And, avoid foods high in oxalic acid. Oxalic acid will bind the calcium that is available in the food and make it so much waste. Here's a list of foods that contain oxalic acid and the amount per 100g.
http://www.nal.usda.gov/fnic/foodcomp/Data/Other/oxalic.html
Kale is nice and low on the chart; but, if you are already having calcium issues, adding it might not be a good idea. I'd avoid any oxalic acid containing plants all together until the calcium issue is overcome. But, that's me. I tend to be overly cautious....