Soylent is not intended to diagnose, treat, cure, or prevent any disease. FDA be damned, people are actually allowed, with great level of discretion, to choose what they eat. There are controls on what they can put it in, it must have an accurate ingredient list, a nutritional label, etc., but medicine it is not.
Soylent is intended to prevent malnutrition. It is advertized as fullfilling _all_ of your nutritional needs. (Why would they call it Soylent? The name comes from a sci-fi movie where Soylent is a food made from human corpses. Using that name is an indication that there is a lack of judgement in the Soylent team.)
Prevention of malnutrition is not the same as treatment of nutritive deficiency diseases. Prevention of malnutrition is more simply termed "eating food".
Products like Soylent or Plumpynut are foods, not drugs. Replacing one's entire diet with Soylent is logically equivalent to choosing to eat a banana rather than an apple with your lunch today.
If you have kwashiorkor or beriberi or scurvy or pellagra, it is unlikely that you could be effectively treated with Soylent, because it is formulated to satisfy daily needs, rather than to correct a deficiency that may have taken many months to manifest symptoms. It is designed to be a complete food, using a recipe.
And if you watched the movie (it doesn't hurt all that much), you would know that only Soylent Green was made from people, rather than algae, as was claimed. The Soylent company sold other types of food products, and everyone ate mostly Soylent-brand foods, because they could not afford anything better. In the film, all the extras got most of their nutrition from Soylent Orange or Soylent Blue, or whatever those grubby-looking flakes were in the bins. Soylent Green always sold out early, and was in short supply.
Still... not the best naming decision. Most people haven't seen any more of the movie than the scene where Heston cries "You've gotta tell 'em. Soylent Green is people!"
