Milk is frequently demonized on Facebook and Instagram by dieters, “nutritionists”, and supposed “advocates” of “eating clean” (whatever that means)… So if you’ve never herd (get it?) of A2 milk, or don’t know what it is, let’s have a candid conversation about the controversies of cow milk.

First thing to note is not all milk is equal when it comes to your tummy (and by tummy, I mean gastrointestinal tract.)

Let’s be clear, the posts and quotes disparaging milk are seldom backed by any real science. The food doctors of the world (us dietitians) continue to recommend the consumption of animal milk due to its richness in vitamins, minerals, and protein.

What if I told you there’s a certain protein in many conventional cow milks that may cause your stomach trouble? Research (keep reading) explores symptoms like bloating, abdominal pain, diarrhea, watery stools that aren’t quite diarrhea, increased gut transit time, and even cognition that are impacted by milk.

So here’s the science in semi simple terms:

  • Most commercial cow milks contain two protein variations: A1 and A2 beta casein
  • The A1 and A2 proteins vary only slightly in their chemical makeup but have very different consequences following digestion
  • When digested, the A1 protein is broken down to produce what’s called “beta casomorphine 7” (BCM-7)
  • A2 is resistant to this breakdown and stays in tact (this is a good thing)
  • The beta caseins present in human, goat, sheep, and buffalo milk are classed as “A2-like” meaning they are not broken down into BCM-7 (this is a good thing)

Ok, that’s the protein side of things. Now you need to know what BCM-7 is and does:

  • BCM-7 attaches to mu-opioid receptors
  • Mu-opioid receptors influence gut transit time
    • Let me interrupt myself for a second, you know how opioid drugs like codeine can cause constipation? BCM-7, similar to codeine, results in slower transit time through the gut (this is not a good thing)
  • BCM-7 increases mucus secretion

Think of the two proteins (A1 and A2) as trucks, each with two trailers attached to them. As the A1 truck is getting on the freeway (being digested) the second trailer breaks off (remember, your GI tract breaks down the A1 protein.) In this scenario, the breakaway trailer is now rogue on the freeway and will slow down oncoming traffic. The A2 truck stays in tact when it gets on the freeway (is not broken down during digestion) thus does not slow things down.

Righto, we’ve covered the groundwork. Let’s get to the juicy stuff. How can your choice of cows’ milk cause your body chaos? Some recent research found:

  • Milks containing both the A1 and A2 proteins (mixed milks) caused worsening of GI symptoms (pain, bloating, diarrhea, watery stools)
  • Mixed milks were associated with significantly:
    • Increased colon transit time (the A1 trailer slowing things down)
    • Increased whole gut transit time (the A1 trailer slowing things down)
    • Increased concentrations of inflammation-related biomarkers
    • Decreased production of gut short chain fatty acids (these are favorable byproducts of bacterial fermentation in the gut, they have anti-inflammatory effects and enhance colon cell function… Decreasing them isn’t a good thing)
    • Longer responses and increased error rates on subtle cognitive impairment tests (most likely related to increased inflammation-related markers associated with mixed milk consumption)
  • Subjects with diagnosed lactose intolerance:
    • Had significantly worse symptoms following consumption of mixed milks
    • Had no worsening of symptoms when consuming A2-only milk (about the same as when they consumed no dairy… That’s huge!)

So let me interrupt myself again to translate these findings:

People often blame their stomach/GI symptoms from milk on lactose intolerance, however, this research suggests that such symptoms are not lactose intolerance, but a result of the A1 protein being digested into BCM-7, and BCM-7’s flow-on effects which ultimately have negative impacts on gut functioning.

What can you do?

Start drinking a milk that is not a “mixed milk”. You want a milk that only contains the A2 milk protein. The A2 Milk Company was founded back in 2000 in New Zealand and has a patent on a DNA test that ensures their dairy cows only produce the A2 protein. The test simply sequences a strand of tail hair. The A2 Milk Company now sells A2 milk in Australia, the UK, China, and the USA. You can read more on their website and find an outlet near you.

Disclosure: I received no compensation, sponsoring, financial incentive, or other inducements to write this article. I think the science here is fascinating and I see a potential group of milk-avoiders getting back on the milk bandwagon. I myself switched my family to A2 milk in June 2016 and have seen a huge change in our GI health as well as family and friends who have tried it. I own a small number of shares in the A2 Milk Company.

If you’re ready to get into the Mini Meals Mindset at snack time, sign up below for my Snack Staples List and join my NIFTY community (NIFTY = Nutrition Info + Feeding Tips for You!)


Hi, I'm Thalia the Dietitian 👋 I help parents overcome picky eating challenges, conquer mealtime battles and raise happy & healthy eaters. My unique approach to parenting at mealtimes uses elements of the “division of responsibility”, but goes even further when it comes to restricting (or not restricting) foods like dessert. I help parents through my courses and 1-1 coaching program approach mealtime situations from a place of respect, curiosity, and understanding to achieve their desired results. It’s my belief that every child deserves a healthy relationship with food, and every parent can give this gift to their child. I have a Master’s Degree in clinical nutrition and dietetics and I'm mum to two little ladies (and a retired guide dog lab.)


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