Milk Distress?

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Lactose, the type of carbohydrate found in milk, is not well digested in approximately 15% of people of northern European descent, up to 80% of blacks and Latinos, and up to 100% of American Indians and Asians; causing gas, bloating, and diarrhea. Yet perhaps there’s more to not tolerating milk than lactose.

In recent years, research into the specific types of protein found in cow’s milk, and how those proteins affect health, has provided intriguing new information.

Milk protein 101

The protein in cow’s milk comes from two sources, casein and whey.  Casein, the “solid” part of milk, comprises about 80% of milk protein. Whey proteins, found in the liquid part of milk, make up the other 20%. Casein is composed of four different categories, with A1 and A2 beta-casein the most common. Recent research shows that the A1 protein may cause gastrointestinal distress in some people, and possibly may be implicated in developing some chronic health conditions.

Thousands of years ago, cow’s milk contained only the A2 beta-casein protein. A genetic mutation 5,000-10,000 years ago in some northern European cows led to the development of the A1 protein. Depending on the individual cow’s genetic make-up, the cow may produce milk that contains only the A1 protein, only the A2 protein, or a combination of both. In the United States, most cows produce milk that contains both A1 and A2 proteins.

A1 protein and digestive distress

Digestion of A1 beta-casein yields the peptide BCM-7, which seems to trigger inflammation in the digestive tract, leading to gas, bloating, and diarrhea also found in lactose intolerance. For some people, it’s not the lactose that causes trouble, it’s the A1 protein.

A possible role for A1 beta-casein in health

A2 beta-casein is not only easier to digest than A1 beta-casein, it also appears that the peptide BCM-7 produced from A1 casein may negatively affect endocrine, nervous, and immune system receptors. This disruption may possibly lead to increased risk of heart disease, type 1 diabetes, and autism in some people. More research is needed to discover the exact role that A1 beta-casein plays in these conditions.

What about sheep or goat milk?

Both sheep and goat milk contain lactose, but only the A2 beta-casein protein.  This may be why some people are able to tolerate these types of milk and not cow’s milk that contains both the A1 and A2 beta-caseins.

Does human breastmilk also contain the A1 beta-protein?

Human breastmilk only contains the A2 beta-protein that appears to be far better tolerated

How do dairies produce A2 milk?

Milk that only contains the A2 beta-casein protein comes from cows that genetically do not produce the A1 protein. Dairy farmers can breed cows that do not produce A1 beta-casein, and the milk from these cows will only contain the A2 protein.

Is A2 milk safe for people with a cow’s milk allergy?

People diagnosed with cow’s milk allergy need to avoid all types of cow’s milk, including lactose-free milk and A2 milk. An allergy to milk can cause hives, upset stomach, vomiting, bloody stools and anaphylactic shock, which is a life-threatening allergic response.

If I’m lactose intolerant, is A2 milk better for me?

A2 milk contains the same amount of lactose as regular cow’s milk; only the type of beta-casein protein is different, not the lactose. If you’re lactose intolerant, use lactose-free milk or over-the-counter pills or drops that contain the lactase enzyme.

Our recommendations:

All cow’s milk contains the same amount of protein, vitamins and minerals and is a nutrient-dense food that can be a part of an overall healthy eating pattern. The only difference in A2 milk is that it may be more easily tolerated by some people.

If you experience gas, bloating, or diarrhea when you drink milk or eat milk products like yogurt, ice cream, and cheese; talk with your physician about a possible lactose intolerance.

If drinking lactose-free milk still causes digestive problems, try A2 milk.

A2 milk is not recommended for people diagnosed with cow’s milk allergy or lactose intolerance.

There are a couple of dairies in the US that produce A2 milk. is one place you can go and do a search to see who carries it in your area.

—- By:  Lynn Grieger, RDN, CDE, CPT, CHWC


Swagerty D, Walling A, Klein, R. Lactose Intolerance. Am Fam Physician. 2002 May 1;65(9):1845-1851.

Science News. Further Knowledge Required About the Differences Between Milk Proteins.  published 4-28-17, accessed6-20-17.

Pal S, Woodford K, Kukuljan S, Ho S. Milk Intolerance, Beta-Casein and Lactose. Nutrients. 2015;7(9):7285-7297. doi:10.3390/nu7095339.

Jianqin S, Leiming X, Lu X, Yelland GW, Ni J, Clarke AJ. 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. Nutrition Journal. 2015;15:35. doi:10.1186/s12937-016-0147-z.

Chia JSJ, McRae JL, Kukuljan S, Woodford K, Elliott RB, Swinburn B, Dwye KM. Nutrition & Diabetes (2017) 7, e274; doi:10.1038/nutd.2017.16. Published online 15 May 2017

American College of Allergy, Asthma, and Immunology. Milk and Dairy Allergy.  Accessed 6-2-17

—- By:  Lynn Grieger, RDN, CDE, CPT, CHWC

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