Wikipedia says under Excess Protein "It is important to note here that contrary to popular belief, the consumption of dairy products does not prevent bone loss. In fact, the consumption of dairy products, as it is high in animal protein, creates bone loss. Whenever there is an increase in dairy consumption the rate of osteoporosis and bone fractures also go up."
Protein (nutrient) - Wikipedia, the free encyclopedia
Excess protein makes the body too acid. The body takes calcium out of the bones to neutralize this acid. Then the product is urinated out. Americans get plenty of calcium in their diet but a simple test shows that they have lots of calcium in their urine.
Reason 2 of why it is better to eat plant foods.