In the American diet, dairy foods are the primary source of calcium. Plant foods can also be a good source of dietary calcium, especially those such as as broccoli, kale, and bok choy; other plants high in calcium such as spinach, rhubarb, and beans may have lower bio-availability of calcium due to compounds called oxylates and phytates. Because the calcium content of common plant sources is rather low, it is diﬃcult for most Americans to meet their requirements exclusively from these foods. Individuals who choose not to eat dairy products should therefore try to include calcium fortiﬁed foods or supplements in their diet in order to meet recommendations, and they should limit salt, protein and caﬀeine, all of which decrease calcium retention.
American Journal of Clinical Nutrition. September 1999;70(3 suppl):543S–8S [Weaver CM et al.]