Do you suffer from post-dairy digestive distress, or “PD3”? A majority of people around the world avoid all dairy products due to lactose intolerance. But recent findings suggest there may be another reason why some people feel ill after ingesting milk: the milk protein beta casein, particularly the A1 form. This is the form most commonly found in the U.S. milk supply, and some research suggests it is not well tolerated. Another form of beta casein, called A2, while less prevalent in American dairy, seems to be better tolerated by many. There is also some research correlating A1 milk with increased inflammation and disease risk, such as heart disease and Type 1 diabetes. While research seems to be in the early stages, there is enough to at least give pause when considering which type of milk, if any, to consume.

Many self-diagnose with lactose intolerance for good reason: About 75 percent of the world’s population lacks enough of the enzyme lactase to properly digest the milk sugar lactose. In other words, this is the norm on a worldwide scale. The ability to digest lactose varies greatly depending on ethnicity, with the majority of those of African, Asian, Mexican, and Native American heritage having lactose intolerance. Symptoms include gas, bloating, stomach pain, cramping, and/or diarrhea about a half hour and up to two hours after consuming lactose. Those of Northern European or Mediterranean origin tend to hold onto their lactase enzymes and can often digest milk more easily.

The casein in milk has now come under scrutiny as a possible cause of gastrointestinal distress. There are two main proteins in dairy: casein and whey. Milk is roughly 80 percent casein. There are several different caseins, but those being studied are the beta caseins, particularly A1 beta casein and A2 beta casein. Most milk in the U.S. contains both A1 and A2, of which Holstein cow’s milk is the most common. Holsteins have been bred to produce higher volumes of milk with lower fat content. Brown cows such as Guernsey cows, on the other hand, and sometimes, but not always, Jersey cows, contain all A2 casein. Goat and sheep’s milk is always A2. Interestingly, dairy herds in Asia, Africa, and parts of Southern Europe are more likely to produce only A2 milk.

The difference between A1 and A2 casein is only one amino acid. However, this amino acid in A1 milk produces a peptide called beta-casomorphin, or BCM-7, when the casein is cleaved during digestion. The BCM-7 protein fragment often stays intact in the digestive tract. Some studies attribute the negative effects of A1 milk to this BCM, which can have opioid-like effects in humans. Potential negative health effects include increased inflammatory markers that can lead to gastrointestinal pain as well as increased GI transit time. Another small human study revealed digestive distress, increased GI inflammatory markers, as well as reduced cognitive processing speeds.

In addition, some studies attribute BCM to immunosuppression. For example, one study examined the rates of A1 versus A2 milk consumption among different populations and found that those consuming more A1 milk saw a greater incidence of Type1 diabetes. This type of diabetes is an autoimmune disease, so immunosuppression plays a role. This study could not prove causation, however. Lastly, one observational population study saw a strong correlation between intake of A1 casein and risk of atherosclerosis and cardiovascular disease. There has also been some correlation between A1 milk and schizophrenia, autism, and Sudden Infant Death Syndrome, or SIDS. More research is needed.

If you are someone who reacts negatively to milk and you are interested in doing an experiment, you may wish to try an elimination diet. For a period of time, consume only A2 dairy products and see if your symptoms resolve. There are a few ways to decipher if a particular milk product contains A2 casein. If it is a local product, ask the farmer what the herd is — is it A2 only, or a combination of A1 and A2? You are looking for A2-only milk. Another way is to look at the package. Do they have pictures of Holsteins or Jerseys on the label? Though this method is not foolproof, you are looking for brown cows, not black and white. Another option is to consume only sheep’s milk and goat’s milk, which are always A2. Cream and butter contain very little casein, while ghee contains next to none. They should be tolerated even if you have a casein sensitivity, though you may wish to avoid them during your elimination diet.

If after a trial elimination you have no gastrointestinal distress, then you do not have lactose intolerance, but rather an A1 beta casein intolerance. You will have to avoid A1 milk to keep your symptoms at bay. This, as some of the above research suggests, may not be a bad thing after all.

The information provided in this article is intended for general use only and is not to be used in place of medical advice from a licensed health professional.