Cows graze in pastureRadiance Dairy, a Fairfield, Iowa, top-rated farm in Cornucopia's Organic Dairy Scorecard, is breeding exclusively for A2 milk.

By Kestrel Burcham, JD

There is some buzz in the dairy marketplace about A2 milk — but what is it? And why do some people claim it solves the gastrointestinal issues that drinking cows’ milk usually gives them?

A Difference in Milk Proteins

The two major types of protein in cows’ milk are casein and whey. Whey makes up about 18% of the total protein in cows’ milk, and casein accounts for the remaining 82%. Casein is where we see the difference between A2 milk and the A1 milk commonly found in the dairy cooler.

About one third of the casein in cows’ milk is beta-casein. The genetic profile of the individual cow dictates which variant of beta-casein is in the milk – there are 13 genetic variants of beta-casein in dairy cattle, including A1, A2, and B (also found in human milk).

All cows’ milk contained the A2 variant of beta-casein until a genetic mutation occurred in European cattle, thousands of years ago. Cattle in Africa, India, and other areas of Asia still produce predominantly A2 beta-casein. However, dairy with A1 beta-casein makes up the majority of milk in the US and Europe, mostly due to trends in breeding over time.

Ultimately, the only way to know whether a given cow produces A2 or A1 milk is through genetic testing.

Research Showing Possible Health Benefits of A2 Milk

Further investigation is needed to definitively determine whether there are widespread health benefits to drinking A2 milk rather than A1. However, studies have shown that individuals digest the A1 and A2 variants of the bovine casein protein differently.

Recent evidence also indicates a correlation between gastrointestinal issues and the consumption of A1 milk in some individuals.

Self-Diagnosing an Inability to Digest Lactose

Many people self-diagnose lactose intolerance (the inability to fully digest the milk sugar lactose) based on gastrointestinal symptoms they experience after consuming dairy, especially milk. Those symptoms often include diarrhea, gas, bloating, and other discomfort.

In a 2015 study, individuals self-diagnosed as lactase non-persistent (commonly referred to as “lactose intolerant”) experienced improvement of symptoms when they drank A2 milk instead of the more common mix of A1 and A2 milk. Many people laud A2 milk as the solution to their problems digesting lactose, but lactose remains the same in A1 and A2 milk. It is more likely that these individuals are reacting to the A1 variant of beta-casein.

The inability to digest lactose is also a different issue than a dairy allergy. A dairy allergy occurs when the body has an immune response to one or more proteins in milk. The most frequent symptoms of a cows’ milk protein allergy are gastrointestinal, but reactions vary. In fact, milk is one of the most common food allergens.

Milk’s Complexity and Health Effects

The protein in cows’ milk is a common source of bioactive peptides (BP) in North American diets. (These peptides are released by the digestion of both caseins and whey proteins.) BP may adversely affect the health of some individuals by increasing the risk of insulin-dependent diabetes when they consume dairy containing A1 or B beta-casein variant.

Current research suggests that A1 beta-casein may function as an immunosuppressant and impair tolerance to dietary antigens in the gut immune system, which may contribute to the onset of type 1 diabetes.

More research is needed to determine the pathways of disease, but it is clear that different caseins produce different peptides during digestion. Specifically, A1 beta-casein may produce the peptide BCM-7 during typical digestive processes, but it is not a product of A2 beta-casein digestion.

Ultimately, bioactive peptides play a significant role in human health through their effects on the digestive, endocrine, cardiovascular, immune, and nervous systems. It is thought that the type of BP produced by milk consumption is impacted by the type of beta-casein being digested.

Studies are ongoing and more research is needed to verify the range and nature of the effect different milk proteins have on individual bodies.


Every individual has distinct health needs. Some people will tolerate A1 milk just fine, while others may find their bodies prefer A2 milk. Still others, whether sensitive or allergic to dairy, will not be able to tolerate milk at all. In addition, only a minority of the global population is lactase persistent and can digest milk sugars after weaning. These health considerations, along with ethical, environmental, and personal preferences, will inform individual choices.

If you’re interested in finding A2 milk, you may have to look beyond your supermarket shelves. The A2 Milk Company was the first to commercialize A2 milk. However, this brand does not produce an organic line. Like all conventional dairy, it is likely to contain agrichemical and drug residues and trigger animal welfare and environmental concerns.

While some cattle breeds are more likely to produce the A2 variant, genetic testing is the only way to ensure the product is free of A1 milk. Goat, sheep, and buffalo milk may also contain A1 beta-casein. A2 herds are being developed in the US and other countries as interest in the different beta-casein proteins increases. Check with your local farmstead dairies to see if they provide this option and consult our list at the bottom of this article.

As detailed in Cornucopia’s report, The Industrialization of Organic Dairy: Giant Livestock Factories and Family Farms Sharing the Same Organic Label, organic milk produced by community-scale farmers also has a myriad of benefits. Consumers seeking milk that is both organic and A2 can find that information on Cornucopia’s organic dairy scorecard in the “products” description for each brand.

Sidebar: Digesting Lactose and Lactase Non-Persistence

Humans are the only mammal that drinks milk — particularly the milk of other animals — past weaning. In most humans, the ability to digest lactose, the main carbohydrate present in milk, declines rapidly after weaning because of decreasing levels of the enzyme lactase.

Ancient cattle herding populations in Africa and Europe developed a genetic mutation that gave them the ability to produce the lactase enzyme into adulthood. Currently, about 65% of the US population is “lactase persistent” (able to digest lactose), but only 25% of the global population is able to digest lactose.

Most people with lactase non-persistence still produce some lactase enzyme and can include varying amounts of dairy in their diets without symptoms. (Lactase non-persistence may be referred to as “lactose intolerance,” although that term is becoming outmoded in the scientific and medical communities.) Often, these individuals have an easier time digesting cheese and yogurt because the fermentation process breaks down some of the lactose sugar in milk.

Lactose non-persistent individuals can typically consume lactose-free dairy products without experiencing side effects.

Lactose non-persistence has also helped drive the market for plant-based beverages. There are many organic, non-dairy options that can mimic the experience of dairy milk, although the two are not nutritionally equivalent foods. Plant-based beverages often contain stabilizers, sweeteners, and synthetic vitamins. Read Cornucopia’s report, “Pouring” Over Plant-Based Beverages, to learn more. Use Cornucopia’s Plant-Based Beverages Scorecard to choose the healthiest option in your store.


Gonca Pasin, Ph.D. February 9, 2017. “A2 Milk Facts.” California Dairy Research Foundation.

Clemens RA. February 16, 2011. “Milk A1 and A2 peptides and diabetes.” Nestle Nutr Workshop Ser Pediatr Program. 2011;67:187-95. doi: 10.1159/000325584.

Ken Rabas. 2015. “A2 Milk: Golden Opportunity for Dairy.” The Milkweed, February.

University of California, Davis, Veterinary Medicine website. 2018. “Beta Casein – A2 Genotyping.” Accessed November 13, 2018.

Bell S, Grochoski G, & Clarke A. 2006. “Health Implications of Milk Containing Beta-Casein with the A2 Genetic Variant.” Crit Rev Food Sci Nutr. 46(1):93-100.

Ho S, Woodford K, Kukuljan S, and Pal S. September 2014. “Comparative effects of A1 versus A2 beta-casein on gastrointestinal measures: a blinded randomised cross-over pilot study.” Eur J Clin Nutr. 68(9):994-1000. Doi: 10.1038/ejcn.2014.127.

Simon Brooke-Taylor, Karen Dwyer, Keith Woodford, Natalya Kost. September, 2017. “Systematic Review of the Gastrointestinal Effects of A1 Compared with A2 β-Casein.” Advances in Nutrition, 8(5): Pages 739–748,

Mayo Clinic website. 2018. “Lactose Intolerance.” Accessed October 23, 2018.

Jianqin S, Leiming X, Lu X, Yelland G, Ni J, and Clarke A. 2015. “Effects of milk containing only A2 beta casein versus milk containing both A1 and A2 beta casein proteins on gastrointestinal physiology, symptoms of discomfort, and cognitive behavior of people with self-reported intolerance to traditional cows’ milk.” Nutr J. 15:35. Doi: 10.1186/s12937-016-0147-z.

Tishkoff S. et al. January 2007. “Convergent adaptation of human lactase persistence in Africa and Europe.” Nat Genet. 2007 Jan; 39(1): 31–40.

Andrew Curry. 2013. “Archaeology: The milk revolution.” Nature News at Nature Publishing Group, July 31.

Mayo Clinic website. 2018. “Milk Allergy.” Accessed November 13, 2018.

Giovanna V, et al. July 23, 2012.“The immunopathogenesis of cow’s milk protein allergy (CMPA).” Ital J Pediatr. 38: 35.

American College of Allergy, Asthma, & Immunology website. 2014. “Milk & Dairy Allergy.” Accessed November 13, 2018.

Kaminski S, Cieslinska A, Kostyra E. 2007. “Polymorphism of bovine beta-casein and its potential effect on human health.” J Appl Genet. 2007;48(3):189-98. DOI: 10.1007/BF03195213.

Sánchez A, Vázquez A. April 12, 2017 “Bioactive peptides: A review.” Food Quality and Safety, Volume 1(1):29–46.

Trivedi, M., & Clarke, A. 2015. “Implications of Bovine beta casein subtypes in health and homeostasis.” Proceedings of the Nutrition Society, 74(OCE5), E301. doi:10.1017/S0029665115003481.

The A2 Milk Company. 2017. “Homepage.” Accessed November 17, 2017.

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