What are A1 and A2 milk proteins?

Last updated 31/01/2025

There are different types of proteins found in milk. One of these proteins is called beta-casein, which comes in two forms: A1 and A2. Depending on their genes, cows can produce A1, A2, or a combination of both proteins in their milk. Regular milk typically contains both A1 and A2 proteins.[1] Some farmers selectively breed cows to produce milk exclusively containing A2 protein by ensuring that all cows in the herd have the A2/A2 genotype.

Several studies have looked into the relationship between A1 and A2 milk proteins and health, particularly focusing on digestive discomfort. Some studies have found that people with lactose maldigestion or lactose intolerance experience improvements in digestive symptoms, like stomach discomfort, when they consume milk with only A2 protein.[2] Although more research is needed on larger groups of people, these findings are encouraging for individuals who struggle with discomfort after consuming regular dairy milk.

It's important to note that whether milk contains A1 and A2 proteins or only A2 protein, both are natural components of milk and considered healthy to drink.[3]

---

References

[1] Givens I, Aikman P, Gibson T et al. Proportions of A1, A2, B and C β-casein protein variants in retail milk in the UK. Food Chem. 2012; 139:549-552

[2] Ramakrishnan M et al. Milk Containing A2 β-Casein ONLY, as a Single Meal, Causes Fewer Symptoms of Lactose Intolerance than Milk Containing A1 and A2 β-Caseins in Subjects with Lactose Maldigestion and Intolerance: A Randomized, Double-Blind, Crossover Trial. Nutrients. 2020 Dec 17;12(12):3855.

[3] European Food Safety Authority. 2009. Review of the potential health impact of β-casomorphins and related peptides. EFSA J7, 231.