Soybeans contain 35 to 40 percent protein. These soybean proteins are "complete," which means they contain significant amounts of all the essential amino acids our bodies need but cannot make on our own. That is why soy protein can be a great substitute for animal-based protein, which also has complete proteins but contains more fat. The fat in animal protein is especially unhealthy because it is saturated fat (the "bad" kind of fat), combined with cholesterol.