino acid difference and its impact on your digestive system.

Quick Summary

For some, the A1 beta-casein protein in regular milk causes digestive issues, whereas A2 milk, lacking A1 protein, is easier on the stomach, providing dairy benefits without discomfort.

Key Points

Protein Difference: Regular milk often contains both A1 and A2 beta-casein proteins, while A2 milk contains only the A2 variant.
The Peptide BCM-7: The A1 protein can break down in the gut to release the peptide BCM-7, which is linked to inflammation and digestive issues in some people.
Digestive Comfort: The A2 protein is digested differently and does not release the problematic BCM-7, which is why many with dairy sensitivity can drink A2 milk without discomfort.
Not Lactose-Free: A2 milk still contains lactose, the milk sugar. It is only helpful for people sensitive to the A1 protein, not those with true lactose intolerance.
Know Your Sensitivity: Symptoms of A1 protein sensitivity, including bloating and gas, can mimic lactose intolerance, so it is important to distinguish between the two conditions.

The Core Difference: A1 vs. A2 Protein

Regular milk from many Western dairy herds contains a mix of A1 and A2 beta-casein proteins, a result of a genetic mutation that spread thousands of years ago. A2 milk, however, comes from cows selected to produce milk with only the A2 beta-casein protein, similar to the original milk from cows, humans, and other mammals. The key difference lies in the amino acid at position 67 of the protein chain: A2 has proline, while A1 has histidine.

The Peptide Problem: BCM-7

This difference means that during digestion, A1 beta-casein can release beta-casomorphin-7 (BCM-7), an opioid peptide linked to gastrointestinal issues and inflammation in sensitive individuals. The proline in A2 beta-casein creates a stronger bond, preventing or limiting BCM-7 formation and potentially leading to easier digestion for some.

Symptoms of A1 Protein Sensitivity

Symptoms of A1 protein sensitivity often resemble those of lactose intolerance. These can include:

Bloating
Abdominal Pain
Gas
Changes in Bowel Habits
Nausea

A1 vs. A2 vs. Lactose Intolerance: A Comparison

Understanding the distinction between A1 protein sensitivity and lactose intolerance is crucial, as they have different causes but similar symptoms. A2 milk addresses protein sensitivity, not lactose intolerance.


Feature	A1 Protein Sensitivity (often resolved with A2 milk)	Lactose Intolerance (requires lactose-free options)
Cause	Adverse reaction to BCM-7 released from A1 beta-casein.	Insufficient lactase enzyme to break down lactose.
Mechanism	BCM-7 can cause inflammation and discomfort.	Undigested lactose ferments, causing gas and bloating.
Immune System	Not typically a severe immune response.	No immune system involvement.
A2 Milk Effect	Often alleviates symptoms by removing A1 protein.	A2 milk contains lactose and is not helpful.
Other Milk Types	Other mammal milk (goat, sheep, buffalo) is naturally A2-dominant.	Some dairy (hard cheeses, yogurt) has lower lactose.

The Benefits of A2 Milk for Sensitive Individuals

Switching to A2 milk can provide benefits for those sensitive to the A1 protein, allowing them to consume dairy without discomfort while still receiving essential nutrients.

Better Digestive Comfort
Nutritional Equivalency
Versatility in Use
May Support Gut Health

Is A2 Milk Right for You? Making the Switch

If you suspect an A1 protein sensitivity, try an elimination diet: remove all dairy, then reintroduce only A2 milk to see if symptoms improve. It is important to distinguish this from a true milk allergy, which is a serious condition. A2 milk is not a solution for lactose intolerance or cow's milk protein allergy. However, for those sensitive to A1 protein, it can be a valuable alternative.

Conclusion

For many experiencing digestive discomfort from regular milk, the difference lies in the A1 beta-casein protein and its breakdown into BCM-7. A2 milk, containing only the A2 protein, avoids this issue, offering a potentially more digestible option. While nutritionally similar, the A2 milk's protein composition can make a significant difference for sensitive individuals, allowing them to enjoy dairy's benefits without the common side effects. Exploring A2 milk, often from specific breeds, is a worthwhile step for those seeking comfortable dairy consumption.

For more detailed research on the effects of A1 beta-casein, you can review peer-reviewed articles from organizations like the National Institutes of Health.

Frequently Asked Questions

No, A2 milk is not lactose-free. It contains the same amount of milk sugar (lactose) as regular milk. If you are truly lactose intolerant, A2 milk will not resolve your digestive issues.

The best way is through an elimination diet. Try removing all regular milk from your diet for a few weeks, then introduce A2 milk. If your symptoms of discomfort do not return, it is a strong sign of A1 protein sensitivity.

A2 milk comes from cows that have been specifically tested and selected to produce only the A2 beta-casein protein. Many older, traditional breeds of cows, as well as goats, sheep, and buffalo, naturally produce milk with A2 beta-casein.

There are no known unique risks associated with A2 milk compared to regular milk. However, it is still cow's milk and contains lactose and other milk proteins. It should not be consumed by individuals with a cow's milk protein allergy.

A2 milk is not a substitute for infant formula for babies with a cow's milk protein allergy. It is not suitable for infants with galactosemia or true milk allergies. You should consult a pediatrician before introducing any new milk type to a baby's diet.

Yes, milk from other mammals like goats, sheep, and buffalo, as well as human breast milk, naturally contains predominantly A2-like beta-casein proteins and no A1.

Yes, A2 milk can be used in exactly the same way as regular milk for cooking, baking, and other recipes. Its nutritional content is comparable to regular milk.