Casein is a protein that is found in milk and used independently in many foods as a binding agent. Technically, it is part of a group called phosphoproteins, collections of proteins bound to something containing phosphoric acid. It may also be called caseinogen, particularly in European foods.
A salt, meaning it has no net ionic charge, of the element calcium, casein has a number of interesting properties that make it useful in foods and cooking. Many people believe proteins are healthier if consumed when not denatured — one of the major lines of reasoning used in supporting a raw food diet. Denaturing occurs when a protein loses its inherent structure, due to high heat or acid for example, at which point it no longer acts in the ordinary manner. Casein, because of its structure, is not susceptible to denaturing.
Casein can be found in two main types: edible and technical. Edible casein is widely used in both medicine and food, both for nutritional value and as a binder. The technical type is used in an enormous range of products, including paints, cosmetics, and many types of adhesives. A significant number of people are allergic to this protein and may find themselves experiencing reactions both to food products and to products such as nail polish that contain it.
People with allergies or who are vegan, and therefore avoid animal products altogether, are not always aware of the prevalence of casein in foods. For these people, it is important to note that, although a product may be labeled lactose free, it may still contain casein for other reasons. Soy cheeses, for example, often contain protein derived from milk, which may stimulate allergic reactions in people who assume that they are dairy free.
Casein has also been linked to negative effects in people with autism. While in most people, this protein is easily broken down by the digestive system into peptides known as casomorphins, and then further processed into basic amino acids, some evidence suggests that in autistics, this process does not occur fully. The resulting casomorphins, which fail to break down completely, may have an effect on the body similar to that of morphine or other opiates. For this reason, some experts on autism recommend that people suffering from autism avoid products containing this protein.