For about a decade in my late teens and twenties, I avoided dairy products because I thought they would aggravate my irritable bowel syndrome. While typical grocery store cow’s milk still bothers me, I found that I can consume gallons of goat’s milk weekly without problems. The A2 beta-casein protein makes all the difference for me and many others, who want to consume dairy.
Digestive issues, including Irritable Bowel Syndrome (IBS), Irritable Bowel Disease (IBD), constipation, bloating, diarrhea, and intestinal discomfort have become increasingly common in the past several decades, with 61% of a 2019 study’s survey takers reporting a digestive issue within the prior week (1).
Digestive inflammation harms the body, calcium and milk prevent this
Digestive irritation increases the body’s production of nitric oxide, a free radical that in itself contributes to slower transit time (24, 27) and exists in higher concentrations in people with bowel diseases such as Crohn’s and IBD. Furthermore, intestinal inflammation typically means a compromising of our intestinal mucosal barrier, which, when damaged, leads to increased intestinal permeability, bacterial translocation, and an increased predisposition to develop problems like intestinal colitis and IBD (10, 21). Alterations in gut microbiota can lead to unfavorable changes in things like metabolic endotoxemia, oxidative stress, lipid peroxidation, and obesity (4).
To remediate these issues, people commonly eliminate foods known to cause digestive disturbance, including dairy- and gluten-rich foods. However, a decrease in dairy consumption can lead to a variety of issues, including bone mass loss and hypertension. Even children from mothers with higher prenatal calcium intake had lower incidence of high blood pressure (7). Further, one study found that people who ate the most dairy had the highest markers of cognitive function in all eight cognitive measures that the study used (8).
A2 beta-casein: better than A1
So, how can we gain all the benefits of dairy and calcium, while avoiding the harms of intestinal inflammation and mucosal disturbance? A growing amount of research suggests that consuming milk with A2 beta-casein, rather than the commonly consumed A1, can help many people avoid dairy’s risks while retaining all of its benefits.
About 81% of the protein in cow’s milk consists of casein, a protein made up of over 200 amino acids in a chain. 30% of the total protein comes from beta-casein, one of the four types of caseins. While A2 beta-casein has an amino acid called proline in the 67th spot on the chain, a mutation in some cow breeds about 5,000-10,000 years ago changed the 67th spot from proline to histidine, leading to the A1 beta-casein strain. That means A1 and A2 casein differ by one amino acid, proline or histidine, at spot number 67 on the amino acid chain (23). However, upon interaction with enzymes in our digestive system, the histidine allows a smaller chunk of the protein, called a peptide, to cleave off. The consumption of A1 beta-casein, but not A2 beta-casein, releases the opioid peptide Betacasomorphin-7 inside our digestive system (19). Conversely, A2 beta-casein released no BCM-7 at all (20).
BCM-7: A1 beta-casein’s potentially harmful peptide
Each analogue from BCM-7 displayed opioid activity in animals (3), indicating its role as an opioid agonist, which offers an explanation as to why it causes trouble in some organisms’ digestive systems. Our intestines and colon contain clusters of opioid receptors (31, 28) that play critical roles not only in our digestive function, including bowel motility and formation, but in our mood and cognitive function (16).
BCM-7 has exhibited a variety of inflammatory and harmful effects in studies, including an inflammatory immune response in the gut (25), modulation of the mucosal immune system (9), a slowing of digestive transit time (17), and a sharp rise in immunoreactive discharge in the digestive system (6). Since the intestinal mucosal layer’s function intertwines closely with immune system function and the bacteria in the gut, these immune and mucosal disruptions offer an explanation why some studies (14) find that cow’s milk has a constipating effect, compared with soy milk alternatives. Additionally, A1 beta-casein, and the resultant BCM-7 that cleaves from it, has shown to double the prevalence of type-1 diabetes over a span of three generations (5).
A2 beta-casein shows favorable effects on the gut
A2 milk, with a proline amino acid at spot 67, that limits the amount of BCM cleaved and released into our bodies (26), has shown to have much more benign effects on our digestive systems. One study found people with poor milk tolerance to report fewer symptoms of abdominal pain, flatulence, and diarrhea with milk containing only the A2 beta-casein (18). Another study found both lactose absorbers and malabsorbers, when consuming A2 beta-casein milk compared to A1, to have significantly lower negative symptoms of abdominal pain, bloating, stool frequency, and stool consistently for at least 12 hours after consumption (12). Rats consuming A1 milk had significantly longer transit time than rats consuming A2 milk, an effect attenuated by the opioid blocker naloxone, which indicates the longer transit time stemmed from BCM-7’s opioid effects (2). In that same study, A1-treated rats also had higher levels of colonic myeloperoxidase, an inflammatory marker often elevated in people with heart disease.
When consuming A2 milk, instead of A1, people with self-reported intolerance to traditional cow’s milk demonstrated significantly lower post-dairy discomfort scores, improved overall gastrointestinal function, lower concentrations of inflammatory markers in the feces, faster transit time, and fewer adverse events overall (15). The same study found evidence of increased digestive issues in the A1 group over the A2 group, regardless of lactose intolerance or not. Although A1 milk commonly causes constipation, in some people it causes diarrhea, in addition to the typical gut inflammation, abdominal pain and bloating (13). It seems that the inflammatory, opioid-agonizing properties of BCM-7 can cause either diarrhea or constipation, because in this study, people drinking A2 milk reported none of these digestive issues. In women with dairy intolerance, A2 milk attenuated a rise in breath hydrogen caused by A1 milk (18), indicating that A2 milk caused less bacterial feeding in the intestines.
Gut health translates to emotional health
The significance of intestinal inflammation caused by A1 milk (11) goes beyond gut discomfort, causing behavioral and physiological effects in the brain as well. Study participants drinking A1 milk have demonstrated worsened cognitive ability compared to those drinking A2, evidenced by slower response times (15). The consumption of casein containing a mixture of A1 and A2 led to decreased opioid receptor binding in animals’ brains, including the hypothalamus and amygdala, but the consumption of purely A2 milk did not cause any changes in opioid receptor binding (22). Illustrating a grander behavioral and cognitive effect, animals in this study drinking A1/A2 mixed casein-rich milk displayed significantly increased immobility time, indicative of depression, compared to animals with casein-free groups.
How to find A2 milk at the store
Many people who believe they have lactose intolerance might actually have reacted negatively to the A1 beta-casein and its BCM-7 peptide. For those who want to retain the multitude of benefits, physiological and cognitive, offered by milk and calcium, A2 milk deserves a shot. According to Dairy Australia, Guernsey Cows contain the most A2 casein, but Holstein, Guernsey, and Brown Swiss cows still contain a high proportion of A2. Conversely, Ayrshire and Red and White cow breeds contain the least A2 casein and the most A1. Goat milk and sheep milk contain just the A2 casein, no A1 at all, so those two offer the safest choice when you visit the dairy aisle. Personally, I cannot tolerate any A1 cow’s milk, but I tolerate goat’s milk perfectly, with no issues.