Milk Allergy Explained

Working behind a cheese counter, we talk to our customers about the impact dairy products can have on health, be it as an important way to enrich and maintain your gut microbiome, or to help our customers understand the various issues with milk and cheese, such as milk allergies and lactose intolerance.

In this blog post, the focus is on allergies to milk and cheese.

Milk Allergy

To understand what a milk or cheese allergy is, we need to first understand the components of milk, and how they interact with our bodies.

Milk is made up of water, fats, proteins (caseins, antibodies, albumins, globulins), sugar (lactose), minerals (Calcium etc.), and organic compounds (e.g. beta-carotene and terpenes). If it is unpasteurized milk, it also contains a selection of microbes, which are reflective of the dairy environment and pastures. Pasteurized milk does not contain these microbes.

The proteins in milk are the allergens (things that cause an allergic reaction) in an overwhelming percentage of cases of milk allergy. There are a wide number of proteins found in milk, but these can be broadly separated into two classes: curd proteins (caseins) and whey proteins (antibodies, albumins, globulins). It is possible to be allergic to each of these proteins in both groups (see table opposite [adapted from Methods. 2014 66(1): 22–33. Cow’s milk allergy: From allergens to new forms of diagnosis, therapy and prevention.]), however 99% of cheeses (which are rennet set) contain only curd proteins, and so the majority of allergic reactions are against the curd proteins in cheese - since the whey proteins are lost during this method of cheesemaking.

The curd proteins found in cheese, which is formed from the action of rennet, are of 3 different types: alpha-s-casein, b-casein, and k-casein. In liquid milk, these three proteins are assembled together in massive soluble complexes, called micelles (shown below in the electron micrograph).

On coagulation of milk into cheese via the action rennet, these micelles coalesce into an organized structure (coagulum/junkett) which, when processed to curd, eventually forms the object of cheese. (If you want to learn more and see this in action, come to one of our cheesemaking classes!) Out of these three, allergy against alpha-s-casein is by far the most common.

An allergy is when someone's immune system is hyper-sensitive to objects which don't normally cause an immune reaction in the general population. The reaction is driven by proteins called antibodies, which can be envisaged as labelers of microscopic objects - and when these objects are labelled, or 'bound' by antibodies, they start an immune reaction (the swelling, the reddening, the heat, the pain), which can get out of control and manifest itself on the skin, in the stomach, or other areas of the body.

Research has identified the pieces - called epitopes - of the alpha-s-casein which is recognized by antibodies, and this allows us to figure out ways to deal the allergy.

The alpha-s-casein protein actually has two slightly different forms (called isoforms), which are coded by subtle variations in the DNA of the alpha-s-casein gene across the dairy cow population. These are called alpha-s1-casein and alpha-s2-casein. The amount of s1 or s2 in milk, also varies the different breeds of cattle - for example 96% of Guernseys have the alpha-s2 gene, compared to 25% of Holsteins and 33% of Jersey and Brown Swiss.

Alpha-s2-casein has been shown to contain less of these epitopes, and therefore is less allergenic. With this in mind, dairy farmers are now breeding their herds to enrich them for more alpha-s2-casein. But it is hard (and expensive) to quantify the prevalence of the s2 gene throughout a herd. So few farmers are able to provide solid numbers to help consumers make an informed decision.

Goat, sheep, and water buffalo milk and cheese, also contains alpha-s-casein proteins, although these cheeses and milks are less allergenic for tow main reasons.

Firstly, these animals tend to have more alpha-s2-casein genes throughout their species rather than alpha-s1-casein.

Secondly, the genes within these animals actually vary slightly in the genetic areas which code for the protein epitopes in the cow genes. This means that cheese from these animals is not as well recognized by our antibodies, and therefore is less likely to promote an allergic reaction than the regular cow's cheese.

Taking all this science together the bottom line is this, for those of you with a milk or cheese allergy:

If you have a cow's milk allergy, you may not necessarily have an allergic reaction to cheese - it depends on what protein you are allergic to in the milk.

Try sheep, goat and water buffalo milk and cheese. Due to inter-species genetic variation of the allergenic alpha-s1-casein gene, and the lower levels of alpha-s1-casein overall and higher levels of alpha-s2-casein, this will mean that you are more likely to tolerate these milks over cow's milk.

#dairy #milk