What is A1 and A2 casein?
Caseins are one of the kinds of protein found in milk. Two main types are A1 and A2 casein. The only difference between them is one amino acid. A1 has an amino acid called "histidine" in the middle of it and A2 casein has "proline" instead. Otherwise, they are the same.
Does it matter if milk has A1 or A2 casein?
You bet! Having histidine instead of proline on the A1 casein protein makes the protein weaker at that spot. During digestion, it is more likely to break. When it does, it can break into a very short protein called B-casomorphin-7.
What is B-casomorphin-7 and why does it matter?
B-casomorphin is a protein found in milk that has A1 casein after it has been digested. Studies have shown that B-casomorphon-7 shows digestion down which can contribute to the digestive discomfort some people feel after drinking milk.
What do studies on humans show the difference is between drinking milk containing A1 casein compared to just A2 casein?
There are many people who notice a clear positive difference in how they feel after drinking milk with just A2 casein, but what do the studies show? There have been some recent high quality published studies showing differences in digestibility between the two. Milk with A2 casein has been shown to result in less stomach discomfort, less problems with loose stool and less gas and bloating. A couple of studies have even shown improvements for people who have trouble digesting lactose. More studies need to be done since research looking at these differences are just beginning.
Click here to read the largest human study to date.