There are conflicting opinions when it comes to dairy; I mean, Milk does the body good right? We live in a country that eats more calcium than any other population yet also as the highest occurrence of osteoporosis. Something doesn't seem to add up in this scenario. So let's break it down, do you need to have diary in your diet? And if you remove it how do you get enough calcium and other vitamins - like Vitamin D that most milk is fortified with?
Milk has a low glycemic response but, it has an unproportionally high insulin response. Dr. Loren Cordain (who authored the Paleo Diet and continues to do much research in the area of Paleolithic nutrition) says that consuming milk has an insulin response similar to eating a chocolate chip cookie or candy. So milk adversely raises insulin in your body and can contribute to overall metabolic derrangement and insulin resistance. Some people are lactose intolerant which means they are unable to properly digest the lactose (carbohydrate) found in milk. People's ability to process lactose decreases after age 4, when the enzyme to digest lactose is down regulated since you are now old enough to be able to get your norishment from a source other than milk, some people's enzyme downregulates to the point where they no longer can comfortably consume dairy products since they are lactose intolerant.
What about the protein in milk, protein is good for me right? The protien in milk is called Casein, which is often whata is found in most nutritional protein powders used for post workout recovery. Casein is similar to Gluten found in grains which is the "grain protein" and like gluten casein also causes gut irritation/leaky gut syndrome which leads to inflammation in the body and can contribute to autoimmune disease. What exactly does "leaky gut" mean? There are certain things in food like gluten and casein that actually create small tears or perferations in the lining of your gut while you are digesting it. Over time with frequent exposure your body is unable to keep up with the repair of these tiny perfereations, and things can leak out of your gut and into your blood stream that would normally be too large to pass through the lining. When things pass through, even if they are not harmful, your body attacks it because it identifies it as a foreign object which creates inflammation in your body and diverts your body from attacking the real foreign objects that need to be attacked.
Note that the inflammatory effect caused by the increased insulin response and the leaky gut syndrome also effects acne, especially in people who are already acne prone. Many people find that their complexion clears when they switch to a Paleo diet and remove grains, legumes, and dairy from their diets. I've found that eliminating dairy (with the exception of butter) has greatly improved my complexion - something I've been struggling with since middle school. People that are acne prone seem to be particularly sensitive to both dairy and sugar, so two things to experiment with if you are looking for a clearer complexion. In additon to clearer skin, some other things you may notice when you cut out dairy are reduced symptoms of allergies and consgestion and even asthma.
So we've covered milk and how its components affect your body, but how does cheese fit into this picture? Dr. Loren Cordain says that cheeses do not cause the high insulin response as does milk, yogurt and other fermented dairy products, but is one of the most acidic of all foods. Paradoxically, despite its high calcium content, its net acidic load promotes calcium loss from the bones in order to balance the body's acid/base ratio. Calcium is leached from the bones when acid levels are too high in the body, depleting the purpose of eating cheese for calcium since your body is unbale to absorb most of it. Many people find that when they cut dairy out of their diets for a few weeks they feel better and notice that they do better without dairy. If you are going to continue having dairy, go for a full fat option like grass fed butter or raw milk from a local farm. I have found that when I do eat dairy if I eat goat cheese or feta cheese (from sheep) I get less of an inflammatory response than if I eat dairy from cows.
Like they used to say on Reading Rainbow, "But you don't take my word for it...." here are some other opinions and some more information about dairy.
Mark's Daily Apple - The Definitive Guide to Dairy
Whole 9 - The Dairy Manifesto