I think fat soluble nutrients are little less straight forward then vitamin B/C and minerals.
I think it would be better to add those from natural sources to the soylent mixture.
There are so many different forms of those fat soluble nutrients, 8 different kind of vitamin E, many different kinds of carotenes, different kind of omega-3, different kinds of vitamin D etc. etc.
For example, I think this is a very good product:
2ml of this contains 4880 IU vitamin A, 1520 IU vitamin D. It also contains omega 3 (I’m not sure how much exactly, but should be enough). It also contains some vitamin K2 and CoQ10.
For vitamin E (Tocotrienol/ Tocopherol) and carotenes, I think red palm oil covers this complete range of nutrients. Red palm oil is quite expensive tough. I’m searching for a good concentrate.
I think synthetic version of vitamin B/C are fine. Minerals shouldn’t be a problem as well. What do you guys think?