In the early 1900’s soy was used as fertilizer; the high nitrogen content made the soy plant a valuable additive to soil. But then soy graduated to animal feed due to its protein content, and then later soy meal was used for industrial process: paper coatings, and fire-fighting foam. One company, Central Soya, figured out ways to process the beans which led to a wide range of food components: candy manufacturers used it to prevent their products from sticking to wrappers, General Mills incorporated it into non dairy deserts and puddings. Meat companies used it as a filler or extender in their bologna, salami, ham, and turkey slices. Supplement companies turned to soy protein because it was inexpensive and readily available. Soy protein, it turns out, has become the perfect canvas for food scientists to work with because it is so malleable.
The process of making soy protein or soy protein isolate begins after the oil has been extracted, and starts with removal of the fiber. The flakes, now devoid of fiber, are mixed with water, which is spun off in centrifuges. Then the water and soy are sent to an acid tank where they mix with hydrochloric acid, and then centrifuged again to get rid of the carbohydrates. Hydrochloric acid is highly corrosive and is used industrially to remove rust or iron oxide from metals and to dissolve rocks in order to release petroleum and natural gas.
The result of this process is a slurry (thick, yellow, and foamy) whose aroma is akin to a cattle feedlot, and is described by some as smelling like aging meat combined with old wet socks. The slurry is sent to be neutralized with sodium hydroxide (a chemical that causes blindness if it gets in your eyes, and is the active ingredient in Drano) and finally spray dried. Mixed with other ingredients, this soy protein or soy protein isolate has less than desirable flavor, so soy making agents (flavorings that neutralize the odor) are then added.
By the time the soy protein or soy protein isolate is in the feed or supplement or food all of the fiber, fats, and vitamins have been processed out, as well as the phyto nutrients. Soy protein or soy protein isolate may have protein, but in a less than bioavailable form, than eating tempeh or tofu. However if you compare the nutritional vacancies of soy protein, with say, a hamburger, the hamburger in comparison looks more like a Brussels sprout in nutritional value.