There are several chemical components of milk that can cause certain individuals to react negatively -- through digestive difficulties or other symptoms -- to dairy consumption. Those who are lactose intolerant can not digest the sugar in milk. Casein is a protein in milk, and it, too, can cause some individuals difficulty.
Lactose Intolerance
If you're lactose intolerant, you do not produce the enzyme lactase, explain Dr. Reginald Garrett and Dr. Charles Grisham in their book "Biochemistry." Lactase is a chemical that helps your intestine break down lactose, the sugar in milk, so that you can absorb the chemical components of the sugar into your bloodstream. If you are lactose intolerant, the lactose in dairy passes undigested into your lower intestine, where bacteria break it down. This produces large quantities of gas, leading to bloating and cramping.
Casein and Allergies
Casein is another component of milk, but it's quite distinct from lactose. For one thing, casein is a protein, not a sugar. Most people who are lactose intolerant can handle casein without any difficulty. If you're allergic to casein, you can't drink milk or eat dairy products, even if you're lactose tolerant. Furthermore, while it's possible to modify dairy so that it doesn't have lactose in it -- making it appropriate for lactose intolerant individuals -- there is no such modification for removing casein.
Symptoms
If you have symptoms upon consumption of milk or dairy products, you may be lactose intolerant, allergic to casein, or both. One way to determine which component of milk you're reacting to is to see a doctor, who can test you for casein allergy. Additionally, however, you can determine through your observations which of the components you are sensitive to. Lactose intolerance always causes digestive difficulty, while allergies often manifest through hives, itching or respiratory difficulties, explains MayoClinic.com.
Foods To Avoid
Once you know whether you're lactose intolerant, sensitive to casein, or both, you can find alternatives to dairy that will allow you to enjoy your food without symptoms. For the lactose intolerant, there are lactose-free milks and milk products. These contain casein, so they're not appropriate for you if you're allergic to casein, but they don't contain lactose. Alternately, if you're allergic to casein, you likely need to avoid all animal milk. Soy milk, almond milk and other milk alternatives are casein-free.
References
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- MayoClinic.com: Milk Allergy
