Got Cow’s Milk Intolerance? Let’s Learn More.

We know lactose, the sugar in milk, can cause gastrointestinal (GI) symptoms in those with lactose intolerance. A decline in the production of the digestive enzyme, lactase, that cleaves the 2 chain sugar, lactose, into its digestible sugar components of glucose and galactose, can lead to troubling GI symptoms such as gas, bloating, and  diarrhea. Lactose intolerance is the most common food intolerance, globally.

But… can intolerance to dairy products exist beyond the sugar content (lactose) in cow’s milk? To be clear, I am not talking about a milk allergy (an immune mediated, potentially life threatening reaction) but rather an intolerance to other components in milk.

In my practice, working with many patients with digestive symptoms, I find that small subset of my clients exhibit food intolerance symptoms with the ingestion of any cow’s milk and cow’s milk products, even if they are lactose free. Most often these clients suffer with constipation or IBS-C and note symptom exacerbation with the consumption of any type of products made with cow’s milk.


So, I have started to delve a bit into the research. Years ago, I read that the protein, casein in cow’s milk may play a role in dairy intolerance. An 8 ounce glass of milk contains about 6-8 grams of casein, of which, 2-3 grams is beta-casein. Beta-casein can be present in two forms: A1 and A2. As cow’s became domesticated globally, the type of beta-casein they produced changed via a genetic mutation. Back in the day, cows only produced A2 beta-casein, but this has changed over time. In the US, most cow’s milk contains an even mix of A1 and A2 beta-casein. The protein component (amino acids) are arranged differently in A1 vs. A2 milk. Interestingly, human, sheep and goat milk have similar beta-casein protein chains to that of the A2 NOT A1. I wonder if this explains why some of my clients can tolerate goat’s milk better than dairy milk? (FYI: goat and sheep milk still have lactose!)

What’s the difference between A1 and A2 casein? A1 casein, when digested, produces a fragment called beta-casomorphin-7 (BCM-7). BCM-7 is associated with inflammation in the intestine and slowing down gastrointestinal transit time. It actually acts like an opioid, slugging gut movements.  A2 casein, on the other hand, releases very little BCM-7.

For more scientific reading on this topic, click here. In animal studies, A1 beta casein was shown to increase the inflammatory marker myeloperoxidase (MPO) compared to milk containing A2 beta casein; Link here

So, I reached out to Bonnie Johnson, MS, RDN, Vice President Scientific Affairs & Activation The a2 Milk Company to learn more about the beta-casein in milk. The a2 Milk Company produces a milk product called a2 milk, that contains only the A2 beta casein. Here are a few of the questions I posed along with Bonnie’s answers:

Kate: Do you think everyone should be consider switching to A2 milk or is the benefit more for those with dairy intolerance or GI symptoms?

Bonnie: People who are already drinking milk, with no digestive symptoms, can keep drinking the same milk—there’s no reason to switch. However, because a2 Milk is ‘just milk’ it can be enjoyed by everyone in the household. There’s no reason to keep multiple “milks” on hand!

Kate: Can you discuss the potential effects of A1 milk —particularly on small bowel inflammation? Any impact on colonic inflammation?

Bonnie: When A1 protein is digested it releases a 7 amino acid fragment called BCM-7 that starts the inflammatory process high in the small intestine. Unrelated research suggests that when inflammation starts high up in the gut, the cascade of inflammatory particles may impact gastrointestinal tissue through the lower gastrointestinal tract too.

Kate: Any changes in the gut microbiome related to A1 vs. A2 milk?

Bonnie: Nothing specific as of now. However, it is a priority issue for The a2 Milk research platform.

Kate: When do you think A2 milk will be widely available nationwide? 

Bonnie: It’s hard for me to speculate. As sales continue to grow in CA and demand for product grows across the country, we will move into more and more markets. 

Kate: Is there any human studies looking at A1 milk in IBS or IBD specifically?

Bonnie: There is currently a study being conducted in Australia at Monash University that is looking specifically at the effects of A2 beta-casein protein on IBD.

No surprise… those smart scientists at Monash University, who developed the low FODMAP approach are right on top of this science and currently studying A2 beta-casein on inflammatory bowel disease!

A2 milk is available widely in California and spotty in other areas in the US. To see if A2 milk is near your home, click here.

Just last week, David Katz, MD wrote an article on A2 milk in Forbes. Check out this informative article here.

There is always something to learn, right?

13 replies on “Got Cow’s Milk Intolerance? Let’s Learn More.

  • Cate

    Hi, Kate. Thank you so much for the work you do and for writing this blog. I’ve been on a low FODMAP diet now for 2 years (with a lot of help from your blog!) and the results have totally changed my life. Here’s my question: I’ve had several friends who, like me, are on gluten-free diets tell me that when they’ve traveled in Europe, they were able to eat all wheat products — breads, pasta, etc. — without experiencing any GI problems. Why would this be true?

    • katescarlata

      Hey Cate, I hear this all the time. It’s possible that our hybridized wheat is different in the US—may contain more amylase trypsin inhibitors than other wheat varieties–which have been shown to have some immune effects in the gut. In the states–we include many additives to our bread too–that may play a role. We add wheat gluten to many of our commercial breads along with high fructose corn syrup. I also wonder if lowered stress plays a role in some–as some individuals with IBS are known to have more mast cells in the gut–mast cells release inflammatory chemicals and can be induced with stress. Probably not one thing–but perhaps a couple reasons that wheat is often tolerated better in Europe.

      • Holly

        Wow. This is terrific info. That explains what I’ve run into myself and now I understand what “A2 milk” is! I live in California and thought it was just some kind of gimmick. I’ll give it a try now.

        And two for one on the blog today with Cate’s question. I’ve noticed the same thing with pasta. Now we buy only pasta from Italy at Trader Joe’s. The Italian pasta ingredient list shows “durum wheat semolina” with no comma. On the front it also says “Made from 100% hard durum semolina” which means it’s the whole grain in the same proportions as the original grain (germ, bran and endosperm) Whereas most of the pasta from the states says “semolina, durum flour” which are two separate ingredients. The semolina is made from durum wheat but only includes part of the grain.

        Good explaination of it on

        On the Italian pasta label, I believe it would be equally correct to say “whole durum wheat” but since when comparing with brands that say “semolina, durum flour” it would seem that something is missing.

        Thanks again. I love this blog and the work you do, Kate.

    • dkaj

      Kate Thanks for all your hard work. No doctor has ever explained the detailed information or supporting clinical trial information you just provided. I have read info on the differences between the 2 different proteins from various sites, but it’s good to see some actual clinical trial data supporting this. We will be definitely giving this another go trying the A2 or goats milk. It would be wonderful if they came up with a cheese or ice cream made with the A-2 milk. My dd doesn’t drink milk, but does have some of the short aged cheeses. Also, it will be interesting to see if some of your blog followers people report back stating whether or not they have noticed improvement on the A2 milk especially when it comes to constipation issues. This is for the other Cate, in regards to your question on European breads, one might have to question whether or not your friends are eating sourdough breads vs conventionally baked breads with packaged yeasts while traveling? True 24 hour sourdough bread reduces the amount of gluten and fermentable carbs. This could be part of the equation. Or, I would be be curious to know what type of wheat is being used for their bread baking? If it’s a variety of one of the more ancient grains. I agree with Kate, lots of additional preservatives added to all of our foods in the US including our bread which makes it very hard to nail down. One thing I have noticed is my dd does much better with any bread I bake myself without malted barley in the flour. Malted barley flour is the second ingredient in almost all white wheat flours in the US. Its very hard to find any store bought sandwich bread that doesn’t have it added as the second ingredient and even some of the 24 hour sourdough breads one purchases in the US. Hodgson’s Mills is the only White wheat flour I have been able to find in my city that doesn’t have it added, but there may be other flours. Plus, I like that their flour is unbleached and unbromated, which means less chemicals involved in the processing. You’ll have to let us know if any of your friends can track down the differences in the type of flour used, if malted barley is added to the bread flour and ingredients, or if they ate 24 hour sourdough breads made with natural yeast on the European breads. I’m sure many people would be interested to know their secret!!! BTW. Malted barley has tannins in it. Some have found that malted barley adds to migranes also. It may be for some, the inflammation is going to the GI tract vs causing migranes. Lots of factors to consider. This article also mentions European Crusty breads.

  • Casey

    This is fascinating! This could explain a lot as I tend to have the same symptoms (if not worse!) with “lactose-free” dairy. I was thinking it was the increased sugar in lactose-free products, but it could be this A1 casein. I’m in California and will try a2 Milk soon.

    Thank you for your research and for sharing. Excited to see what the geniuses at Monash find 🙂

  • Jamie Orr

    Thanks for the info. I have discovered that I do a lot better with A2 milk than with regular or lactose free. Any suggestions on a cheese made from cows higher in A2 protein?

      • Sadie Grant

        Interested in this topic of A1 and A2 milk since training in kinesiology and gut health. I am finding that those who are sensitive to wheat and related grain proteins are also sensitive to the protein in A1 milk but tolerate the protein in A2 milk (generally settling for goats milk as an alternative).

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