Protein is an essential nutrient which contributes to many different physiological functions. Milk contains proteins in different forms, predominantly casein and whey. Cow’s milk is casein dominant, and A2 protein milk refers to a particular type of casein called ‘beta-casein’. In cow’s milk there are 12 types of beta-casein¹. Of these 12 types of beta-casein, the most common are A1 and A2 beta-casein¹. It is the genetics of the cows that determine which beta-caseins they produce in their milk. Cows can produce A1, A2 beta-casein or more commonly a mixture of both. Milk from the Guernsey breed of cows is mainly A2 beta-casein, but most European cattle produce a mixture of A1 and A2 beta-casein². A2 protein milk is simply milk that comes from A2 protein milk-producing cows.

What is the difference between A1 and A2 beta-casein?

The A1 and A2 beta-casein proteins are long chains of amino acids that are identical apart from the position of one amino acid: A1 has histadine at position 67 of the amino acid chain, and A2 beta-casein has proline at position 67 of the amino acid chain³.

The difference this makes is very subtle.  These large protein chains are broken down into shorter peptides which then differ in each milk due to the histadine and proline⁴. These shorter peptides are digested slightly differently from each other.

Human milk beta-casein

Feeding babies with breastmilk is the best nutrition that they can get and is recommended as a sole source of nutrition for the first six months of life, and then continued on until a child’s second birthday. The protein content and structure of human milk differs from cow’s milk. Human milk does contain beta-casein, and like A2 protein milk also has a proline at the same position of the beta-casein protein chain⁵.

The evidence base for A2 protein milk

At the moment, the research in this area is in its infancy. There are some clinical trials so far that have shown some adults who experience digestive symptoms when they drink milk containing A1 protein, find they can tolerate A2 protein milk^6-8. More research is needed to confirm any benefits of drinking A2 protein milk.

Why would parents use a formula based on A2 protein milk?

The protein composition of formula milk has been a mixture of A1 and A2 beta-casein for many decades and has been safely used. Formula milks based on A2 protein milk are shown to be safe and support normal growth in healthy term infants⁹. The composition and manufacturing process for A2 protein milk are similar to standard formula milks. The difference is in the digestion of the protein chains. Some families already choose to buy milk from farmers who have cows that produce A2 protein milk, and formula based on A2 protein milk is simply for those who would prefer to offer that to their babies as well.