Main ingredients are:

  Oat Flour (110g)
  Maltodextrin (165g) 
  Brown Rice Protein Isolate (102g)
  Canola Oil (56g)
  Fiber (38g)

I'm worried about how much of that is Maltodextrin, as it's really just a chain of glucose molecules, and so would give an extremely high glycemic load. It's somewhat mitigated by the fiber, as fiber hampers sugar uptake in the digestive system, but it's still a lot. I'd like to see some proper data on the what the GI score of Soylent is derived from actually testing it properly.