It's basically junk science (or a de-facto scam) by a guy who is doing well at marketing himself.
Food replacements already exist. The biggest is a product called Ensure. There are others. It's not clear that there's a need for Soylent at all.
You're right, iron deficiency can't be detected in a few days (3 months would be closer to the time frame required assuming you had healthy iron levels to begin).
Most of the other continual reformulations he discusses also seem pretty ridiculous on the timeframes involved. Basically, this guy doesn't seem to have any understanding of stochastic experimentation, limiting confounding factors or limiting free variables.
http://robrhinehart.com/?page_id=184
Adding ingredients, perceiving a difference in how he feels and then modifying the formula, claiming that he has "improved" based on testing.
He's not controlling for multiple changing variables, not sampling over a decent time period, not comparing to a control, not measuring his blood, vitals or other basic properties. He might as well be throwing things together randomly.
Using measurements and scientific terms without the rigour and actual method of scientific experimentation is junk science, by definition.
I thought he was getting weekly blood tests?
http://www.naturalnews.com/002698.html
It doesn't seem to me that any product made with high fructose corn syrup as its main ingredient represents a credible attempt to make a healthy food product (just using sugar would be healthier).
From Wikipedia (http://en.wikipedia.org/wiki/High-fructose_corn_syrup_and_he...):
> Epidemiological research has suggested that the increase in obesity is linked to increased consumption of sugars and/or calories in general, and not due to any special effect of fructose alone.[1]
If you're worried about "not natural" then meal replacements are not for you (unless you've had your stomach or jaws surgically removed). They are heavily processed and artificial by design.
It took me a long time to figure this out too, but when it hit me it was blindingly obvious in hind-sight.
Soylent is idiot-proof food.
Can't choose? Can't cook? Can't clean? Can't balance a meal to save your life? As it stands these people coast by on kraft dinner and ramen, and suffer for it.
Soylent is a convenient, relatively cheap ($7.50/person/day), relatively healthy default option. You can eat it without thinking and bad things won't happen. Heck, you don't even need a kitchen.
Whether or not the current incarnation lives up to these ideals has yet to be demonstrated, but that's why the idea appeals to so many people.
[citation needed]
(And it reminds me too much of baby formula, which is proven to be less healthy than the real stuff)...