A lot of people are excited about a deeply misguided project called Soylent, which inaccurately describes itself as "a drink that has enough of every essential nutrient the human body needs."
It is a drink. That part is accurate.
However, the exact number of nutrients a human body needs is unknown, and may be several orders of magnitude greater than Soylent's design assumes. For instance, a single tomato contains more than 70,000 phytochemicals, which are unique chemicals found only in plants (and often, unique chemicals found only in particular species and varieties of plants). Although consuming tomatoes often is very strongly correlated with a decreased incidence in cancers, it is unknown if any one specific phytochemical plays a decisive role in that effect, or if the effect only occurs when all 70,000+ phytochemicals operate in synergy together.
Or maybe it's just some subset of those 70,000+ phytochemicals, and that subset operates in synergy. Imagine trying to determine which phytochemicals were in that set, and which were not. You would need to study approximately 4.9 billion different combinations of those 70,000 phytochemicals, because 70,000 to the 2nd power is 4.9 billion. So you can fund 4.9 billion separate but related research efforts, after locating 4.9 billion separate groups of cancer patients, and developing 4.9 billion separate but related processes for extracting, isolating, and re-combining phytochemicals, or you could just remember to eat tomatoes, because they're good for you. Which move sounds more cost-effective?
(Update: OK actually, I'm not 100% sure what the number of necessary phytochemical research projects would be, but I do still think it's very safe to say it's a very large number.)
A similar story: Researchers found that daily servings of nuts were correlated with decreased incidence of heart attacks. So some other researchers tried to produce the same effects, but using only a subset of the total range of chemicals found in those nuts (specifically, the fatty acids). They failed.
Soylent is based on an absurdly oversimplified view of human health which fails to differentiate between nutrition and nutrients. It is very naïve in my opinion. I consider it the Bash on Balls of health, except Bash on Balls knows it's a joke.
Why you should consider my opinion: I lost 60 pounds in six months using superior nutrition. This lifestyle change also eliminated several very dangerous heart disease symptoms, as well as trivial allergy symptoms, tooth decay symptoms, and skin problems. It also lowered my blood pressure and cholesterol by a staggering degree in a very short space of time.
I would be very surprised if anybody experienced similar effects with a diet consisting entirely of Soylent.