So food is "simple", yet obviously depending on the type and quantity of food eaten, we consume a different assortment and balance of nutrients. I don't think anyone can argue that there isn't a huge percentage of the population that does a bad job of managing that balance. If that's the case, then Soylent could help those people - more power to them.

If, on the other hand, the body is resilient, and we don't have to be that precise about what we eat (as in, just eat "reasonably healthy" foods and you'll be fine), then soylent should be a reasonable substitute, even if it isn't without flaws.

Either way, they should keep going with their plan - I wish them well.