This is quite ridiculous. We've mapped the nutrients required by our cells down to a molecular level. We've even got a thorough understanding of the interaction between the food we eat and how the microbial ecosystem in our digestive system breaks down our food as we digest it.
We have less understanding of the "natural" foods we eat. We've only mapped only a few genomes of the stable foods, let alone a complex break down of the exotic foods in the grocery store isle. The cocktail of organic molecules in the average fruit or vegetable is overwhelming, and many of them have been proved to be highly carcinogenic. Apples for example contain arsenic, amongst other poisonous chemicals. You get diarrhoea after eating too many fruits because of this. You also have pesticides, fertilisers, preservatives, and packaging contamination in 'natural' food.
I'm not against eating healthy, but the "we don't know if it causes cancer" banter is quite arrogant.
The concept of Soylent is great as it can be tailored for human requirements.