I see you hold strong opinions (I am very critical of Soylent myself), but it might be wise to re-visit the evidence for some of your strongly-held assertions --otherwise you might end up misinforming others, and yourself.
For instance, what you say about 'NEVER supplement[ing] with iron' is quite wrong. Iron deficiency anemia is quite common, especially for young women; and it is routinely treated by iron supplementation [1], even over-the-counter: if anything, iron's bioavailability in adults is very low, and it is difficult to exceed safe levels (although it's the opposite for children) [2].
Also Vitamin D2 is not useless at all. Even though some recent studies have shown some limited evidence that D3 is stronger and longer-acting; decades of clinical practice have shown the safety and efficacy of high-dose D2 in treating severe vitamin D deficiency [3]. It's disingenuous to say otherwise.
And... what you say about Vitamin K1 vs K2 is also far from well-established. Putting aside the fact that actual clinical vitamin K deficiency is extremely rare in the first place, K1 is the most commonly used form for a reason: even though there has been some recent work indicating possible differences in bioavailability and function on the part of K2; current knowledge is still very limited, and there is not enough evidence to displace K1 as the main formulation approved for dietary supplements [1,2].
I could go on and on with other inaccuracies in what you said, but you get the idea.
Also be careful with overdoing that liver with onions habit. Even though animal river is very rich in iron and copper (which likely explains part of how you feel after eating it); it also happens to contain high amounts of vitamin A in retinoid (retinol) form, which as you correctly point out should be taken in moderation due to their much higher bioavailability vis a vis carotenoids, thus increasing its potential toxicity [7].
I should have pointed out that we are talking about healthy subjects here. People with anemia should take iron supplements. I am with you here. Same for people with severe vit D. deficiency. In this case, any form of vit. D will benefit them.
Thanks for the advice about the liver. I only take it once a week and a very limited amount (maybe 70-80 grams). In this case, my main course if basmatic rice with the liver for some fantastic flavoring.
Sure! As long as that's not polar bear liver [1]; you be mindful of other unlikely dietary sources of unusually high retinol content like sweet potatoes, pumpkins or cod liver oil [2]; and keep up with regular check-ups; you'll surely avoid hypervitaminosis A.
Case in point to show how I use supplements: My kids won´t take liver, no matter how hard I try to "hide" it. So, I give them 1/4 teaspoon per week of cod liver oil (green pastures, fermented).
Again, it´s not the supplements; it´s the product.
Regarding vitamin D, I would add that the only way to make sure your vitamin D level is sufficient is to get tested. Relying on the DRI alone will leave some people insufficient. I expect that many Soylent users will be insufficient and maybe deficient in vitamin D, not because of any failing on Soylent's part, but because this is already true for a random selection of the non-Soylent-using population. Dark-skinned individuals, obese individuals, and people with very little sun exposure (or living at a high latitude) are more likely to be deficient.
Practically speaking, this means: during your next annual physical, make sure your doctor tests your vitamin D along with your other bloodwork. The correct test is called 25(OH)D. Your insurance should cover it. (I am making an assumption about how privileged most HNers are.) Aim for a blood level of 30-40 ng/mL. <20 ng/mL is deficient, >=30 is sufficient, while >40 is probably pushing it, i.e. observational studies suggest that mortality starts to increase slightly around that point. A level greater than 50 ng/mL is almost certainly excessive, though still not close to toxicity. Some people argue for supplementing enough vitamin D to achieve higher blood levels (>40 ng/mL), but IMO the evidence doesn't support doing this and it might be harmful.
For instance, what you say about 'NEVER supplement[ing] with iron' is quite wrong. Iron deficiency anemia is quite common, especially for young women; and it is routinely treated by iron supplementation [1], even over-the-counter: if anything, iron's bioavailability in adults is very low, and it is difficult to exceed safe levels (although it's the opposite for children) [2].
Also Vitamin D2 is not useless at all. Even though some recent studies have shown some limited evidence that D3 is stronger and longer-acting; decades of clinical practice have shown the safety and efficacy of high-dose D2 in treating severe vitamin D deficiency [3]. It's disingenuous to say otherwise.
And... what you say about Vitamin K1 vs K2 is also far from well-established. Putting aside the fact that actual clinical vitamin K deficiency is extremely rare in the first place, K1 is the most commonly used form for a reason: even though there has been some recent work indicating possible differences in bioavailability and function on the part of K2; current knowledge is still very limited, and there is not enough evidence to displace K1 as the main formulation approved for dietary supplements [1,2].
I could go on and on with other inaccuracies in what you said, but you get the idea.
Also be careful with overdoing that liver with onions habit. Even though animal river is very rich in iron and copper (which likely explains part of how you feel after eating it); it also happens to contain high amounts of vitamin A in retinoid (retinol) form, which as you correctly point out should be taken in moderation due to their much higher bioavailability vis a vis carotenoids, thus increasing its potential toxicity [7].
[1] http://en.wikipedia.org/wiki/Iron_supplement
[2] http://www.webmd.com/vitamins-and-supplements/lifestyle-guid...
[3] http://www.medscape.com/viewarticle/589256_4
[4] http://www.ilsi.org/Europe/Documents/Menaquinones%20and%20hu...
[5] http://www.efsa.europa.eu/en/scdocs/doc/nda_op_ej822_vit_k2_...
[6] http://en.wikipedia.org/wiki/Liver_(food)
[7] http://en.wikipedia.org/wiki/Vitamin_A#Equivalencies_of_reti...