While getting enough calcium in the diet helps improve bone density, too much phosphorus or protein can damage bone density, according to an October 1993 study published in “The American Journal of Clinical Nutrition.” Because calcium is involved in the metabolism of both phosphorus and protein, eating more phosphorus than calcium seems to increase the risk that your body will leach stored calcium from your bones to maintain blood calcium, thus increasing your risk of osteoporosis.
Firm Tofu -- Calcium Sulfate
Firm tofu made with calcium sulfate has the highest calcium content as well as the highest calcium-phosphorus ratio among types of tofu. According to the USDA National Nutrient Database for Standard Reference, 1/2 cup contains 861 mg of calcium and 239 mg of phosphorus, a ratio of about 3.6 to 1.
Regular Tofu -- Calcium Sulfate
Although regular tofu made with calcium sulfate contains considerably less calcium than firm tofu prepared in the same manner, the ratio is almost exactly the same. Regular tofu contains 434 mg of calcium and 120 mg of phosphorus per 1/2 cup, a ratio of about 3.6 to 1.
Other Firming Catalysts
Tofu that is not made with calcium sulfate does not contribute significant amounts of calcium to your diet. Moreover, these types of tofu may actually have a calcium-phosphorus ratio that is tipped in favor of phosphorus. For example, extra-firm tofu packaged aseptically and made with gluconolactone instead of calcium sulfate contains a mere 26 mg of calcium and 129 mg of phosphorus -- a 0.2 to 1 ratio.
Tofu for Protein
Tofu shines as a stand-in for all kinds of other protein foods. Because many foods high in protein, such as meat and eggs, are also high in phosphorus, using tofu as an entree instead of meat or eggs a few times per week can have a significant impact on your overall calcium-phosphorus ratio and on your bone density. For example, two eggs contain 58 mg of calcium and 204 mg of phosphorus, a 0.28 to 1 ratio. Replacing the eggs with scrambled tofu a couple of times weekly helps invert the ratio in favor of calcium instead of phosphorus. A single beef flank steak also contains 58 mg of calcium, but 817 mg of phosphorus. That's a ratio of 0.07 to 1. Stir-fried tofu and vegetables would make a flavorful and calcium-positive substitution.
References
- "The American Journal of Clinical Nutrition"; Intakes of Calcium, Phosphorus and Protein and Physical Activity Level are Related to Radial Bone Mass in Young Adult Women; Jill A. Metz, et al; October 1993
- "The American Journal of Clinical Nutrition"; Dietary Calcium, Protein, and Phosphorus are Related to Bone Mineral Density and Content in Young Women; Dorothy Teegarden, et al.; September 1998
- Office of Dietary Supplements, National Institutes of Health; Dietary Supplement Fact Sheet; Calcium; June 2011
- USDA National Nutrient Database for Standard Reference
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