While people can absorb about 30% of the calcium in dairy and fortified foods (such as orange juice, tofu made with calcium sulfate, and soy milk), absorption is about twice as high from certain green vegetables, such as broccoli, bok choy, and kale. Much less calcium is absorbed from foods with high levels of oxalic acid—spinach, collard greens, sweet potatoes, rhubarb, and beans—and eating spinach with milk, for example, also reduces the calcium you can absorb from the milk. The calcium in foods that are high in phytic acid—whole grains, wheat bran, beans, seeds, nuts, and soy isolates—is also poorly absorbed, but these foods do not block absorption from other calcium-rich foods like milk.
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