Tofu or soybean curd is a food of Asian origin. Production of tofu involves soaking soybeans in water and creating soy milk, then curdling the milk using a substance such as calcium sulfate or lemon juice. The curds are separated from the whey and usually packaged in block form. Most tofu brands offer a range of soft and firm varieties, which differ mainly in the amount of water retained. Pressing tofu can remove additional water.
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Unlike most plant-based foods, soy is considered a complete protein, possessing all the essential amino acids. Tofu is thus a good protein source, due both to the amount and nature of the protein it contains. The protein content is higher in firm types of tofu than in softer types. According to the Illinois Center for Soy Foods (ICSF), a 3-oz. piece of firm tofu has about 13 g of protein, compared with about 4 g in soft tofu. The Vegetarian Resource Group (VRG) puts the content of 4 to 5 oz. of tofu at 11 g.
Nearly half of the calories in tofu comes from fat. Yet according to Rutgers Cooperative Research and Extension (RCRE), 3 oz. of firm tofu contains only 4 g of fat, and silken tofu contains half that. The ICSF puts the fat content of a 3-oz. serving in the range of 2 to 7 g. Both types of tofu are very low in saturated fat and do not contain cholesterol.
Isoflavones are phytoestrogens, a type of plant-based hormone.The Dana-Farber Cancer Institute credits the isoflavones in tofu with health-promoting properties. According to Rutgers, phytoestrogens can reduce the risk of osteoporosis, heart disease, and some types of cancer. The isoflavone content in tofu is about 25 or 30 mg per 3-oz. serving, according to ICSF.
Calcium sulfate is one of the coagulating agents used in the creation of tofu. Tofu produced with this method is particularly high in calcium content, providing about 6 to 15 percent of the daily requirement depending on the type of tofu. The Vegetarian Resource Group lists tofu as a good source of calcium for vegetarians and vegans, and explains that there is more calcium in a few ounces of tofu than in a cup of regular milk.
The carbohydrate content of tofu does not vary as greatly with the type of tofu as do other nutrients. A 3-oz. portion of firm tofu contains about 2 to 4 g while soft, silken tofu has 2 to 2.5 g. According to ICSF, the fiber content of silken versions is minimal, while that of firm tofu is nearly half the total carbohydrate content. Sugar makes up about half the carbohydrate content, according to RCRE.