They do have some fat, mainly in the form of unsaturated fat. They are low in sodium, unless soy sauce or other salty ingredients are added. Tofu can be a good source of calcium if a calcium salt is used in the coagulation process. Both tofu and tempeh can contain significant amounts of iron. Products which contain more than 3 milligrams of iron in a 3-ounce serving include Nate's Easy Tofu, Lightlife Quinoa Sesame Tempeh, and White Wave Sea Veggie Tempeh.
Many companies use organically grown soybeans for their tofu and tempeh.
White Wave may also use transitionally grown beans, but they state that the soybeans used have not been genetically altered in any way. While genetic engineering may increase yields and reduce costs, many environmentalists and scientists fear that this technology may be harmful to the environment and risky for our health. I recommend use of tofu and tempeh containing organically grown soybeans. Tofu and tempeh are perishable products and should be kept refrigerated, unless the tofu is in an unopened aseptic package. Once a tofu package is opened, leftover tofu should be covered with fresh water for storage and the water should be changed daily.