Sixty-five percent of people have trouble digesting regular milk. Lactose usually gets blamed for this widespread "milk intolerance," but lactose is only part of the problem. The other problem is a milk protein called A1 beta-casein.
A1-beta casein is the biggest problem food nobody's ever heard of. Studies suggest it causes digestive symptoms like gas, bloating, diarrhea, constipation, and stomach pain in a significant number of people.
Most regular milk contains A1 beta-casein because most cows have A1-producing European genes. But there's a fix. You can breed cows to produce a more digestible milk protein called A2 beta-casein, the original protein produced by cows. The milk from these specially-bred cows is called A2 milk. (By the way, Pioneer Pastures cows are A2 cows, and our milk protein shake is lactose and A1 beta-casein-free.)
Here's the big takeaway. Regular milk contains A1 and A2 beta-casein, but A2 milk contains only A2 beta-casein. Science suggests that A2 milk is easier to digest for some people and may be better for long-term health.
At Pioneer Pastures, we want more folks to drink A2 milk so the benefits ripple through society. It's why we got into this business.
Below, explore the digestive benefits of A2 milk and dive deeper into the research by clicking the links. You'll learn why regular milk causes gut issues for some and how A2 solves them.
Why Regular / Non-A2 Milk May Cause Digestive Issues
Two components of regular A1 milk give folks the most digestive trouble:
- Lactose
- A1 beta-casein
Lactose intolerant people lack the enzyme (lactase) that digests lactose, the primary sugar in milk. Without lactase, you can't break down lactose before it reaches the small intestine. When lactose reaches the small intestine intact, it meets gut bacteria that ferment this milk sugar, causing gas, diarrhea, and other GI symptoms.
Most people, including many doctors, blame lactose intolerance for all milk digestion issues. But many folks with so-called "lactose intolerance" don’t actually have problems absorbing or digesting lactose. And so, there must be another cause for milk digestion issues. That cause may be A1 beta-casein from regular milk.
Here's why A1 beta-casein may be problematic for some. When we digest this milk protein, it turns into another compound called beta-casomorphin-7 (BCM-7). (Digesting A2 beta-casein, by the way, doesn't create BCM-7.) The European Food Safety Authority flagged BCM-7 in a 2009 scientific report, noting its wide-ranging adverse effects on the gut and other organ systems. Since then, the scientific research against BCM-7 has continued to mount, especially in the realm of digestion in animal studies.
5 Ways A1 Beta-Casein May Impair Digestion
Regular milk contains A1 beta-casein, which you digest into BCM-7. BCM-7, in turn, may impair digestion via several mechanisms.
As you read this section, understand that most of this mechanistic evidence has been shown in animals, not humans. Human evidence suggests A1 beta-casein causes more digestive symptoms than A2 beta-casein, and researchers are still unraveling why. With this in mind, here are five possibilities based primarily on animal research.
#1: Reduced gut motility
Gut motility refers to the movement of food and fluids through your digestive tract. Proper gut motility keeps you regular and prevents food from lingering in the gut, fermenting, and causing gas, loose stool, and other symptoms.
Specialized "opioid receptors" in the gut control this system. BCM-7 interacts with these receptors, reducing gut motility. Opioid drugs have a similar effect, which is why these drugs cause constipation.
In a 2014 study, rats fed regular milk had reduced gut motility compared to rats fed A2 milk. A 2016 human trial involving 45 Chinese people had a similar finding.
#2: Increased inflammation
In this context, inflammation refers to an unnecessary, damaging immune response that causes digestive symptoms. The gut houses most of the body's immune cells, making it an inflammatory hub.
Mice given regular milk (or BCM-7 directly) showed higher levels of gut inflammation. These mice had more immunoglobulins, inflammatory cytokines, and white blood cells — markers of inflammation linked to digestive distress. Mice given A2 milk did not have these problems.
#3: Altered gut microbiome
The trillions of microbes in your gut (your gut microbiome) can either aid or impair digestive health. Everything you consume influences this massive colony.
In mice, drinking A2 milk led to a healthier gut microbiome vs drinking regular milk. Specifically, A2 mice made more short-chain fatty acids, beneficial compounds produced by gut bacteria. Conversely, regular milk drinking mice had more inflammation, possibly because the regular milk encouraged the proliferation of a family of bacteria called Ruminococcaceae.
Bottom line? We need human studies, but animal evidence suggests that A2 milk is better for gut critters than regular milk.
#4: Excess mucin production
Mucin is a protein that structures mucous (mucous lines your gut, lungs, and other organ systems). Proper mucin levels keep your gut running like a Swiss clock. Accordingly, too much mucin impairs gut motility and disrupts the balance of gut bacteria, causing digestive symptoms. In rats, the administration of casein hydrolysate (which contains A1 and A2 beta-casein) led to higher mucin production, though the effect wasn’t statistically significant. In the isolated rat intestine, BCM-7 administration increased mucin production, suggesting A1 beta-casein is to blame for the excess production.
#5: Lactose intolerance
Not everyone with milk intolerance has lactose intolerance. Some folks may react to A1 beta-casein instead. Others may react to both lactose and A1 beta-casein in regular milk.
Researchers believe BCM-7 from A1-beta casein may contribute to lactose intolerance via mechanisms we covered earlier:
- Inflammation may decrease lactase production
- Altered gut bacteria may affect lactose absorption
- Reduced gut motility gives lactose more time to ferment
Will switching to A2 milk cure lactose intolerance? Science hasn't answered this question, but it may be worth a personal experiment.
A2 vs. Regular Milk for Digestion: Clinical Evidence
The strongest evidence for A2 milk improving digestion comes from randomized controlled trials (RCTs), the gold standard of science.
In RCTs, researchers randomly assign human participants to experimental or control groups. This method reduces researcher bias while allowing science to test one condition vs another.
These RCTs looked at consuming A2 milk (experimental condition) vs. regular milk (control condition) to compare effects on digestion:
- 2024 RCT from the Journal of Cancer Prevention. Forty people who drank A2 milk for two weeks had less abdominal pain, diarrhea, stomach gurgling, and fecal calprotectin (a marker of inflammation) than when they drank regular milk for two weeks.
- 2016 RCT from Nutrition Journal. Forty-five people who drank A2 milk for two weeks had less digestive discomfort, better bowel motility, reduced inflammation, and enhanced cognitive function than when they drank regular milk for two weeks.
- 2014 RCT from European Journal of Clinical Nutrition. Forty-one people who drank A2 milk for two weeks had firmer stool and less inflammation than when they drank regular milk for two weeks.
The takeaway? The science strongly suggests that A2 milk causes fewer digestive issues than regular milk in some people.
Running Your A2 Experiment
A well-run human study doesn't prove that A2 milk helps you. You have to test it in the laboratory of your body.
If regular milk is bothering your gut, run an experiment. Switch to A2 milk for at least two weeks and note any changes. Are things running smoother down there? Do you have less gas, bloating, or stomach pain? If you answer yes to any of these questions, consider permanently switching to A2 milk.
It doesn't have to be a perfect experiment. If you've been avoiding dairy for years, you don't have to reintroduce regular milk as a control condition. Just try A2 milk and see how you feel.
A quick note. If you have a milk allergy (vs. milk or lactose intolerance), stay away from dairy products altogether, including A2 milk. Talk to your healthcare provider if you have questions or concerns. Allergies are serious business.
Assuming you don’t have a dairy allergy, it’s easy to bring A2 milk into your life. Pioneer Pastures makes the world's first ultra-filtered A2 milk protein shake that is also lactose free. It's a simple and delicious way to get more protein in a highly-digestible format. Getting more protein (from A2 milk or other sources) helps support muscle mass, hormonal health, and weight management. It’s a win-win.
Remember, our cows are special cows that only produce A2 milk. There's no A1 beta-casein to worry about. A better cow, a better milk.
The A2 Revolution is Just Beginning
The A2 revolution is just beginning. It will get much bigger.
Over half the world has trouble digesting milk. If we can change that number by a few percentage points, we could improve hundreds of millions of lives.
Start with your diet, though, because that's the only diet you have complete control over. Good luck with your A2 experiment.
