Beta casein is one of the proteins in cow’s milk, and is made up of a long strand of 209 amino acids. Chemically speaking, there is only one difference between A1 and A2 beta casein: the amino acid in position 67 in that long chain. A1 milk has an amino acid called histidine in that position. A2 milk has one called proline there instead. A2 is the type of milk typically produced by humans, goats, sheep, and some breeds of dairy cattle.
A very simple difference. The question is: Does that little difference affect human health?
Research indicates that A1 and A2 beta casein are digested differently in the human body. Both forms are broken down into opioid protein fragments called casomorphins. A1, however, is unique in that it releases a form of casomorphin not produced by A2 beta casein. This casomorphin is known as beta-casomorphin-7 (BCM-7).
It appears that it is difficult for the body to break down BCM-7 because the bonds holding this particular casomorphin together are extremely strong. However, BCM-7 is also too large to be absorbed through a healthy adult intestine. It can only be readily absorbed by babies and by people with abnormally permeable intestines. If BCM-7 is absorbed, it enters the bloodstream and binds to the body’s opioid receptors just like any other opioid would. And here is the issue that causes some nutrition experts concern.
Most opioids are known to cause a variety of disorders, ranging from allergy-type reactions in the short term to mental problems and immune difficulties in the long run. What has not been conclusively proven so far is whether or not A1 milk causes the same issues. Natural food proponents point to a variety of anecdotal and epidemiological evidence that appears to link A1 beta casein to many diseases prevalent today:
- Heart disease.
- Milk allergies.
On the other hand, food safety authorities in a variety of countries have declared A1 milk to be perfectly safe, pointing out that the research conducted to date is far from conclusive. Very little research has been funded so far, and what studies are available are considered to be flawed in various ways. The European Food Safety Authority (EFSA) announced in 2009:
Based on this review [of scientific literature available at the time], EFSA concluded that a cause and effect relationship is not established between the dietary intake of BCM7, related peptides or their possible protein precursors and non-communicable diseases.
More progress on the question is not likely to be made without further research.
Most dairy cows will have one of the following gene combinations in their DNA:
- Two genes for A1.
- Two genes for A2.
- One gene for A1 and one for A2.
Cows with A1 genes will produce A1 milk. Cows with A2 genes will produce A2 milk. Cows with a combination of the two genes will produce both types of beta casein in their milk.
It is interesting to note which breeds typically carry which genes. While every breed has some cows that produce A1 milk and some that produce A2 milk, a few breeds are notable for having high percentages of one type of beta casein or the other.
There are a few breeds that mainly produce A2 milk:
Some other breeds are fairly evenly divided between A1 and A2, or have a slight predominance of A1:
In general, the more traditional breeds tend to have the highest percentages of A2 milk. Again, however, there are exceptions. The only way to know for certain if an individual cow or bull carries the gene for A2 milk is to have the animal genetically tested. This is done by pulling hair from the animal and sending it to a laboratory for analysis.