Foods high in oxalates include spinach, rhubarb, beet greens, and almonds. The calcium in spinach or rhubarb is almost completely unavailable. Legumes, such as pinto beans, navy beans, and peas, are high in phytates. The calcium in legumes is only half as available as the calcium in milk. You can reduce the phytate level in beans or legumes by soaking them in water for several hours, discarding the water, and then cooking them in fresh water.
Wheat bran is also high in phytates.
Wheat bran is the only fiber-rich food that appears to reduce calcium absorption. The fiber in fruits, vegetables, and common cereals does not significantly interfere with calcium absorption. To derive the maximum benefit from your calcium-rich foods, do not eat them at the same time as foods high in oxalates and phytates. If you wish to eat foods from these categories, eat them one hour before or two hours after calcium-rich foods. Excessive protein and sodium intake can increase calcium loss through the kidneys.