One thing from the link above that I didn't previously know: "The Soylent recipe is based on the recommendations of the Institute of Medicine (IOM) and is approved as a food by the Food and Drug Administration (FDA)." (emphasis theirs)

That triggers my bullshit detector.

FDA does not "approve as food". It has a list of substances which have been approved as food additives or are GRAS (generally recognized as safe, basically a grandfathering clause). I'm willing to believe that Soylent ingredients all come from that FDA-approved list. That does not mean that the FDA approved Soylent as food.