An interesting article in Healing Cancer Naturally discusses the bio-availability of calcium and other minerals, and makes an interesting point about calcium and no fat dairy:
"Calcium: won't absorb as a calcium supplement. That's because it needs both fat and fat-soluble vitamins to become bioavailable. So "no-fat" dairy, e.g., is the second surest way to clog one's kidneys with insoluble calcium, "second" only to taking a supplement with a glass of water, that is... None of the calcium ingested in this manner will make it to the bones, or anywhere else it's needed. But a cup of cottage cheese from whole (no fat removed!) and otherwise unmolested milk will deliver the kind of "live," so to speak, calcium that will do its job. It's "live" because fat and fat-soluble vitamins (and who knows what else!) in a substance where all of them occur together in proportions and amounts that are specific, as part of "natural solvents" that are specific -- all of these factors "enliven" this otherwise "severely wounded" (for purposes of bioavailability) calcium, and it gets a chance to become part of the live human body upon ingestion, rather than clog some organ or other with its dead weight".
from Elena Berezetsky, a technical/science writer