The way I see it is that so many people get by on nutrient-low, unbalanced diets that it's impossible to know exactly what the optimal combinations of food to eat really is. Humans are pretty resilient.

I doubt Soylent will be better or worse for you than the diet of a typical HN user if taken in the long term. Time will also tell: if after 5 years no adverse health effects are reported after a sufficient number of heavy users begin drinking it, then that's probably as best a "green light" as one could ever get.